# Patent

## Title
Breath analysis system, device and method employing nanoparticle-based sensor

## Abstract

According to one aspect of the invention, the apparatus comprises a fluid collecting device configured to receive a sample of breath; a conditioning device coupled to the fluid collecting device and configured to receive the sample of breath and condition the sample with respect to at least one of temperature, flow rate, pressure, humidity, and concentration; and a sensing device coupled to the conditioning device and configured to receive the conditioned sample, wherein the sensing device includes a nanoparticle-based sensor and further whereby the analyte interacts with the sensing device to cause a change that is sensed by the sensing device and wherein the change comprises information useful in characterizing the analyte. Preferably, the apparatus is hand-held and characterizing the analyte is useful for health monitoring.

## Background
This application claims the priority benefit of U.S. Provisional Application No. 61/315,884, filed Mar. 19, 2010. The entire contents of this application is hereby incorporated by reference and for which priority is claimed under 35 U.S.C. §120.


BACKGROUND
Field
The invention relates generally to apparatus and methods for sensing analytes in a fluid, such as a liquid or a gas. A preferred example involves the sensing of one or more analytes in air or a gas expired by an individual for monitoring biochemical processes such as in diabetes, epilepsy, ovulation, weight loss, cholesterol biosynthesis, protein metabolism, and others occurring within that individual.
Background
There are many instances in which it is desirable to sense the presence and/or quantity of an analyte in a gas. “Analyte” as the term is used herein is used broadly to mean the chemical component or constituent that is sought to be sensed using devices and methods according to various aspects of the invention. An analyte may be or comprise an element, compound or other molecule, an ion or molecular fragment, or other substance that may be contained within a fluid. In some instances, embodiments and methods, there may be more than one analyte. “Fluid” as the term is used herein is used broadly to comprise a substance that is capable of flowing and that changes its shape when acted upon by a force. It includes liquids and gases, not only in their pure forms but also when in heterogeneous states, such as with slurries, suspensions, colloidal dispersions, and the like. Newtonian fluids are best suited to application in the present invention, but some degree of non-Newtonian behavior could be acceptable, depending on the specific application, and this is not intended to be limiting. “Gas” as the term is used herein also is used broadly and according to its common meaning to include not only pure gas phases but also vapors, non-liquid fluid phases, gaseous colloidal suspensions, solid phase particulate matter or liquid phase droplets entrained or suspended in gases or vapors, and the like. “Sense” and “sensing” as the terms are used herein are used broadly to mean detecting the presence of one or more analytes, or to measure the amount or concentration of the one or more analytes.
In many of these instances, there is a need or it is desirable to make the analysis for an analyte in the field, or otherwise to make such assessment without a requirement for expensive and cumbersome support equipment such as would be available in a hospital, laboratory or test facility. It is often desirable to do so in some cases with a largely self-contained device, preferably portable, and often preferably easy to use. It also is necessary or desirable in some instances to have the capability to sense the analyte in the fluid stream in real time or near real time. In addition, and as a general matter, it is highly desirable to accomplish such sensing accurately and reliably.
An example of the need for such devices is in the area of breath analysis. In the medical community, for example, there is a need for effective breath analysis to sense such analytes as acetone, isoprene, ammonia, alkanes, alcohol, and others, preferably using a hand-held or portable device that is relatively self contained, reliable and easy to use.
Historically, breath chemistry has not been very well exploited. Instead, blood and urine analysis has been performed. Blood analysis is painful, laborious, relatively expensive and often impractical due to lack of equipment or trained personnel. Typically blood analysis has been performed in a wet chemistry or hospital laboratory. Recently, there are two products that measure β-HBA levels that are made by GDS Diagnostics and Abbott Laboratories. While these companies have made home-testing possible, blood tests are still expensive and painful and they require careful disposal and procurement of employed equipment such as needles and collection vessels. This leads to low patient compliance.
Urine analysis has been criticized as being inaccurate. Urine analysis also is not time-sensitive in that the urine is collected in the bladder over a period of time.
Thus, while blood and urine tests can provide information about the physiological state of an individual, they have been relatively unattractive or ineffective for practical application where portability or field or home use is required.
Current systems used to sense an analyte in a gas, such as gas chromatographs and spectroscopy-related devices, are expensive, cumbersome to use, they require skilled operators or technicians, and otherwise typically are not practical for field or home use. They also tend to be quite expensive. Precision in detection systems usually comes at substantial cost. Current highly-accurate detection systems require expensive components such as a crystal, specialized power source, or containment chambers that are highly pH or humidity regulated.
Some systems for measuring analytes in air operate on electrochemical principles (see, e.g., U.S. Pat. No. 5,571,395, issued Nov. 5, 1996, to Park et al.), and some operate by infrared detection (see, e.g., U.S. Pat. No. 4,391,777 issued Jul. 5, 1983, to Hutson). U.S. Pat. No. 6,658,915, issued Dec. 9, 2003, to Sunshine et al., describes using chemically sensitive resistors to detect airborne substances and requires the use of an electrical source. U.S. Pat. No. 4,935,345, issued Jun. 19, 1990 to Guilbeau et al., describes the use of a single thermopile in liquid phase chemical analysis. However, the thermopile sensor is limited to measuring a single analyte and only a single reactant is present on the thermopile. This sensor operates in the liquid phase. Each of the foregoing patents is hereby incorporated herein by reference as if fully set forth herein.
SUMMARY OF THE INVENTION
According to one aspect of the invention, the apparatus comprises a fluid collecting device configured to receive a sample of breath; a conditioning device coupled to the fluid collecting device and configured to receive the sample of breath and condition the sample with respect to at least one of temperature, flow rate, pressure, humidity, and concentration; and a sensing device coupled to the conditioning device and configured to receive the conditioned sample, wherein the sensing device includes a nanoparticle-based sensor and further whereby the analyte interacts with the sensing device to cause a change that is sensed by the sensing device and wherein the change comprises information useful in characterizing the analyte. Preferably, the apparatus is hand-held and characterizing the analyte is useful for health monitoring.
According to another aspect of the invention, a method is provided for sensing an analyte in breath. The method comprises providing a fluid collecting device for receiving a sample of breath, providing a conditioning device coupled to the fluid collecting device, receiving the sample of breath in the conditioning device, conditioning the sample with respect to at least one of temperature, flow rate, pressure, humidity, and concentration, providing a sensing device that is coupled to the conditioning device and which is configured to receive the conditioned sample, wherein the sensing device further comprises a nanoparticle-based sensor, causing the analyte to interact with the sensing device to cause a change, and sensing the change by the sensing device wherein the change comprises information useful in characterizing the analyte.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate a presently preferred embodiments and methods of the invention and, together with the general description given above and the detailed description of the preferred embodiments and methods given below, serve to explain the principles of the invention. Of the drawings:
FIG. 1 shows is a composite illustration of sensor details and a device in use;
FIG. 2 is a schematic top view of a rectangular thermopile suitable for use in FIG. 1;
FIG. 3 is a schematic showing a circular thermopile;
FIG. 4 shows a side cross-section of a thermopile sensor as it was installed in a housing;
FIG. 5 illustrates the top view of the sensor illustrated in FIG. 4;
FIG. 6 shows the results of a test of the sensor illustrated in FIGS. 4 and 5 for four analyte concentrations;
FIG. 7 summarizes sample test results by showing the peak sensor output voltage as a function of analyte concentration;
FIG. 8 shows theoretical curves for the same sensor and analyte concentrations as show in FIG. 6;
FIG. 9 shows the sensor response to analyte that was transferred only by diffusion;
FIG. 10 shows a possible embodiment for use in a hospital environment using a patient gas mask;
FIG. 11 shows a first possible chemical immobilization technique for chemical amplification;
FIG. 12 shows a second possible chemical immobilization technique for chemical amplification;
FIG. 13 depicts a side view of the technique shown in FIG. 11 and FIG. 12;
FIG. 14 shows the top view of a possible embodiment of an optimized chemical sensor;
FIG. 15 depicts the side view of a possible embodiment of an optimized chemical sensor;
FIG. 16 shows a embodiment of a gas sensor using a condenser;
FIG. 17 depicts a method for creating a thermopile in a catheter style;
FIG. 18 shows a method for immobilizing chemical on the sensor described by FIG. 17;
FIG. 19 shows an embodiment of a thermopile;
FIG. 20 shows a embodiment of a thermopile;
FIG. 21 shows a layout of a device using multiple thermopiles;
FIG. 22 shows a layout of a device using multiple thermopiles;
FIG. 23 shows a flow chamber;
FIG. 24 shows another embodiment of a flow chamber;
FIG. 25 shows a three dimensional construction of sensor housing;
FIG. 26 is a flow diagram illustrating a preferred embodiment and its operation;
FIG. 27 shows placement of the thermopile within the sensor housing;
FIG. 28 shows a user blowing into a sensor according to a preferred embodiment of the invention that utilizes filters;
FIG. 29 is a graph showing the cumulative flux of analyte as a function of distance from the leading edge of a surface;
FIG. 30 is a graph illustrating a method for selecting conduit height;
FIG. 31 is another graph illustrating a method for selecting conduit height;
FIG. 32 is another graph illustrating a method for selecting conduit height;
FIG. 33 is a functional block diagram illustrating the configuration of an embodiment of one aspect of the invention;
FIG. 34 is another functional block diagram illustrating the configuration of an embodiment of one aspect of the invention;
FIG. 35 is an embodiment of the invention that utilizes a temperature compensating unit;
FIG. 36 is a perspective diagram of an embodiment of the invention;
FIG. 37 is an embodiment of the invention that utilizes one or more sensors;
FIG. 38 is an embodiment of a pyroelectric sensor with immobilized analyte interactant;
FIG. 39 is an embodiment of a thermal sensor with analyte interactant contained within a packed bed;
FIG. 40 is an embodiment of a thermal sensor that measures radiated heat from an enthalpic interaction;
FIG. 41 is an embodiment that utilizes control valves to provide modulation;
FIG. 42 is an embodiment that utilizes a charged surface;
FIG. 43 is an embodiment that utilizes magnetic surfaces;
FIG. 44 is an embodiment that utilizes a heater;
FIG. 45 is an embodiment that utilizes a test strip;
FIG. 46 is an embodiment that utilizes a test strip with a control valve and mixer;
FIG. 47 is an embodiment that utilizes a circular test strip;
FIG. 48 is an embodiment that utilizes a mechanical chopper;
FIG. 49 is an embodiment that utilizes a mechanical chopper to detect thermal energy from a packed bed;
FIG. 50 is an embodiment that utilizes mass discrimination principles;
FIG. 51 is an embodiment with two sensors for enhanced specificity;
FIG. 52 is an embodiment with multiple binding sites;
FIG. 53 is an embodiment that utilizes a concentrator; and
FIG. 54 is an embodiment of a pyroelectric sensor.
FIG. 55 is a functional block diagram illustrating the configuration of an embodiment of one aspect of the invention;
FIG. 56 is an embodiment that utilizes two conditioning devices and a sensing device.
FIG. 57 is an embodiment of a hand-held breath gas analyzer with a nanoparticle-based sensing device.
FIG. 58 is a compilation of four embodiments of conditioning devices.
FIG. 59 is a top view of an embodiment of a nanoparticle-based sensor.
FIG. 60 is a bottom view of an embodiment of a nanoparticle-based sensor.
FIG. 61 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone.
FIG. 62 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone.
FIG. 63 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone.
FIG. 64 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone.
FIG. 65 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone.
FIG. 66 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to oxygen.
FIG. 67 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to isopropanol.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS AND METHODS
Reference will now be made in detail to the presently preferred embodiments and methods of the invention as illustrated in the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the drawings. It should be noted, however, that the invention in its broader aspects is not limited to the specific details, representative devices and methods, and illustrative examples shown and described in this section in connection with the preferred embodiments and methods. The invention according to its various aspects is particularly pointed out and distinctly claimed in the attached claims read in view of this specification, and appropriate equivalents.
In accordance with one aspect of the invention, an apparatus is provided for sensing an analyte in a fluid. To illustrate this aspect of the invention, an analyte-in-gas sensor 2 according to a presently preferred embodiment of this aspect of the invention is shown in FIG. 1 in conjunction with a patient or other user 1. Although this sensor apparatus could be used in a variety of applications, in this illustrative example it is adapted for use as an acetone sensor for sensing gas or vapor phase acetone in the breath of a human patient or user. Before describing this embodiment in detail, some background on this acetone-sensing application would be useful in appreciating the usefulness of the device and related methods.
Approximately 300 analytes have been identified in human breath. Examples include but are not limited to pentane and other alkanes, isoprene, benzene, acetone and other ketones, alcohols such as ethanol, methanol, isopropanol, ammonia, reflux, medication, and substances which interfere with common alcohol detection systems such as acetaldehyde, acetonitrile, methylene chloride, methyl ethyl ketone, and toluene. Some analytes are in vapor form while others may be in particle form.
Ketone bodies provide a supplementary or substitute form of energy that can be used during various metabolic states including stress, starvation, caloric regulation, or pathology. Breath acetone levels, for example, often are elevated during various metabolic states including stress, starvation, caloric regulation, or pathology such as diabetes and epilepsy. Oftentimes in diabetics, for example, low insulin levels and elevated blood glucose levels result in high concentrations of ketones in the body. This could potentially cause diabetic ketoacidosis (“DKA”).
Patients in DKA commonly experience many symptoms such as nausea, fatigue, and rapid breathing. They also emit a fruity odor in their breath, which is distinct and attributable to acetone. Acetone is a volatile ketone body released into alveolar air. If left untreated, DKA can result in coma or even death. However, DKA often is preventable if ketone levels are monitored and treatment is sought when ketone counts are high. The current methods of ketone measurement are blood and urine analysis. The current blood tests typically are accurate, but their invasive nature is undesirable and frequently causes patients to delay treatment. Blood tests also are expensive, as a number of products are employed, including a lancet for blood letting, test strips, a specialized device and batteries. Several studies show that urine analysis is not accurate.
Ketone monitoring also is becoming recognized as a tool for nutritionists or health care professionals to monitor lipid metabolism during dieting. Several studies show that breath acetone concentrations represent lipid metabolism during a calorie deficit. Obesity has become increasingly prevalent and has now reached epidemic levels. It is consequently of great concern to healthcare professionals. Much effort has been invested in treating obesity and promoting healthy weight loss programs for obese individuals. For treatment of obesity, a sensor that measures fat burning would permit patients, doctors and nutrition advisors to adjust weight management plans to individual physiology. A noninvasive, inexpensive, simple-to-use acetone sensor would be an appropriate tool for nutritionists, physicians, and the general public who seek to monitor fat metabolism.
In view of this, sensor 2, while merely illustrating preferred embodiments and method implementations of various aspects of the invention, is specifically adapted to analyze the breath of a patient or other user 1 to sense the specific analyte acetone in the gas phase that constitutes the user's breath as it is expired into the sensor 2. Moreover, this sensor 2 provides the ability to sense acetone levels in the breath of an individual with relatively high accuracy to aid in assessment and treatment in areas such as those described herein above.
Sensor 2 comprises a fluid collecting device for collecting the fluid containing the analyte. Sensor 2 further comprises a fluid input in fluid communication with the fluid collecting device for inputting the fluid containing the analyte in to the fluid collecting device. The fluid collecting device may be or comprise any apparatus that is configured to contain the analyte. Similarly, the fluid input may be or comprise any apparatus that is configured to input the fluid containing the analyte into the fluid collecting device. For example, the fluid collecting device may be or comprise one or more of the following: a conduit, a cavity, a sample collection bag (e.g., a Tedlar bag), etc. The fluid input device may be or comprise one or more of the following: a mouthpiece, a flow controller, a flow restrictor, a filter, a valve, a sterile piece, an injection port, an opening/orifice, a sampling pump, a face mask, a breathing tube, etc.
A fluid collecting device may be any apparatus whereby a sample of breath is captured or admitted. The fluid collecting device may include means for the user to deliver a breath sample. The fluid collecting device may also include means for the analyte to be delivered to the sensing device. The fluid collecting device may also include a means for detection that a sampling event has occurred. One example of this is a thermal sensor that registers an increase in the temperature of the air in the flow conduit in response to the user breathing into the fluid collecting device. A second example of this is a pressure sensor that registers an increase in the inlet pressure of the fluid collecting device in response to the user breathing into the fluid collecting device.
The fluid collecting device may be a user mouthpiece. A mouthpiece coupled to a nose-clip may be useful for certain applications where there is concern that the user will expire physiologically-relevant gas samples through his or her nose and mouth. The fluid collecting device may also be a facemask where the sample of breath is collected via the nasal passageway. The facemask may be particularly useful when a user is unconscious or otherwise experiencing difficulty with forced expiration, such as when a patient has sustained an injury to his or her diaphragm or lungs.
The fluid collecting device may be configured to receive the sample of breath from the user directly or from a breath storage unit. For example, the fluid collecting device may accept breath sample from a Tedlar bag.
As specifically embodied in sensor 2, the fluid collecting device comprises a gas collecting device comprising a conduit 4. Other fluid or gas collecting device designs, however, are possible and may be used, provided that the fluid collecting device physically contains or directs the flow or position of the fluid so that it can undergo the desired reaction or interactions as described more fully herein below.
Modified or alternative fluid or gas input devices also may be used. Mouthpiece 3, for example, may be equipped with such modifications as a one-way valve, a pressure regulator, a flow rate regulator, a dessicant or dehumidifier, and the like.
A sample of breath may be a volume of breath from a single or a plurality of exhalations, which may be from either the mouth, nose, or some combination thereof. The sample of breath may be delivered directly to the apparatus for sensing analytes in breath or it may be delivered to a breath storage unit, such as a Tedlar bag or a stainless steel vessel for later analysis. The sample of breath is delivered to the apparatus for sensing analytes in breath as a single bolus for a given analysis.
Traditionally and commonly, chemical sensors operate in an environment with continuous fluid flow. When there is continuous fluid flow, experiments are typically performed using flow-injection analysis. In this method of analysis, the sensor reaches equilibrium with fluid flow and then the analyte is “injected” into the fluid stream. In this way, the only variable that changes is the presence of the analyte.
Sensing analytes in boluses of a fluid can be a complex task. Being able to sense analytes when there is a finite volume of a fluid requires that the sensing device sense the analyte despite substantial changes in the background. In other words, the presence of the analyte is not necessarily the only variable that is changing, and the sensing devices may exhibit sensitivity to changes in these other variables which obscure the changes caused to the sensing device by the analyte of interest.
Commercialization of breath sensing systems poses substantial challenges. The background matrix of breath presents numerous challenges to sensing systems, which necessitate complex processing steps and which further preclude system integration into a form factor suitable for portable usage by layman end-users. For example, breath contains high levels of humidity and moisture, which may interfere with the sensor or cause condensation within the hand-held device, amongst other concerns. Also, the flow rate or pressure of breath as it is collected from a user typically varies quite considerably. Flow rate variations are known to impact, often significantly, the response of chemical sensors. Breath, especially when directly collected from a user, is typically at body temperature, which may be considerably different than the ambient temperature. Additionally, body temperature may vary from user to user or from day to day, even for a single user. Devising a breath analyzer thus is not trivial.
As explained above, development of a breath analyzer is a complex task. However, the challenges do not end there. Developing a breath analyzer conducive to a hand-held embodiment is even more complex. This makes perfect sense given that research into breath analysis has been very active since the 1950s and yet, to date, commercially available hand-held breath analyzers for health monitoring are not available. Given the enormous potential behind noninvasive health monitoring, it stands to reason that addressing the challenges associated with sensing analytes in breath and doing so in a hand-held device is significant.
A hand-held breath gas analyzer that can be used by a layman presents new opportunities for both improved healthcare and also advances in fundamental science. Hand-held breath sensing systems create comfortable and more natural sampling to increase user adherence to a desired sampling schedule. Furthermore, at least one embodiment disclosed herein decouples sampling from analysis, which also potentially increases user adherence to a desired sampling schedule: a user blows into the system and the system captures the breath sample. The manner in which the breath sample is collected is independent of sample analysis. This is useful in that many breath analysis devices require the user to blow through uncomfortable collection devices for rather lengthy times. Since sampling apparatus and procedures can be designed independent of sample analysis, the system presented herein potentially allows a user to breathe into a breath collection subsystem in a manner that is more comfortable in terms of the force or pressure required for sample introduction into the device as well as in terms of the time required of the user to deliver a sufficient amount of breath to be analyzed in a repeatable and clinically relevant fashion.
Herein, apparatuses are presented for sensing an analyte in breath in various configurations including hand-held embodiments for sensing multiple analytes in human breath for management of health and disease.
A range of analytes can be sensed using embodiments and method implementations of the invention according to its various aspects. In addition, embodiments and methods can be used to sense one analyte or more than one. Examples of analytes and applications that are amenable to these aspects of the invention include but are not limited to the following primary market groups:
(a) Medical devices/nutritional monitors—breath analysis;
(b) Chemical toxicity and/or occupational health and safety compliance—breath analysis for employees who work in an environment where they are inhaling chemicals—e.g., to assess such things as how much are they exhaling, how much is being internalized, whether they are within acceptable limits, etc.;

(c) Law enforcement—e.g., drug or alcohol testing (G-HBA, cannabis, ethanol, etc.); and

(d) Environmental monitoring.

One area of particular interest involves breath analysis. Included among illustrative breath constituents, i.e., analytes, that have been correlated with disease states are those set forth in Table 1, below. As noted, there are perhaps 300 volatile organic compounds that have been identified in the breath, all of which are candidate analytes for analysis using such embodiments and methods. Additionally, in some instances combinations of constituents (analytes) in breath may serve as a superior disease marker relative to the presence of any single analyte.









TABLE 1






CANDIDATE
ILLUSTRATIVE


No.
ANALYTE
PATHOPHYSIOLOGY/PHYSICAL STATE

















1.
Acetone
Lipid metabolism (e.g., epilepsy




management, nutritional monitoring, weight




loss therapy, early warning of diabetic




ketoacidosis), environmental monitoring,




acetone toxicity, congestive heart failure,




malnutrition, exercise, ovulation


2.
Ethanol
Alcohol toxicity, bacterial growth


3.
Acetaldehyde



4.
Ammonia
Liver or renal failure, protein metabolism


5.
Isoprene
Lung injury, cholesterol synthesis, smoking




damage


6.
Pentane
Lipid peroxidation (breast cancer, transplant




rejection), oxidative tissue damage, asthma,




smoking damage, COPD


7.
Ethane
Smoking damage, lipid peroxidation, asthma,




COPD


8.
Alkanes
Lung disease, cancer metabolic markers


9.
Benzene
Cancer metabolic monitors


10.
Carbon-13
H. pylori infection


11.
Methanol
Ingestion, bacterial flora


12.
Leukotrienes
Present in breath condensate, cancer markers


13.
Hydrogen peroxide
Present in breath condensate


14.
Isoprostane
Present in breath condensate, cancer markers


15.
Peroxynitrite
Present in breath condensate


16.
Cytokines
Present in breath condensate


17.
Glycans
Glucose measurement, metabolic anomalies




(e.g., collected from cellular debris)


18.
Carbon monoxide
Inflammation in airway (asthma,




bronchiesctasis), lung disease


19.
Chloroform



20.
Dichlorobenzene
Compromised pulmonary function


21.
Trimethyl amine
Uremia


22.
Dimethyl amine
Uremia


23.
Diethyl amine
Intestinal bacteria


24.
Methanethiol
Intestinal bacteria


25.
Methylethylketone
Lipid metabolism


26.
O-toluidine
Cancer marker


27.
Pentane sulfides
Lipid peroxidation


28.
Hydrogen sulfide
Dental disease, ovulation


29.
Sulfated 
Cirrhosis



hydrocarbon



30.
Cannabis
Drug concentration


31.
G-HBA
Drug testing


32.
Nitric oxide
Inflammation, lung disease


33.
Propane
Protein oxidation, lung disease


34.
Butane
Protein oxidation, lung disease


35.
Other Ketones (other 
Lipid metabolism



than acetone)



36.
Ethyl mercaptane
Cirrhosis


37.
Dimethyl sulfide
Cirrhosis


38.
Dimethyl disulfide
Cirrhosis


39.
Carbon disulfide
Schizophrenia


40.
3-heptanone
Propionic acidaemia


41.
7-methyl tridecane
Lung cancer


42.
Nonane
Breast cancer


43.
5-methyl tridecane
Breast cancer


44.
3-methyl undecane
Breast cancer


45.
6-methyl
Breast cancer



pentadecane



46.
3-methyl propanone
Breast cancer


47.
3-methyl
Breast cancer



nonadecane



48.
4-methyl dodecane
Breast cancer


49.
2-methyl octane
Breast cancer


50.
Trichloroethane



51.
2-butanone



52.
Ethyl benzene



53.
Xylene (M, P, O)



54.
Styrene



55.
Tetrachloroethene



56.
Toluene



57.
Ethylene



58.
Hydrogen



59.
Oxygen
Basal metabolic rate, oxygen consumption,




fat metabolism


60.
Carbon dioxide
Basal metabolic rate, fat metabolism


61.
Isopropanol
Fat metabolism, acetone conversion, lipid




metabolism (e.g., epilepsy management,




nutritional monitoring, weight loss




therapy, early warning of diabetic




ketoacidosis)









Examples of other analytes would include bromobenzene, bromochloromethane, bromodichloromethane, bromoform, bromomethane, 2-butanone, n-butylbenzene, sec-butylbenzene, tert-butylbenzene, carbon disulfide, carbon tetrachloride, chlorobenzene, chloroethane, chloroform, chloromethane, 2-chlorotoluene, 4-chlorotoluene, dibromochloromethane, 1,2-dibromo-3-chloropropane, 1,2-dibromoethane, dibromomethane, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, dichlorodifluoromethane, 1,1-dichloroethane, 1,2-dichloroethane, 1,1-dichloroethene, cis-1,2-dichloroethene, trans-1,2-dichloroethene, 1,2-dichloropropane, 1,3-dichloropropane, 2,2-dichloropropane, 1,1-dichloropropene, cis-1,3-dichloropropene, trans-1,3-dichloropropene, ethylbenzene, hexachlorobutadiene, 2-hexanone, isopropylbenzene, p-isopropyltoluene, methylene chloride, 4-methyl-2-pentanone, methyl-tert-butyl ether, naphthalene, n-propylbenzene, styrene, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, tetrachloroethene, toluene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethene, trichlorofluoromethane, 1,2,3-trichloropropane, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, vinyl acetate, vinyl chloride, xylenes, dibromofluoromethane, toluene-d8,4-bromofluorobenzene.
Embodiments and methods according to these aspects of the invention may be employed to measure disease markers in the breath, where either elevated or low levels may be important for diagnostic purposes. As noted above, for example, diabetic ketoacidosis (DKA) is a condition where ketone levels in the body are abnormally high. Hyperosmolar non-ketotic syndrome is a condition where ketone levels in the body are subnormal, meaning that the body is not producing enough ketone bodies for normal functioning. While in some embodiments, the sensor may be employed to measure changes in analyte concentrations in a fluid, it is not limited to this and can measure absolute concentrations instead or as well.
A hand-held breath acetone analyzer can be used to monitor ovulation. During ovulation, the body temperature increases and accordingly metabolic activity increases, which results in an increase in blood ketones and thereby breath acetone. Current ovulation tests involve either urine or blood analysis. A breath test, particularly a hand-held breath test, provides a compelling way for individuals to conveniently and simply monitor ovulation. Such a device may also monitor body temperature and be configured to track or log values over time so that the user may make informed decisions about family planning.
The analyte may be acetone and a second analyte and the concentration of both acetone and this second analyte may be useful in monitoring a health condition.
For example, acetone and oxygen and/or carbon dioxide may be used to monitor fat metabolism. Monitoring oxygen or carbon dioxide can provide information about an individual's basal metabolic rate. The basal metabolic rate varies, especially when an individual has made changes in his or her diet or exercise program. A combined acetone and oxygen device, therefore, may provide a physician or user with increased information and enable more informed nutritional and weight loss intervention programs.
Under certain physiological circumstances, acetone and isopropanol are in a state of chemical equilibrium. If acetone levels increase, the reverse reaction may occur and acetone may be converted into isopropanol. This has been observed with alcohol breath analyzers used for “during the influence” DUI purposes. Even if the DUI breathalyzer is not sensitive to acetone, if a user is in a state with elevated ketone levels, such as diabetic ketoacidosis, acetone may be converted into isopropanol, which is an alcohol, and therefore detectable by the breathalyzer. Thus, elevated levels of breath acetone may result in a false positive by a DUI breathalyzer because acetone may be converted into isopropanol and the latter analyte can be detected by the DUI breathalyzer. However, when acetone converts to isopropanol, a second problem can exist. If acetone is converted to isopropanol, a breath acetone sensor may under-determine the levels of breath acetone. For these situations, the sum total of breath isopropanol levels and breath acetone levels may actually serve as a better indicator of ketone levels than breath acetone alone. Accordingly, a dual-analyte embodiment that senses acetone and isopropanol has tremendous advantages, particularly in critical care situations where acetone levels are extremely high and where acetone may be converted to isopropanol.
In other cases, measuring acetone in connection with other analytes, such as ammonia, isoprene, and markers of oxidative stress would enable superior health monitoring. In the case of diabetes, for instance, monitoring breath acetone, ammonia, and isoprene may serve as a rapid means to determine blood ketone, creatinine or BUN, and cholesterol levels.
A hand-held breath analyzer that senses multiple analytes may be useful to monitor seemingly unrelated disease states, for example diabetes and asthma. Such a device may utilize disposable cartridges that are application-specific. A single family may purchase a single hand-held device and utilize this device with application-specific cartridges. In this way, one individual may monitor his or her asthma and another individual may use the same device to monitor his or her diabetes.
Sensor 2 further comprises an analyte interactant 6 (or “interactant 6”) that, when contacted by the analyte of interest—here acetone—reacts to cause a change in thermal energy within the fluid collecting device. The analyte may be any substance that is capable of reacting with the analyte to cause the desired change in thermal energy. Although the list of candidate analyte interactants provided here is not necessarily exhaustive, presently preferred analyte interactants would include those described herein, and others as well. “React” as the term is used herein includes not only chemical reaction, but other forms of reaction in which the state of the analyte and/or analyte interactant, their properties or state, or the properties or state of their environment is changed. Examples of reaction regimes might include, for example, physical or chemical absorption or adsorption, physical or chemical reaction, Van der Waals interactions, transitions that absorb or release thermal energy, and the like.
The analyte interactant is in fluid communication with the fluid collecting device in the sense that the analyte interactant is positioned relative to the gas collecting device so that the gas received into the gas collecting device contacts the analyte interactant so that the desired or anticipated analyte-analyte interactant reaction can occur. Preferably, and particularly where the fluid collecting device comprises a cavity or conduit, the analyte interactant is positioned within the cavity or conduit so that at least a portion of the fluid entering the cavity or conduit is caused or permitted to contact and react with the analyte interactant. Alternative designs, however, are possible. An example would comprise placing the analyte interactant at an exit orifice of the fluid collecting device or outside of but immediately adjacent to a portion of the fluid collecting device.
The change in thermal energy associated with the analyte and analyte interactant reaction may involve an increase or a decrease. This thermal energy change may and preferably does have associated with it a change in associated temperature of materials associated with or constituting the sensor 2, but may be used directly, for example, by utilizing a thermal energy flow isothermally.
The analyte interactant 6 preferably is disposed on a substrate such as substrate 7 in FIG. 1 to physically support the interactant and to receive at least a portion of the thermal energy liberated by the analyte-analyte interactant reaction, or to provide thermal energy where the reaction consumes thermal energy.
Sensor 2 also comprises a thermal sensor 5 that in this illustrative embodiment comprises at least one thermocouple, thermopile device, or pyroelectric device thermally coupled to the gas collecting device to generate a signal in response to the change in thermal energy. The signal comprises information useful in characterizing the analyte. The thermal sensing device is thermally coupled to the gas collecting device in the sense that the thermal sensing device, or at least a portion of the thermal sensing device that is used for sensing thermal energy, is disposed so that it can sense at least a portion of the thermal energy generated by the analyte-analyte interactant reaction. The thermopile device therefore need not necessarily be located within the gas collecting device, although preferably it will be located within the gas collecting device or contiguous with it, e.g., such as by forming a wall or panel of the gas collecting device.
“Thermocouple” as the term is used herein is used in its common or ordinary meaning in the fields of physics and engineering and comprises a temperature or thermal energy sensing or measuring device in which a first material is joined or contacted with a second material different from the first material so that an electromotive force is induced by thermoelectric effect when the first and second materials are at different temperatures. The term “thermoelectric thermometer” also is used to describe a thermocouple. The first and second materials used to construct the thermocouple usually are conductors such as metals, alloys, or liquid thermoelectric materials that may or may not contain dopants.
The thermocouple comprises a point of contacts that are called “thermoelectric junctions.” One of the junctions is referred to as a “reference junction” and the other is referred to as a “sensing junction.” A temperature gradient between the two thermoelectric junctions causes electrons to travel toward the colder region which causes a potential difference between the junctions. This is called the “thermoelectric effect.”
This potential difference or voltage between the two junctions is described as follows: V=n·S·ΔT where V is the voltage, n is the number of thermocouples, S is the Seebeck coefficient of the two metals, and ΔT is the temperature difference between the sensing and reference junctions. Amongst pure metals, antimony and bismuth have the highest Seebeck coefficient.
The thermal sensing device or thermal sensor as implemented in illustrative sensor 2 comprises a thermopile device 8.
A “thermopile” as the term is used herein is used in its common and ordinary meaning in the fields of physics and engineering to refer to a device that comprises a plurality of thermocouples connected in series. The voltage output of a thermopile is proportional to the Seebeck coefficient of the metals, the number of thermocouples, and the temperature difference between the sensing and reference junctions.
There is design flexibility in the physical relationship of the analyte interactant and the thermal sensor, provided that at least a portion, and preferably most, of the thermal energy from the analyte-analyte interactant reaction is communicated to the sensing portion of the thermal sensor 5. One approach is to place the analyte interactant on or immediately adjacent to the sensing portion of the thermal sensor. In sensor 2, for example, one preferably would coat the sensing junctions, and not the reference junctions, of the thermocouple or thermopile, with the analyte interactant.
An exploded cross sectional view of sensor 2 depicting details of the thermal sensor 5 is shown in the lower right portion of FIG. 1. That cross sectional view shows the analyte interactant 6 disposed on a substrate 7. Immediately below the substrate 7 lies the thermopile device 8, and immediately below it is a thermal insulating material.
FIG. 2 shows a schematic top or plan view of a rectangular thermopile device 8 suitable for use in the thermal sensor 5 shown in FIG. 1. The thermopile device 8 comprises two dissimilar conductors that are deposited on a substrate 13 as alternating strips of conductors 14. The conductors are patterned such that there are two sets of junctions between conductors, the sensing junctions 10 and the reference junctions 11. One of the conductors spans the distance between any reference and sensing junction, which are all in series electrically. As a result, the voltage between the contact pads 12 is the sum of the EMFs of the individual thermocouples which are each made up of a single sensing junction (from the sensing junction set 10) and a single reference junction (from the reference junction set 11). Normally thermopiles are arranged to have an equal number of each. As illustrated in FIG. 2, there are about 60 of each in this embodiment.
Sensor 2 optionally may and preferably will further comprise a processing device operatively coupled to the thermocouple device to receive the signal and process it. This processing device may comprise any device capable of performing the processing desired of the sensor 2, e.g., as described herein. Preferably, however, the processing device comprises a microprocessor or microcontroller, as will be described in greater detail herein below.
The voltage output of the thermopile device 8 can be measured directly or by use of this processing device. The processing device may report the voltage or may convert the voltage to a concentration or other interpretable signal. This conversion may be programmed by use of a calibration curve, look-up table, or other method.
Optionally, the processing device may be used to provide feedback, which feedback can be programmed to analyze the status and transmit commands to operate similar to a drug delivery device.
The thermopile voltage will vary as a function of the temperature difference across its sensing and reference junctions, which normally will change over the course of the analyte-analyte interactant enthalpic interaction. For instance, certain chemical reactions propagate and get increasingly more exothermic as they proceed. Additionally, depending on such things as the flow conditions, the output voltage may change. Therefore, it may be necessary for the processing device to process the signal to ascertain information about the reaction system and to translate the sensor-derived signal into useful information usable by the user. Examples of the types of signal characteristics or responses that have been found meaningful with devices and methods according to this aspect of the invention include the peak voltage, the slope of the voltage versus time curve, the area under the voltage versus time curve, the time to reach various signal features, and the steady state values, etc. Depending on the time over which the analyte interacts with the interactant, different signals may be more indicative of the analyte concentration.
Sensor 2 may also be or comprise a pyroelectric device that is adapted to sense thermal energy from an analyte-analyte interactant reaction in a fluid. Among thermal sensors, pyroelectric materials tend to exhibit fast response times. Additionally, the response of a pyroelectric material to a given energy input may be orders of magnitude greater than other thermal sensors. Embodiments and methods involving the pyroelectric sensor can be applied to fluids broadly, which includes not only gases but liquids as well.
Pyroelectric materials produce an electric current when heated or cooled. Pyroelectrics measure the rate of change of temperature as shown in the following equation:




  I
  =
  
    
      p
      ⁡
      
        (
        T
        )
      
    
    ·
    A
    ·
    
      
        d
        T
      
      
        d
        t
      
    
  




where I is current, A is surface area of the sensing element, p(T) is the pyroelectric coefficient, which is a function of temperature, and T is temperature.

Fundamentally, the crystal lattice of certain materials, including ferroelectrics, includes nonsymmetrical bound ions. These ions give rise to spontaneous electric polarization. As with other thermal detectors, the response of the pyroelectric sensor is generally improved if the detector thickness and volumetric heat capacity are minimized.
There are a number of pyroelectric materials that can be employed in various embodiments and methods according to this aspect of the invention. For instance, synthetic and natural (e.g., minerals and ionic crystals) materials may be used. Some examples of pyroelectric materials would include: triglycine sulfate, quartz, tourmaline, gallium nitride, polyvinyl fluorides (e.g. PVDF), lithium tantalate, lead zirconate titanate, lead titanate, etc. It should be understood that any other material or combination of materials that exhibit appropriate pyroelectricity may be a candidate for use.
It is advantageous to note the relationship between the pyroelectric relaxation frequency and the frequency of the heat input modulation. The response of the pyroelectric element typically is enhanced by high-frequency heat. Thus, it is usually helpful if the signal is pulsed or in some way modulated or chopped. This signal can be modulated by a number of different techniques and examples are provided hereinafter. However, as is discussed herein, this modulation is not always necessary.
This pyroelectric chemical sensor may be employed in a number of different applications and environments to measure a number of analytes. For example, a pyroelectric chemical sensor can be used to measure analytes in liquids or gases. Examples of liquids include blood, synovial fluid, spinal fluid, urine, water-based solutions, etc. The array of analytes is also extremely broad. Also, the analyte interactants that can be used with embodiments and methods that employ pyroelectric sensors are broad, as described herein (examples include absorbents, adsorbents, chemical reactants, hydrogenation reagents, aptamers, vapochromic materials, lectins, antibodies, etc).
Sensor 2 may also be or comprise a nanoparticle-based sensor. According to one aspect of the invention, the apparatus comprises a fluid collecting device configured to receive a sample of breath; a conditioning device coupled to the fluid collecting device and configured to receive the sample of breath and condition the sample with respect to at least one of temperature, flow rate, pressure, humidity, and concentration; and a sensing device coupled to the conditioning device and configured to receive the conditioned sample, wherein the sensing device includes a nanoparticle-based sensor and further whereby the analyte interacts with the sensing device to cause a change that is sensed by the sensing device and wherein the change comprises information useful in characterizing the analyte.
According to another aspect of the invention, a method is provided for sensing an analyte in breath. The method comprises providing a fluid collecting device for receiving a sample of breath, providing a conditioning device coupled to the fluid collecting device, receiving the sample of breath in the conditioning device, conditioning the sample with respect to at least one of temperature, flow rate, pressure, humidity, and concentration, providing a sensing device that is coupled to the conditioning device and which is configured to receive the conditioned sample, wherein the sensing device further comprises a nanoparticle-based sensor, causing the analyte to interact with the sensing device to cause a change, and sensing the change by the sensing device wherein the change comprises information useful in characterizing the analyte.
As may be appreciated from this description, the sensor may be used in a wide variety of implementations and methods. Moreover, the sensor may be used in conjunction with different components that may, for example, aid in the regulation, interpretation, and/or maintenance of the environment and conditions surrounding analysis. As such, the sensor or processing unit (e.g. microprocessor, microcontroller) may be required to process a substantial amount of information. As such, it may be desirable to test a variety of different signal interpretation methods to determine a reliable indicator of analyte concentration or presence.
The output of the thermal sensor, e.g., the voltage/current versus time curve, may be analyzed in a number of ways, including the peak-to-peak difference, maximum value, minimum value, slope of the curve, area under the curve, time to reach certain points, steady state values, etc. Different methods may be employed to determine these features. For example, the area under the curve may be computed using the Trapezoid Rule or the Midpoint Rule. Or, the slope may be computed using, for example, ten data points or one hundred data points, depending on the situation.
Additionally, combinations of such features and interactions of such features can be considered. For example, if the steady state value is above value=X, then the peak to peak difference ought to be interpreted according to method Y. Alternatively, if the area under the curve=X, this means that the flow rate=Y and if the flow rate=Y, then the peak-to-peak difference can be scaled by factor Z to more accurately predict the concentration of the analyte. These are mere examples; others of course may be implemented depending on the components, signal, circumstances, conditions of analysis, analyte-analyte interactant interaction, etc.
In addition to the output of the thermal sensor, other factors may also be considered. For example, the processor may consider the output of multiple thermal sensors which are coated with the same analyte interactant. In this instance, the processor may average the outputs or it may discard outliers prior to analysis. In other instances, the processor may consider the output of multiple thermal sensors each of which is coated with a different analyte interactant. This may affect the processing algorithm. For example, perhaps the processor interprets the output of thermal sensor #2 to mean that the concentration of analyte #2 is X; the processor may then interpret the output of thermal sensor #5 accounting for fact that the concentration of analyte #2 is X.
In analyzing the signal, the processor may account for the output of components other than the thermal sensor. For example, the processor may be coupled to a flow measuring device, an ambient temperature gage, a filtering unit, or a combination of components. In such instances, the algorithm for signal interpretation may be more complex and involve multiple steps.
Additionally, the processor may be coupled to buttons or some type of user interface. In such instances, user preferences may, in part, dictate the output of the device. For example, if the user inputs the ambient temperature, the presence of interfering substances in his or her breath, a certain disease state, a certain error tolerance or required specificity, etc, the processor may elect certain algorithms to use in the analysis of the data received.
The output of the processing device or the thermopile can be quantitative or qualitative, depending on the application, use, design objectives, etc. For example, an acetone sensor designed for pediatric patients may be equipped with colored indicators that correlate with the seriousness of diabetic ketoacidosis. However, for physicians, the exact concentration of acetone may be displayed.
Having described the basic components of illustrative sensor 2, an illustration of a preferred implementation of a method for its operation in accordance with another related aspect of the invention will now be described. With reference to FIG. 1, a user 1 blows into mouthpiece 3. The breath passes through the mouthpiece 3 into gas collecting device conduit 4 where thermal sensor 5 comprising thermopile 8 is located. The analyte in the breath diffuses to or otherwise contacts the surface of sensor 5 where it contacts the analyte interactant 6 and reacts with it in an enthalpic process. The heat generated or consumed from this process is transferred through substrate 7 to the sensing junctions of thermopile 8, thereby raising or lowering the temperature of the sensing junctions. This heat generation or consumption causes a temperature difference between the sensing and reference junctions of thermopile 8, thereby producing a change in the voltage produced by the thermopile 8 and thus the sensor 5. This voltage therefore comprises a signal representative of the thermal energy change associated with the enthalpic reaction. Stated differently, the output voltage is proportional to the temperature difference between the junction sets, which temperature difference is related to the heat generated or consumed by the analyte interactions, which in turn is related to the amount of the analyte present in the gas. The thermopile 8 is typically thermally insulated from the ambient by a suitable insulator 9, and therefore the signal represents an accurate measurement of the thermal energy change associated with the analyte-analyte interactant reaction. From this signal and the embodied thermal energy change, an assessment may be made as to whether the analyte-analyte interactant reaction involved acetone as the analyte. It also may be used to assess the amount and/or concentration of the acetone analyte in the gas stream.
Generally speaking, the reference junctions compensate for changes in the temperature of the gas stream. If the reference junction temperature were fixed by placing the junctions over a heat sink or insulating them, for example, then a non-interaction effect such as a change in the gas stream temperature would cause a temperature difference between the reference and sensing junctions. In medical applications, this typically is a concern. When the breath expired by the patient passes over the sensor, the thermopile will experience a non-interaction based temperature change merely due to the fact that expired breath is close to body temperature which is close to 37° C. If the sensor is originally contained in an environment which is at 37° C., this may not be an issue. If the thermopile was at room temperature originally and the temperature of the reference junctions was fixed, then the sensor would register a voltage that is proportional to a temperature change between body and room temperature. However, if both the reference and sensing junctions are exposed to the gas stream, then the thermopile will register a temperature change of zero because of the thermopile's inherent common mode rejection. This common mode rejection ratio is a property of thermopiles that operate differentially.
FIG. 38 shows an embodiment of a simple pyroelectric chemical sensor. In it, the pyroelectric material 273 is sandwiched between two electrodes 272. One of the electrodes 272 is coated with an analyte interactant 274. The analyte 275 is transferred to the analyte interactant 274 where an enthalpic interaction occurs that transfers heat to the sensor. This sensor may be placed in a flow chamber 270 with insulation 271.
The phenomenology and characteristics of the gas flow can impact the operation of analyte sensing devices such as sensor 2. The details of the gas flow can influence a number of factors bearing upon the operation of the device, for example, such as local concentrations of analyte, particularly at the interface between the analyte and the analyte interactant (the “analyte-analyte interactant interface”), where the analyte-analyte interactant reactions occur or are initiated, the local temperature at the analyte-analyte interactant interface, the formation and existence of boundary layers or fluid layers that can influence diffusion of analyte to the interface, the diffusion of reaction products away from the interface, the diffusion of thermal energy away from the interface, etc., the residence time of the gas and thus the analyte at the analyte-analyte interactant interface, and others. Therefore, the design and performance of such analyte sensing devices can be improved through careful consideration of these flow characteristics.
Flow properties can be affected in a number of ways, including but not limited to such things as the design of the gas input, the gas collecting device, the thermal sensor device, and the interaction of the various components. The conduit 4, for example, may be cylindrical, rectangular or any of a variety of shapes that allow the analyte to reach the thermal sensor 5. The mouthpiece 3 may be detachable and replaceable. Alternately the conduit 4 may be as narrow as the mouthpiece 3. For situations in which the analyte is transferred to the thermopile or pyroelectric 8 purely or predominantly by diffusion, the conduit 4 may comprise an overlying shelter to protect the sensor from particles such as dust.
The gas can come into contact with the thermal sensor in various ways. These various ways can impact the flow regime of the gas. When a fluid comes into contact with a surface, there is a no-slip boundary condition and the velocity at the surface is therefore zero or essentially zero. The velocity therefore varies between zero and the bulk velocity. The distance between the surface and the point at which molecules are traveling at 99% of the bulk velocity is known as the “hydrodynamic boundary layer.” As the distance from the leading edge of the surface increases, the thickness of the hydrodynamic boundary layer increases. If the fluid is passing through a conduit, the hydrodynamic boundary layer is limited by the dimensions of the conduit such as the height or diameter.
If the surface is coated with a chemical, such as an analyte interactant, then a concentration boundary layer for the analyte will form. As with the hydrodynamic boundary layer, the thickness of the concentration boundary layer for the analyte will increase as a function of distance from the leading edge. Therefore, the flux to the surface of the analyte decreases rapidly along the length of the conduit with maximum flux occurring at the leading edge. The diminishing flux can be an advantageous consideration if it is necessary to react the analyte with a chemical, such as the analyte interactant, that is immobilized at the surface.
One way to increase the flux of analyte at and to the surface is to interrupt the growth of the concentration boundary layer. If the analyte interactant is immobilized in a discontinuous fashion such that the interactant is immobilized for a certain distance and followed thereafter by some degree of interruption, then the concentration boundary layer thickness will decay. The interruption may include but is not limited to a non-reactive surface of the same or a greater distance as the adjacent region of analyte interactant. Thereafter, if analyte is present at the surface, the concentration boundary layer will begin to grow again. In this way, the flux of analyte to the surface can be maintained relatively high at each point where there is analyte present. Using this manner of chemical patterning, the flux to the surface of analyte can greatly surpass the flux that would be achieved if the entire surface had been coated with interactant without such interruptions and discontinuities.
There are other ways by which the concentration boundary layer can be interrupted. For example, if the fluid flow changes direction, then both the hydrodynamic and concentration boundary layers will be interrupted. This could happen using a coiled flow path.
Another way to interrupt the concentration boundary layer is to place an obstruction immediately following the immobilized chemical. This obstruction would force the streamlines to change direction and therefore cause turbulence. The boundary layers would reform when the fluid comes in contact with a smooth surface.
Another way to interrupt the concentration boundary layer is to immobilize chemical throughout the chamber, but to inactivate the chemical at the appropriate locations. For instance, if the chemical can be inactivated by exposure to UV light, an appropriate photo-mask can be designed to achieve this.
Preferably, but optionally, the flow of the gas is directed in such a way that all of the analyte in the entering gas stream flows over the junctions of the thermopile or over the pyroelectric device. In this way, fluid flow over the legs of the thermopile between the sensing and reference junctions can be minimized. This is particularly relevant when a bolus of fluid is injected into or exposed to the sensor 2, in which case the number of molecules available for reaction is limited.
The sensor 2 and more specifically the arrangement of the gas collecting device and the analyte interactant may be disposed so that the analyte diffuses from the gas to the analyte interactant wherein the thermal energy is readily transferred to the thermal sensor 5. The design also may be such that the analyte is convected directly to the analyte interactant. The sensor 2 also may be configured so that the analyte is convected across the analyte interactant and diffusion also occurs to bring the analyte in contact with the analyte interactant.
The thermopile device preferably is insulated, and more preferably it is insulated with the metals facing the insulation and the substrate left exposed. On the substrate and over the legs of the thermopile device, barriers are created, wherein the barriers can serve as channel walls by which to direct fluid flow over the thermopile junctions (both reference and sensing). The placement of the channel walls over the legs of the thermopile in presently preferred embodiments does not affect the signal as the thermopile response is proportional to the change in temperature between the reference and sensing junctions, and not any intermediate temperature differentials.
In a preferred embodiment and particularly if the surface reactions are highly exothermic, the channels can be created such that the reference junctions are contained within channels disparate from those containing the sensing junctions. A possible advantage of this embodiment is that lateral heat transfer from the sensing to reference junctions will be minimized. Additionally, if the channels are designed in such a way that the reference junction channels are positioned at the start and end of the entire flow path, the temperature compensation is improved. In other words, the fluid flowing over the sensing junctions may experience an increase in temperature due to the convective heat transfer. Therefore, it is possible that the temperature of the gas will increase as a function of distance through the channels. In this case, therefore, it is desirable that the reference junctions exist at the start and end of the flow path.
In a preferred embodiment, the sensing and reference junctions are placed in an alternating fashion along the length of the conduit as shown, for example, in FIG. 20. This may be useful if the flow conditions are such that turbulent flow is expected. In this case, both the sensing and reference junctions would experience the same effect which would help to reduce the effect of thermal noise which may be higher than normal under turbulent flow conditions due to the presence of fluid eddies, etc.
The analyte interactant may be deposited immediately after the leading edge. Assuming an instantaneous reaction, the flux of analyte to the surface is directly proportional to the bulk concentration and square root of the distance from the leading edge and inversely proportional to the square root of the velocity. Immobilizing analyte interactants over large length of the sensor thus becomes inefficient at some point.
In one embodiment, there is a thermal sensor at the top and bottom of the conduit. The thermal sensor at the top and the one at the bottom will both have some chemical (e.g. analyte interactant) immobilized and the fluid will be exposed to both devices. There will be analyte flux (mass transfer) to both the top and bottom devices which will at least double the signal.
In another embodiment, the entering flow stream is divided and directed over a different set of electrically coupled reference and sensing junctions. In this way, the velocity over the immobilized chemical will be less. As the velocity decreases, the analyte has more time to diffuse to the surface as diffusion transport will dominate over convection transport.
The design details of the thermopile or pyroelectric 8 can vary, and can be optimized to meet different applications or design objectives. FIGS. 1 and 2 show examples of different thermopile geometries, i.e., rectangular and circular. The rectangular embodiment may be preferred in situations where, for instance, there is flowing gas over the thermopile. The energy consumed or generated at the sensing junctions can be convected downstream instead of to the reference junctions. In the latter case, the signal would be slightly masked. The circular embodiment may be preferred in systems, for example, where the interactant is best immobilized as a droplet or other spherical form. Additionally, the circular geometry provides symmetry to the device where the reference junctions are all equally distributed from the enthalpic process. In these embodiments, the cumulative voltage generated by the individual thermocouples is measured at the thermopile contact pads. To reiterate, however, many different geometries may be used including, for example, those shown in FIG. 19 and FIG. 20.
Multiple thermal sensors may be linked in arrays. Several thermal sensors can have the same interactant to detect the same analyte. Their electrical outputs (voltage, current, etc) could be averaged by a microprocessor with the result that net effect of noise is reduced. Alternatively, the various thermal sensors may be connected in series and the net output transmitted to a microprocessor. Alternatively, each of several thermal sensors may be coated with a different interactant so as to more selectively detect an analyte.
The thermal sensor device can be integrated within a microfluidic gas analysis device. Microfluidic devices have gained significant interest recently due to their ability to perform multiple processes in very short time intervals and in very little space. The thermopile and pyroelectric device are well suited for use in a microfluidic gas analyzer because they are easily miniaturized.
Preferably but optionally, both the reference and sensing junctions of the thermopile device are coated with a non-interactive substance (with respect to the analyte) that helps to equalize the thermal load on both of these junction sets. For example, if an enzyme such as alcohol dehydrogenase is entrapped within a gel matrix, the gel matrix without the enzyme might be placed on the reference junctions and that gel containing the enzyme on the sensing junctions. In another case, both the reference and sensing junctions are coated with a substance like silicone grease. Over the sensing junctions, the silicone grease adheres interactants that are in particle form, such as trichloroisocyanuric acid.
Optionally, the reference junctions may be coated with an interactive substance that is different from the analyte interactant that is placed on the sensing junctions. A configuration also may be used in which two analyte interactants are used, and wherein the analyte interacts with the first analyte interactant at the reference junction in an endothermic process and with the second analyte interactant at the sensing junction in an exothermic process, or the converse.
Optionally, the legs of the thermopile or that area between the reference and sensing junctions may be coated with an analyte interactant. The heat that is consumed or generated in this area could be transferred to the sensing junctions. The temperature difference between the sensing and reference junctions is proportional to the output voltage of the thermopile.
Modulating the input signal to the pyroelectric sensor may be desirable under certain circumstances. As a first example, while mass transfer of the analyte to the reaction sites will, in most cases, vary with time, thereby producing a time varying temperature signature, it may be advantageous to modulate the signal at a higher frequency rate to enhance the pyroelectric sensor response (e.g. heat stimulation frequency is greater than crystal relaxation frequency).
As a second example, modulation may provide a reference such that the pyroelectric sensor may compare the signal to the “noise” of the environment (e.g. to account for non-specific binding, temperature changes in the fluid, etc).
As these input signals are modulated, the pyroelectric sensor output can be processed to maximize the value of the sensor output. The signal processing unit may include a lock-in amplifier (e.g. to discriminate between signal and noise), chopper-stabilized amplifiers, current amplifiers, charge amplifiers, etc.
The ideal modulation frequency can be determined empirically, theoretically, or by other means. An example of a mathematical model that may be helpful in determining ranges of acceptable modulation frequencies is provided.
In this example, determining an appropriate frequency of modulation can account for three primary factors: (1) the thermal time constant (the relaxation constant of the pyroelectric material), (2) the electrical time constant, and (3) the time for a measurable quantity of the analyte to be transferred to the pyroelectric sensor surface (mass transfer limitations).
The thermal and electrical time constants, τthermal and τelectrical respectively, are:



  
    
      f
      
        
          
            -
            3
          
          ⁢
          dB
        
        ,
        thermal
      
    
    =
    
      
        1
        
          2
          ⁢
          
            πτ
            thermal
          
        
      
      =
      
        
          1
          
            2
            ⁢
            π
            ⁢
            
              
            
            ⁢
            
              R
              
                T
                ,
                eff
              
            
            ⁢
            
              C
              
                T
                ,
                eff
              
            
          
        
        ⁢
        
          
        
        ⁢
        and
      
    
  




  
    
      f
      
        
          
            -
            3
          
          ⁢
          dB
        
        ,
        electrical
      
    
    =
    
      
        1
        
          2
          ⁢
          
            πτ
            electrical
          
        
      
      =
      
        1
        
          2
          ⁢
          π
          ⁢
          
            
          
          ⁢
          
            R
            E
          
          ⁢
          
            C
            E
          
        
      
    
  



where RT,eff and CT,eff are the effective thermal resistance and capacitance of the pyroelectric sensor and RE and CE are the effective electrical resistance and capacitance of the signal processing interface. To determine the appropriate values for these parameters, we investigate the responsivity (“gain”) of the pyroelectric sensor:





  
    R
    v
  
  =
  
    
      
        v
        0
      
      
        p
        i
      
    
    ∝
    
      
        j
        ⁢
        
          
        
        ⁢
        
          wR
          
            T
            ,
            eff
          
        
        ⁢
        
          R
          E
        
      
      
        
          (
          
            1
            +
            
              j
              ⁢
              
                
              
              ⁢
              
                wR
                T
              
              ⁢
              
                C
                T
              
            
          
          )
        
        ⁢
        
          (
          
            1
            +
            
              j
              ⁢
              
                
              
              ⁢
              
                wR
                E
              
              ⁢
              
                C
                E
              
            
          
          )
        
      
    
  




where Rv is the responsivity, vo is the output voltage, and pi is the input power. Based on the bandpass characteristics and considering the transfer function, the responsivity can be greatest if the modulation (chopping) frequency meets the following constraint for maximum responsivity: 1/τelec<2πfc<1/τthermal where fc is the chopping (modulation) frequency of the thermal input energy. In some cases, the values of the thermal and electrical frequencies are: felectrical=0.1-1 Hz and fthermal=5-35 Hz. Accordingly, as discussed in this example, there is a range of acceptable values for fc. To further constrain this parameter, the time for mass transfer should be considered.

Equation 1 shows a mathematical model that predicts the molar flux of the analyte to the surface of a pyroelectric sensor whereupon analyte interactants that bind specifically to the analyte are immobilized. This model accounts for the unsteady mass transfer of the analyte via convection and two-dimensional diffusion to the immobilized analyte interactant. Equation 1 was derived from the differential form of the mass balance equation (Conservation of Mass):




  
    
      
        
          
            ∂
            u
          
          
            ∂
            t
          
        
        =
        
          
            D
            ⁡
            
              (
              
                
                  
                    
                      ∂
                      2
                    
                    ⁢
                    u
                  
                  
                    ∂
                    
                      x
                      2
                    
                  
                
                +
                
                  
                    
                      ∂
                      2
                    
                    ⁢
                    u
                  
                  
                    ∂
                    
                      y
                      2
                    
                  
                
              
              )
            
          
          -
          
            
              v
              x
            
            ⁢
            
              
                ∂
                u
              
              
                ∂
                x
              
            
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        1
      
    
  




where u is the concentration of the analyte, vx is the velocity profile for the flow conduit, and D is the diffusion coefficient. The chemical kinetics associated with the analyte-analyte interactant interaction were accounted for via a boundary condition as the reaction was heterogeneous in nature. This equation can be solved via numerical methods in a software program such as MatLab using the following explicit formula:





  
    u
    
      i
      ,
      j
      ,
      
        n
        +
        1
      
    
  
  =
  
    
      
        
          αΔ
          ⁢
          
            
          
          ⁢
          t
        
        
          Δ
          ⁢
          
            
          
          ⁢
          
            x
            2
          
        
      
      ⁡
      
        [
        
          
            u
            
              
                i
                +
                1
              
              ,
              j
              ,
              n
            
          
          -
          
            u
            
              
                i
                -
                1
              
              ,
              j
              ,
              n
            
          
        
        ]
      
    
    +
    
      
        
          αΔ
          ⁢
          
            
          
          ⁢
          t
        
        
          Δ
          ⁢
          
            
          
          ⁢
          
            y
            2
          
        
      
      ⁡
      
        [
        
          
            u
            
              i
              ,
              
                j
                +
                1
              
              ,
              n
            
          
          -
          
            u
            
              i
              ,
              
                j
                -
                1
              
              ,
              n
            
          
        
        ]
      
    
    +
    
      
        u
        
          i
          ,
          j
          ,
          n
        
      
      ⁡
      
        [
        
          1
          -
          
            
              αΔ
              ⁢
              
                
              
              ⁢
              t
            
            
              Δ
              ⁢
              
                
              
              ⁢
              
                x
                2
              
            
          
          -
          
            
              αΔ
              ⁢
              
                
              
              ⁢
              t
            
            
              Δ
              ⁢
              
                
              
              ⁢
              
                y
                2
              
            
          
        
        ]
      
    
    +
    
      
        
          βΔ
          ⁢
          
            
          
          ⁢
          t
        
        
          Δ
          ⁢
          
            
          
          ⁢
          x
        
      
      ⁡
      
        [
        
          
            u
            
              
                i
                +
                1
              
              ,
              j
              ,
              n
            
          
          -
          
            u
            
              i
              ,
              j
              ,
              n
            
          
        
        ]
      
    
  




This model is useful in studying implications of the geometry of the flow chamber for such parameters as the surface area for interaction, the distance from the leading edge to the chemical patterning, the velocity characteristics, and the distance for diffusion from the bulk stream.
The mass transfer solution may be coupled to a heat transfer model because the heat generation term is equal to Q(t)=N′′(t)·ΔHr×n where N′′(t) is the time-varying flux of the analyte to the surface of the pyroelectric sensor and ΔHr×n is the heat of reaction. The following heat transfer equation is derived from the principle of Conservation of Energy:




  
    
      
        
          ρ
          ⁢
          
            
          
          ⁢
          
            c
            p
          
          ⁢
          V
          ⁢
          
            
              d
              T
            
            
              d
              t
            
          
        
        =
        
          
            Q
            ⁡
            
              (
              t
              )
            
          
          -
          
            hA
            ⁡
            
              (
              
                T
                -
                
                  T
                  ∞
                
              
              )
            
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        2
      
    
  




From this equation, the surface temperature profile may be derived. The pyroelectric sensor outputs current based on the following equation:




  
    
      
        I
        =
        
          
            p
            ⁡
            
              (
              T
              )
            
          
          ·
          A
          ·
          
            
              d
              T
            
            
              d
              t
            
          
        
      
    
    
      
        Equation
        ⁢
        
          
        
        ⁢
        3
      
    
  




where p(T) is the pyroelectric coefficient, which is a function of temperature, A is the cross-sectional area of the detector element, and dT/dt is the derivative of temperature with respect to time. The temperature differential was computed based on the solution of the energy balance shown in Equation 2.

In this example, based on the operating characteristics of the pyroelectric sensor and circuit, for enhanced signal, the heat input to the pyroelectric sensor should be modulated at some frequency, fc, where felectrical<fc<fthermal. The impact of various values of fc on the mass transfer to the surface and the corresponding output of the pyroelectric sensor should be determined based by, for example, converting the Q(t) term in Equation 2 into a step-wise defined function with frequency fc. If the current output of the pyroelectric sensor, I, has had an opportunity to reach a maximum value within, for example, two-three times the electrical frequency, the particular value of fc may be appropriate. Examples of fc that have been found useful are in the range of 0.5 Hz to 2 Hz. Of course, the frequency of modulation could be greater than or lower than this range of values, depending on the circumstances.
If used correctly, math models can serve as excellent hypotheses for research. Depending on the application, the model can be adapted to, for example, decompose the kinetics parameters to their thermodynamic bases such as bond energies, the Gibbs potential, and other thermodynamic parameters. This may prove useful because when attempting to select analyte interactants, experimentally obtained kinetics parameters may not be readily available and it may be necessary to rely on other properties.
The thermal energy input to the pyroelectric sensor can be modulated or chopped in a number of ways. Various examples are shown hereinafter.
One embodiment of the pyroelectric sensor, shown in FIG. 41, involves switching between a fluid (liquid or gas) that contains the analyte 301 and a second fluid 303 that serves as a reference. This can be done, for example, using electrically controlled valves 302.
Another embodiment of the pyroelectric sensor involves the use of a charged surface 311. If the sensor 310 is used to measure an analyte 312 that is associated with an electrical charge (e.g. proteins that carry a negative charge), then a chargeable surface 311 may be employed. The charge on this surface will be modulated by a control circuit or the like to attract and release the analyte. FIG. 42 exemplifies this via a two stage storyboard.
Another embodiment of a thermal sensor according to an aspect of the invention that uses a pyroelectric sensor involves the use of a magnetic surface 320. Opposite the sensor surface and below the sensor, magnetizable surfaces may be placed. As the magnet is turned on and off, the magnetic beads 322 may move from the sensor surface to the magnetizable surface 320 and vice versa. If the analyte interactant 324 is immobilized on magnetic beads, then the source of binding energy would be modulated from one surface to the other, thereby modulating the sensor signal. An example is shown in FIG. 43.
While these magnetic beads are not limited to any particular embodiment, if the orientation of the bead is advantageous for a given application, then only a point 323 of the bead may be made with a magnetic material.
Another embodiment of the pyroelectric sensor involves the use of a heater 330. The energy required for most binding events is temperature-dependent. Therefore, a heater 330 of known and well characterized behavior may be used to release any analyte bound to the analyte interactant on the surface thereby creating a desorption effect, which can be used to modulate the heat input to the pyroelectric sensor. An example of this embodiment is shown in FIG. 44 via a two-stage storyboard.
Another set of embodiments of the pyroelectric sensor utilize a chemical patterning technique. In these devices, the analyte interactant 344 is patterned in a discontinuous manner on a test strip 343. This test strip 343 is moved across the thermal detector 340 (e.g. the pyroelectric sensing element). When the analyte interactant (Stage 1) is exposed to the fluid, heat may be generated (if the analyte is present), and this heat will be measured by the detector 340. When the portion of the test strip without analyte interactant 345 is exposed to the fluid, there will be no heat generated (or solely noise, interfering signals, non-specific adsorption will be measured). This embodiment is described in FIG. 45 via a two-stage storyboard.
In some cases, the test strip itself may be conductive (e.g. a metallic foil). This way, any heat that is generated by the interaction of the analyte with the immobilized analyte interactant will be conducted efficiently to the thermal detector.
Alternatively, the test strip may be or comprise a pyroelectric ribbon with patterned analyte interactant. If it is a pyroelectric ribbon, the ribbon may be passed over a second thermal detector or it may simply be passed over electrical contacts (e.g. electrical connectors that make contact with the pyroelectric ribbon).
FIG. 55 is a functional block diagram illustrating the configuration of an embodiment of one aspect of the invention that can be used in conjunction with a nanoparticle-based sensor. A user breathes into a fluid collecting device and the sample of breath passes into a first conditioning device containing a moisture-removal function. The sample then passes into a second conditioning device containing an analyte-retaining sorbent material. The analyte is thus retained in the second conditioning device while the remainder of the sample of breath passes over the heated sensor element and then exits the breath analysis device. The second conditioning device is then isolated from the flow path and heated. Carrier gas is allowed to pass over the second conditioning device, removing the analyte from the second conditioning device and directing it over the sensing device comprising a nanoparticle-based sensor, which may include a single element or an array. Changes in the characteristic/s of the sensing device are then transmitted to a microprocessor for analysis, data logging, storage, and/or transmission.
FIG. 56 is an embodiment that utilizes two conditioning devices and a nanoparticle-based sensor. In this embodiment, a user blows into the fluid collecting device through a check valve. The sample of breath passes through a first sample conditioning device and then through a second sample conditioning device. The breath sample then passes through a 3-way valve, then through a flow restrictor, and exits the breath analysis device. The resistance to breath flow is controlled by the packing density of the two sample conditioning columns and the flow restrictor. The fluid resistance is set by the flow restrictor to allow comfortable and rapid sampling of the users' breath. Once the sample has been dehumidified by the first sample conditioning device and trapped into the second sample conditioning device, the second sample conditioning device is then isolated by the three-way valve. A carrier gas valve is opened, which then bypasses the second sample conditioning device and is then directed to flow over the sensing device and to exit the device. The system thus collects baseline sensor data, showing the electrical resistance changes with time for a sample with no analyte. While the carrier is bypassing the second conditioning device, the second conditioning device is being heated. Once the appropriate temperature is reached, the valves are switched to pass the carrier gas through the second conditioning device and onto the sensing device. The analyte in the gas stream interacts with the sensing device in a manner that is reproducible and dependent on the concentration of the analyte released from the second conditioning device.
Such an apparatus may be used to sense acetone in breath. In this embodiment, a mouthpiece is coupled to a first conditioning device comprised of a desiccant material within a flow conduit or chamber, wherein the flow conduit or chamber may be under thermal control whereby the desiccant material may be heated and/or cooled. The desiccant material is calcium chloride (200 mg). A second conditioning device is positioned downstream of the first conditioning device and consists of a sorbent material within a flow conduit or chamber, preferably Tenax TA (250 mg). The second conditioning device is under thermal control whereby the sorbent material may be heated and/or cooled. A disposable gas cylinder or alternative gas source (such as a pump utilizing ambient air) is connected to the flow circuit by a one-way valve, and automated 3-way valves allow computer-controlled direction of the gas streams within the acetone-sensing device. A user blows into the mouthpiece, whereby the exhaled breath gases pass through the desiccant held at 40 deg C. and into the sorbent trap held at 30 deg C. Exhaled moisture is thus first captured into the desiccant material and the residual moisture passes through the sorbent material. Acetone is retained in the sorbent material. The second conditioning device is then isolated from the flow path using two 3-way valves and the sorbent material is heated to 85 deg C. The one-way valve is then opened to allow passage of gas from the disposable cylinder or alternate gas source over the nanoparticle-based sensor, bypassing the sorbent trap. The gas in the cylinder comprises 21% v/v oxygen in a balance of nitrogen, charged with a set pressure to allow flow from the cylinder to be repeatable for each replacement of the cylinder. The nanoparticle-based sensor is operated with the nanoparticle material held at 160 deg C. The gas from the disposable cylinder flows over the nanoparticle-based sensor and creates a baseline signal, which is logged by a microcontroller. Once a sufficient baseline has been logged and the second conditioning device containing the sorbent material has attained a temperature of 85 deg C., the 3-way valves are actuated to put the second conditioning device in-line with the flowing gas stream of a known composition. Acetone is thus swept out of the sorbent material and over the nanomaterial sensing element. A first deflection in the sensor signal trace is due to the flow artifact created by the switching of the valves, but the second deflection in the sensor signal trace has a magnitude of deflection that is proportional to the acetone fraction in the breath sample. The acetone displaces oxygen in a chemical reaction occurring at the nanomaterial surface and this causes a decrease in the resistance of the nanomaterial. A circuit comprising a low current constant current source and high input impedance voltmeter measures the change in resistance and this change corresponds to the concentration of acetone in the sample. The nanoparticle-based sensor is comprised of gamma-phase ferric oxide (Fe2O3) nanoparticles manufactured using a sol-gel process with an average particle diameter of 20 nm. The nanoparticles are disposed on a planar alumina substrate onto screen-printed gold contacts which are in electrical communication with screen printed silver lead traces. The nanoparticle material is deposited over the gold contacts, bridging a 1 mm electrode gap. The nanoparticle material is approximately 150 micrometers thick, 2 mm wide, and 3 mm long.
The apparatus described above can be modified to sense ethanol, isopropanol, or other analytes, in breath. In the case of an embodiment for ethanol sensing, an ethanol-sensitive nanoparticle material is used and the elution parameters are modified. In this embodiment, a mouthpiece is coupled to a first conditioning device comprised of a desiccant material within a flow conduit or chamber, wherein the flow conduit or chamber is under thermal control whereby the desiccant material may be heated and/or cooled. The desiccant material is calcium chloride (200 mg). A second conditioning device is positioned downstream of the first conditioning device and consists of a sorbent material within a flow conduit or chamber, preferably Tenax TA (250 mg). The second conditioning device is under thermal control whereby the sorbent material may be heated and/or cooled. A disposable gas cylinder or suitable alternative gas source such as a pump in communication with ambient air is connected to the flow circuit by a one-way valve, and automated 3-way valves allow computer-controlled direction of the gas streams within the ethanol-sensing device. A user blows into the mouthpiece, whereby the exhaled breath gases pass through the desiccant held at 40 deg C. and into the sorbent trap held at 30 deg C. Exhaled moisture is thus first captured into the desiccant material and the residual moisture passes through the sorbent material. Ethanol is retained in the sorbent material. The second conditioning device is then isolated from the flow path using two 3-way valves and the sorbent material is heated to 50 deg C. The one-way valve is then opened to allow passage of gas from the disposable cylinder over the nanoparticle-based sensor, bypassing the sorbent trap. The gas in the cylinder comprises 21% v/v oxygen in a balance of nitrogen, charged with a set pressure to allow flow from the cylinder to be repeatable for each replacement of the cylinder. The nanoparticle-based sensor is operated with the nanoparticle material held at 200 deg C. The gas from the disposable cylinder or alternative gas source flows over the nanoparticle-based sensor and creates a baseline signal which is logged by a microcontroller. Once a sufficient baseline has been logged and the second conditioning device containing the sorbent material has attained a temperature of 50 deg C., the 3-way valves are actuated to put the second conditioning device in-line with the flowing gas stream of a known composition. Ethanol is thus swept out of the sorbent material and over the nanomaterial-sensing element. A first deflection in the sensor signal trace is due to the flow artifact created by the switching of the valves, but the second deflection in the sensor signal trace has a magnitude of deflection that is proportional to the ethanol fraction in the breath sample. The ethanol displaces oxygen in a chemical reaction occurring at the nanomaterial surface and this causes a decrease in the resistance of the nanomaterial. A circuit comprising a low current constant current source and high input impedance voltmeter measures the change in resistance and this change corresponds to the concentration of ethanol in the sample. The nanoparticle-based sensor is comprised of gamma-phase ferric oxide (Fe2O3) nanoparticles manufactured using a sol-gel process with an average particle diameter of 20 nm doped with 33% w titanium dioxide (TiO2, anatase). The nanoparticles are disposed on a planar alumina substrate onto screen-printed gold contacts which are in electrical communication with screen printed silver lead traces. The nanoparticle material is deposited over the gold contacts, bridging a 1 mm electrode gap. The nanoparticle material is approximately 150 micrometers thick, 2 mm wide, and 3 mm long.
The apparatus is not limited to sensing a single analyte. Two-analyte sensing capacity of a nanoparticle-based sensor can be achieved, e.g., using the general components as described above for acetone and isopropanol sensing, but using a two-step elution procedure and both acetone and isopropanol-sensitive nanoparticle-based sensor materials. In this case, a mouthpiece is coupled to a first conditioning device comprised of a desiccant material within a flow conduit or chamber, wherein the flow conduit or chamber is under thermal control whereby the desiccant material may be heated and/or cooled. The desiccant material is calcium chloride (200 mg). A second conditioning device is positioned downstream of the first conditioning device and consists of a sorbent material within a flow conduit or chamber, preferably Tenax TA (250 mg). The second conditioning device is under thermal control whereby the sorbent material can be heated and cooled. A disposable gas cylinder or suitable alternative gas source such as a pump in communication with ambient air is connected to the flow circuit by a one-way valve, and automated 3-way valves allow computer-controlled direction of the gas streams within the two-analyte sensing device. A user blows into the mouthpiece, whereby the exhaled breath gases pass through the desiccant held at 40 deg C. and into the sorbent trap held at 30 deg C. Exhaled moisture is thus first captured into the desiccant material and the residual moisture passes through the sorbent material. Acetone and ethanol are retained in the sorbent material. The second conditioning device is then isolated from the flow path using two 3-way valves and the sorbent material is heated to 50 deg C. The one-way valve is then opened to allow passage of gas from the disposable cylinder or an alternative gas source over the nanoparticle-based sensor, bypassing the sorbent trap. The gas in the cylinder or the ambient air comprises 21% v/v oxygen in a balance of nitrogen, charged with a set pressure to allow flow from the cylinder to be repeatable for each replacement of the cylinder. A first nanoparticle-based sensor for isopropanol is operated with the nanoparticle material held at 200 deg C. A second nanoparticle-based sensor for acetone is operated with the nanoparticle material held at 160 deg C. The gas from the disposable cylinder or alternative gas source flows over the nanoparticle-based sensors and creates baseline signals which are logged by a microcontroller. Once a sufficient baseline has been logged and the second conditioning device containing the sorbent material has attained a temperature of 50 deg C., the 3-way valves are actuated to put the second conditioning device in-line with the flowing gas stream of a known composition. Isopropanol is thus swept out of the sorbent material and over the nanomaterial sensing element. A first deflection in the sensor signal trace is due to the flow artifact created by the switching of the valves, but the second deflection in the sensor signal trace has a magnitude of deflection that is proportional to the isopropanol fraction in the breath sample. The isopropanol displaces oxygen in a chemical reaction occurring at the nanomaterial surface and this causes a decrease in the resistance of the nanomaterial. A circuit comprising a low current constant current source and high input impedance voltmeter measures the change in resistance and this change corresponds to the concentration of isopropanol in the sample. The second conditioning device is then re-isolated using the 3-way valves, and the sorbent material is heated to 85 deg C. Once the temperature has been obtained, the 3-way valves open to allow the carrier gas to displace the acetone from the sorbent, which then passes over the two sensors. As each sensor is sensitive in varying degree to both analytes, the sensor signals from both sensors are used to infer the concentration of both analytes in the sample. The acetone nanoparticle-based sensor is comprised of gamma-phase ferric oxide (Fe2O3) nanoparticles manufactured using a sol-gel process with an average particle diameter of 20 nm. The isopropanol nanoparticle-based sensor is comprised of gamma-phase ferric oxide (Fe2O3) nanoparticles manufactured using a sol-gel process with an average particle diameter of 20 nm doped with 33% w titanium dioxide (TiO2, anatase). The nanoparticles are disposed on a planar alumina substrate onto screen-printed gold contacts which are in electrical communication with screen printed silver lead traces. The nanoparticle material is deposited over the gold contacts, bridging a 1 mm electrode gap. The nanoparticle material is approximately 150 micrometers thick, 2 mm wide, and 3 mm long.
FIG. 57 is an embodiment of a hand-held breath gas analyzer with a sensing device, preferably a nanoparticle-based sensor. This hand-held embodiment of the breath gas analyzer is comprised of electronically-actuated valves, a first conditioning device embedded in a disposable mouthpiece, a second conditioning device, a two-element nanoparticle-based sensor array, a disposable/rechargeable compressed gas cylinder, fluidic interconnect components, a user display screen, and interface buttons. The battery pack, positioned on the top piece adjacent to the user display, is rechargeable.
A conditioning device is any apparatus that is configured to condition the sample of breath for sensing by the sensing device. The conditioning device may condition the sample of breath for temperature, humidity, flow rate, pressure, concentration, or some combination thereof.
Parameters like temperature, gas water vapor content, and flow rate may significantly impact the ability of chemical sensors to reproducibly sense the concentration of an analyte. One way that we have addressed this problem is using a conditioning device. Constructing conditioning devices that are conducive to hand-held breath analyzers is challenging. Even if conditioning devices would be constructed by simply miniaturizing laboratory equipment, this may not be a practical solution because of the cost associated with laboratory control equipment like mass flow controllers, dehumidifers, etc.
Before addressing specific embodiments that we have developed, it may be useful to describe the substantial challenges that we have had to overcome. Focusing on just one breath-specific problem that we have addressed, human exhaled breath gas contains a large amount of water vapor, and semiconducting nanoparticles are, in general, highly sensitive to moisture content of the gas sample. In low-level analyte detection, which is the case for breath gas analysis, water vapor can obscure the sensor's response to the analyte, either completely destroying the ability of the sensor to respond to the analyte of interest or deteriorating its performance significantly.
Addressing the moisture level of breath samples is challenging because the water vapor content of breath is a relatively large portion of the total content. Compared to analytes of interest which may have concentrations in the parts per billion or low parts per million, water vapor content in exhaled human breath is measured in the parts per hundred. When a chosen sensor technology shows sensitivity to water vapor, it may be necessary to both drastically reduce water vapor content in a sensed gas stream while simultaneously retaining a sufficient portion of the analyte of interest. Furthermore, the elevated temperature of exhaled human breath compared to common ambient room temperatures means that the water vapor in exhaled breath will likely condense. Condensation in flow circuits, electrical systems, and onto sensor elements or gas processing components can complicate a sensing system significantly. Many analytes of interest will be attracted to liquid water such that condensation will also affect the amount of analyte that reaches the detector.
FIG. 58 shows three embodiments of conditioning devices that condition a sample of breath for humidity.
Embodiment A of FIG. 58 is a disposable mouthpiece packed with desiccant material. This packed desiccant mouthpiece is sealed in foil; for use, the user places the mouthpiece into the housing of the sensing device, which punctures the bottom seal. The user removes a foil seal from the top, and the device is ready to be blown into.
Embodiment B of FIG. 58 is a gas exchange module utilizing semi-permeable membranes and the cross-flow of dry gases. For the cross-flow designs, user breath is passed through a bundle of parallel water permeable fibers. Cross flow is created using on-board pumps, disposable compressed gas cylinders, or fans in communication with the ambient air.
Embodiment C of FIG. 58 utilizes diffusion barriers based on semi-permeable membranes. Depending on the properties of the membrane (e.g., thickness, diffusivity, etc.), this embodiment may reduce the overall response time.
The conditioning device may comprise a sorbent trap. The sorbent trap may be or comprise one of a porous organic polymer (such as 2,6-diphenylene oxide “Tenax TA”, 2,6-diphenylene oxide and graphite “Tenax GR”, “Chromosorb” or “Porapak”), a graphitized carbon black (such as “Carbotrap”, “Carbopack”, “Carbograph”), a carbon molecular sieve (such as “Spherocarb”, “Carbosieve”, “Carboxen”, molecular sieve 3A, 4A, 5A, 13X, etc., “Unicarb”), a carbon nanotube device or other nanostructured carbon, or any other activated carbon or adsorbent resin (such as XAD-2 “Amberlite” and “Anasorb CSC”).
The conditioning device may comprise a humidity extraction device. The humidity extraction device may be or comprise calcium dichloride (CaCl2), magnesium perchlorate (Mg(ClO4)2), magnesium carbonate (MgCO3), lithium chloride (LiCl), potassium carbonate (K2CO3), copper (II) sulfate (CuSO4), calcium sulfate (CaSO4), oxobarium (BaO), phosphorous pentoxide (P2O5), zeolite, silica gel, aluminum oxide (Al2O3), or molecular sieve. In certain embodiments, the humidity extraction device is disposed atop the sensing device and it comprises a water impermeable membrane. In other instances, the humidity extraction device is disposed upstream of the sensing device and it comprises a water permeable membrane that is in fluidic contact with a stream of dry fluid.
The conditioning device may be or comprise a flow regulation device. The flow regulation device may be configured to condition the sample of breath such that the sample is at the constant flow rate. But, it may also ensure that the sample of breath is at a predetermined flow rate, which may vary with time. For example, certain chemical systems have an amplification process, whereby the sensitivity of the sensor increases with increased exposure to an analyte. For such a system, the flow regulation device may allow for increased mass transfer of the analyte during the initial phase of the chemical reaction and then gradually decrease mass transfer of the analyte as the chemical amplification process occurs.
The conditioning device may be or comprise one of a heater or a cooler. It may also be a second sensing device that senses an interfering substance. The information from the second sensing device may be used by the processing device to characterize the analyte. The conditioning device may be or comprise a concentrator.
The conditioning device may be disposable. In certain embodiments, it may be desirable to package the conditioning device in a sterile package. Accordingly, the breath analyzer may contain an insertable mechanism that is configured to allow for the conditioning device to be inserted, removed, and either replaced or replenished. For example, if the conditioning device is in the form of embodiment A of FIG. 58, the insertable mechanism may be a snap-on piece between the mouthpiece and the rest of the remainder of the breath analyzer.
The sensing device may be or comprise any type of sensor or transducer capable of performing the functions for the sensor generally described herein. The sensing device may be or comprise a chemical sensor and/or it may be or comprise other types of sensors, such as flow sensors.
The sensing device may be or comprise any one of the following, or a combination thereof: an absorbance spectrometer, an amperometer, an enzyme-based sensor, a capacitance sensor, an impedance spectrometer, an acoustic impedance spectroscopy device, a thermoelectric sensor, a fuel cell, a colorimetric sensor, a fluorescence-based sensor, a phosphorescence-based sensor, a chemiluminescence-based sensor, and a bioluminescence-based sensor.
The colorimetric sensor may be or comprise a reflectance sensor, an absorbance sensor, a scatter-based sensor, and a spectroscope. The fluorescent-based sensor may be or comprise a device that is configured to operate based on changes of at least one of quenching, excitation or emission peak changes, and lifetime changes. The phosphorescence-based sensor may be or comprise any device that is configured to operate based on at least one of quenching, excitation or emission peak changes, and lifetime changes. The chemiluminescence-based sensor may be or comprise any device that is configured to operate based on at least one of quenching, excitation or emission peak changes, and lifetime changes. The bioluminescence-based sensor may be or comprise any device that is configured to operate based on at least one of quenching, excitation or emission peak changes, and lifetime changes. The enzyme-based sensor may be or comprise an electrochemical sensor using an enzyme mix comprising a NADPH-dependent secondary alcohol dehydrogenase (such as from Thermoanaerobium brockii), malic dehydrogenase, and pyruvate oxidase. The enzyme mix and electrochemical sensor may also include any embodiments described in U.S. Pat. No. 7,364,551, which is incorporated herein by reference.
Preferably, the sensing device comprises a nanoparticle-based sensor. A nanoparticle-based sensor is comprised of a nanomaterial coupled to an electrode. The term nanomaterial as used herein is used broadly. It includes analyte-responsive materials or elements which have been synthesized in such a fashion such that the majority of individual particles or fundamental units have characteristic dimensions (i.e., spherical diameter for spheres, cross-sectional diameter for nanotubes, etc.) within the range of a few nanometers to several tens of nanometers, which are deposited onto a substrate (as thick-films, self-assembled lawns, etc.). Nanomaterial, as used herein, may also include substances whose individual particle dimensions are outside of the “nano” specification above, but which are nevertheless formulated into a paste, film, or other sensitive layer and adhered to a substrate in contact with electrodes. Examples of nanomaterials that may be used include pure substances (iron III) oxide (Fe2O3), tungsten (VI) oxide (WO3), titanium (IV) oxide (TiO2), molybdenum (VI) oxide (MoO3), vanadium (V) oxide (V2O5), chromium (III) oxide (Cr2O3), indium (III) oxide (In2O3), tin (IV) oxide (SnO2), manganese (IV) oxide (MnO2)), pure substances of specific crystalline structure (monoclinic, orthorhombic, cubic, etc.), pure substances of specific solid phase (alpha, beta, gamma, epsilon, etc.), pure substances with dopants (gamma Fe2O3 doped with TiO2, for example), and substances made with specific synthesis methods (sol gel, co-precipitation, ultrasonically assisted co-precipitation, flame spray pyrolysis, etc.), and substances formed with specific nanocrystalline structures (nanoparticles, single-walled nanotubes, multi-walled nanotubes, single crystal nanowires, nanospheres, nanorods, nanofilms, nanoclusters, etc.).
A nanoparticle-based sensor may comprise a nanomaterial in contact with an electrode material deposited onto a substrate. The nanomaterial may be disposed on the electrode through different means including, without limitation, heat treatment of nanoparticle pastes, drops or powders; low-pressure or vacuum evaporation of pastes, suspensions, or drops; nanoparticle suspensions, self-assembly using gaseous or liquid precursors, etc. This nanoparticle-based sensor may be disposable or it may be reused, depending on the application.
The substrate may be any material which exhibits sufficient adhesion to the nanomaterials and electrode materials of interest, as well as any other physical parameter of interest such as stability under the temperature regime required for sensor operation or mechanical rigidity. Substrates may include ceramics such as alumina (Al2O3), glass, or thermally-stable plastics such as polyimide.
FIG. 59 is a top view of an embodiment of a nanoparticle-based sensor. In this embodiment, nanoparticle pastes can be applied onto substrates with suitable temperature resistance and mechanical rigidity. Electrical leads can be screen printed onto the substrate, over which the nanomaterial pastes can be applied and cured at high temperatures. A resistance temperature detector trace can also be screen printed onto the substrate, allowing closed loop control of the sensing element's temperature under varying conditions.
The electrode may comprise gold, platinum, nickel, silver, copper, and/or other sufficiently conductive and stable material that performs the function of establishing an electrical coupling between the sensitive area of the nanoparticle sensing material and the electrical readout circuitry. The electrode may have a smooth surface or, for certain applications, it may be designed to have a rough surface that would allow for increased surface area of the nanoparticle sensing material.
FIG. 60 is a bottom view of an embodiment of a nanoparticle-based sensor. In this embodiment, high-resistance heater element traces can be applied on the underside of the sensor chips through screen printing techniques. In this way, heat can be applied directly beneath the sensing element. Leads are spaced so that a single 6-position compression conductor makes contact to both the top and bottom sides simultaneously.
A heater can be deposited onto the electrode near the sensitive element (such as resistive pastes or depositions, screen printed onto the substrate) or placed in its proximity (such as resistive wire wound around the substrate or otherwise placed in proximity to the sensing element). Resistive heating elements can be comprised of any number of materials which exhibit sufficient resistivity, stability, and adhesion to the substrate or positioning scheme, and which exhibit sufficient resistivity, stability, and adhesion appropriate to the operating conditions of the device. Suitable materials may include iron-chrome-aluminum “Kanthal”, nickel, gold-palladium, thick-film epoxy-graphite, and many others. Operating temperature ranges for nanoparticle based devices are commonly in the 100-500 C range but can be outside of this range in more rare circumstances.
The heater can be run open-loop, whereby a constant or pre-defined variable voltage is applied over the heater element, causing current flow which produces heat.
A nanoparticle based sensor may further comprise a temperature sensor and temperature control element located close to the nanoparticle sensing element and may comprise resistive heating wires or traces, resistance temperature devices, thermocouples, control circuitry, and/or other thermal control devices.
The nanomaterial coupled to the electrode may comprise a closed-loop temperature control scheme using a resistance temperature device (RTD), thermocouple, or other heat sensing device working in conjunction with a heater element. Commonly used RTD materials include platinum and nickel but can include any material that exhibits repeatable resistivity changes as a function of temperature, sufficient resistivity change within the temperature range of interest, and suitable adhesion or fixation properties. Thermocouple elements or other temperature sensing devices can also be used to close the control loop and the methods of manufacture and deployment are both varied and well known. In certain embodiments, closing the loop on thermal control creates a nanoparticle-based sensor that operates more repeatably within a tightly confined temperature range.
The sensing device may be a nanoparticle-based sensor coupled to another type of sensor, such as a thermoelectric sensor or an electrochemical sensor. A combination-sensing device of this nature may allow for the measurement and/or analysis of more analytes in breath than any single sensing device or even an array of any single type of sensing device. One example may be an electrochemical sensor for analysis of breath acetone coupled to a nanoparticle-based sensor for analysis of breath oxygen. Or, the sensing device may comprise multiple nanoparticle-based sensors.
The change is sensed by the sensing device and comprises information useful in characterizing the analyte. The change may be or comprise any reproducible shift in at least one of resistance, conductance, capacitance, impedance, inductance, thermal energy, thermal conductivity, optical properties, acoustic properties. In a preferred embodiment using a nanoparticle-based sensor, the change is a shift in resistance.
The information useful in characterizing the analyte may be used to determine a treatment protocol. The treatment protocol may involve dispensing a medication, altering the dosage of a medication, suggesting a dosage change for a medication, or providing motivational feedback.
In devices suitable for consumer applications and the like, it is often desirable to have disposable components. Test strips may also bypass the problem of replacing the analyte interactant.
In such cases, it is possible that the user would input the test strip. An internal device component (e.g. gear with gear belt) could drive the test strip across the thermal sensor. Of course, there are a variety of other mechanisms by which the test strip could be moved across the sensor in the desired fashion.
If there is concern that the analyte will have insufficient time to diffuse to the test strip, a control valve 350 such as shown in FIG. 46 may be used. If desirable, a mixer 351 may also be used to facilitate mass transfer to the analyte interactant.
The test strip is not limited to any particular geometry. FIG. 47 shows an example of a test strip that is circular. In this embodiment, the analyte 360 enters a conduit 361. The conduit 361 is open to the test strip 366 in a zone 362. The test strip 366 rotates via some rotational mechanism 364 such that the part of the test strip that is present in the zone alternates between depositions of analyte interactant 363 and some non-interacting reference species 365.
Another embodiment utilizes a mechanical chopper. This mechanical chopper can be of any particular shape. In FIG. 48, it is shown in a circular design. The mechanical chopper 371 will have “holes” 372 that allow for heat to pass through. An example of such an embodiment is shown in FIG. 48. In this embodiment, heat generated from an interaction between the analyte and analyte interactant, which is immobilized on a surface 373 is measured by a thermal detector 370 and the temperature signal is modulated via a mechanical chopper 371.
This mechanical chopper can be used in combination with a packed bed as well. An embodiment that utilizes this principle is shown in FIG. 49.
The enthalpic process occurs due to the interaction of the analyte and the reactive analyte interactant substance(s). The analyte interactant can produce or consume heat by any of a variety of ways, including but not limited to chemical reaction, catalysis, adsorption, absorption, binding effect, aptamer interaction, physical entrapment, a phase change, or any combination thereof. Biochemical reactions such as DNA and RNA hybridization, protein interaction, antibody-antigen reactions also can be used to instigate the enthalpic process in this system.
Aptamers are specific RNA or DNA oligonucleotides or proteins which can adopt a vast number of three dimensional shapes. Due to this property, aptamers can be produced to bind tightly to a specific molecular target. Because an extraordinary diversity of molecular shapes exist within the universe of all possible nucleotide sequences, aptamers may be obtained for a wide array of molecular targets, including most proteins, carbohydrates, lipids, nucleotides, other small molecules or complex structures such as viruses. Aptamers are generally produced through an in vitro evolutionary process called “systematic evolution of ligands by exponential enrichment” (SELEX). The method is an iterative process based on selection and amplification of the anticipated tight binding aptamer. The start library for selection of aptamers contains single stranded DNA oligonucleotides with a central region of randomized sequences (up to 1015 different sequences) which are flanked by constant regions for subsequent transcription, reverse transcription and DNA amplification. The start library is amplified by PCR and transcribed to an RNA start pool by T7 transcription. Target specific RNA is selected from the pool by allowing the pool to interact with the target molecule, only tight binding RNA molecules with high affinity are removed from the reaction cycle, the tight binding RNA molecules are reverse transcribed to cDNA and amplified to double stranded DNA by PCR. These enriched binding sequences are transcribed back to RNA which is the source for the next selection and amplification cycle. Such selection cycles are usually repeated 5-12 times in order to obtain only sequences with highest binding affinities against the target molecule.
Interactants can be or comprise adsorbents including but not limited to activated carbon, silica gel, and platinum black. Preferably, the adsorbent can be impregnated with another species that reacts with the analyte following the adsorption. While analyte interactants may be or comprise adsorbents or absorbents, as may be appreciated, they are not limited to them.
Interactants also can be or comprise chemicals or chemical reactants. Suitable chemicals that interact with acetone include but are not limited to halogenated compounds, sodium hypochlorite, hypochlorous acid, sodium monochloroisocyanurate, sodium dichloroisocyanurate, monochloroisocyanuric acid, dichloroisocyanuric acid, and trichloroisocyanuric acid. Alcohol can interact with a chemicals such as chromium trioxide (CrO3) or enzymes such as alcohol dehydrogenase, alcohol oxidase, or acetoalcohol oxidase. Other reactants may be or comprise chloroform, chloroform in the presence of a base, and nitrosyl chloride.
Optionally, the interactant may not directly interact with the analyte, but a byproduct of the interactant and some other compound in the gas can product a different interactant with which the analyte reactants. A possible reason for selecting such an interactant is for stability; thus, if the true analyte-interacting species is unstable under the particular operating conditions, then it may be desirable to select a more stable interactant that, upon exposure to the analyte or some other substance present in the gas containing the analyte, produces a different analyte interactant. For example, trichloroisocyanuric acid can react with water to form hypochlorous acid, which engages in an enthalpic reaction with acetone.
Vapor phase reactions are sometimes limited because reactions in aqueous solution typically involve acid or base catalysis. Therefore, in the vapor phase, the presence of a catalyst or an activating agent, such as a protonating agent, can be employed to allow the interactant and analyte to interact.
Optionally, analyte interactants also can be or comprise hydrogenation reagents. For acetone, Raney nickel and platinum catalysts are suitable interactants.
The analyte can also interact with materials from living systems or living systems themselves. Examples include but are not limited to microorganisms, cells, cellular organelles and genetically modified versions thereof. These living systems engage in metabolic processes to sustain life which involve energy exchange and therefore heat consumption or generation. Some chemical analytes such as toxins or pathogens kill or damage cells or impair organelle function. If the living material is immobilized on the sensing junctions of a thermopile, therefore, the change in heat generated or consumed is related to the number of living cells which can be related to the presence of a toxin or pathogen.
Optionally, the interactant may be selected such that the interaction with the analyte involves interaction with other substances in the gas, such as water, oxygen, or another analyte.
While not wishing to be limited to any particular mechanism or theory of operation, the thermal energy change sensed at the thermopile device in some cases may comprise heats of condensation. “Phase change agents” can perform a number of functions relevant to latent heat energy. For example, they can facilitate evaporation and/or condensation. With regard to condensation, they can; alter the surface area such that there is more or less condensation over the sensing junctions than the reference junctions; and promote increased (or decreased) condensation based on the phase change agent's properties, for example, increasing condensation may occur over phase change agents that have a greater polarity. To illustrate this further, a powder is placed on the sensing junctions of thermopile device 8 in sensor 2, thus effectively increasing the surface area over the sensing junctions. Breath containing acetone is passed through a moisture filter and then over the thermal sensor 5. The acetone condenses from the breath onto the surface and this condensation causes heat to be generated over the sensing junctions. For a sensor that is operating at standard temperature and pressure (“STP”), the analytes that condense are liquids at STP. Typical breath constituents include: carbon dioxide, oxygen, nitrogen, and water. Apart from water, none of these compounds normally will condense onto a surface under these conditions.
Candidate analyte interactants that may be useful in presently preferred embodiments and method implementations according to various aspects of the invention include organometallic vapochromic materials, such as [Au2Ag2(C6F5)4(phen)2]n. These types of materials are powders at room temperature, which make them easy to deposit, and react with volatile organic compounds, such as acetone, in the gas-phase. These materials are designed to change color upon exposure to a particular analyte, which color-change causes a change in thermal energy.
The interactant may also be regenerative. Examples of regenerative interactants may include interactants that are true catalysts. Or, regenerative interactants may be interactants that can be regenerated (after they are consumed or partially consumed) by use of a refilling gas stream. For instance, particularly for living or polymeric interactants, interactants may become more reactive when exposed to water. In such instances, water may be used to regenerate the immobilized analyte interactant after it has been consumed or partially consumed by exposure to the analyte. Referring once more to polymeric interactants, while analyte interactants may be or comprise polymers, they are not limited to them.
The interactant may be immobilized on the sensing junctions directly. If, however, the interactant can cause corrosion or other negative impacts to the thermopile materials which will affect the longevity of the device, other embodiments may be better suited. Preferably, the interactant is immobilized on the side of the substrate opposite the thermopile in such a way that the heat will be transferred preferentially to the sensing junctions. In thin isotropic materials, this is achieved by immobilizing the chemical directly over the sensing junctions.
Optionally, and advantageously, the substrate can be folded so as to allow for creation of a catheter-type device.
The thermopile device configurations shown in FIGS. 1 and 2 are merely illustrative and are not necessarily limiting. FIG. 3, for example, shows a schematic showing a circular thermopile. Thermopile conductors will be deposited onto a substrate 15 on which a first conductor material 16 and a second conductor material 17 are deposited to form reference junctions 18 and sensing junctions 19. The interactant 20 would be deposited proximate to the sensing junctions 19. The voltage can be measured by use of the contact pads 21.
Laboratory prototype thermopiles were constructed with the geometry illustrated in FIG. 2. Bismuth metal was first evaporated onto a polyimide Kapton® thin film substrate through a mask. Once the bismuth deposition was complete, the substrate-mask combination was removed from the metal evaporator. The bismuth mask was removed and an antimony mask clamped to the substrate in such a manner that the antimony deposition would complement the bismuth deposition layer to form the thermopile. Once the antimony deposition was complete, a thin layer of bismuth was deposited on top of the antimony. It has been determined empirically that the thermopile yield is improved significantly. Nevertheless, it must be noted that certain commercially available thermopiles demonstrate less background noise than the prototypes described herein.
To make electrical contact to the thermopile contact pads 12, thin copper wire was attached through the use of a silver bearing epoxy paint.
FIG. 4 shows a side cross-section of a thermopile sensor as it was installed in a housing. Illustrated are sensing junctions 22, reference junctions 23, and thermopile conductor legs 24 connecting the junctions deposited on deposited on a substrate 25 as described above. For the prototypes, the substrate was placed on a plastic annulus 26 approximately 25 mm in diameter with the metals facing inside the annulus into cylindrical region 27 and the substrate 25 facing the external environment. The cylindrical region 27 was filled with polyurethane insulation. On the other side of the substrate, silicone grease 28 (not shown to scale) was placed such that it covers the area over the entire thermopile. An interactant 29 was placed over the sensing junctions 22 of the thermopile. The copper wires (not shown) protruded from beneath the substrate 25. The advantage of this approach is that the metal of the thermopile are not exposed to the external environment, but the thermal path to the interactant 29 is longer.
FIG. 5 illustrates the top view of the sensor illustrated in FIG. 4, showing the substrate 25 placed on a plastic annulus 26 with the metals facing the inner cylinder of the annulus. Copper wires 30 are electrically connected to the contact pads of the thermopile. The silicone grease 28 is placed over the entire thermopile and the reactant 29 is placed only over the sensing junctions.
For this type of sensor, the ideal chemical reactant is regenerative (not consumed), highly selective to the analyte of interest, and non-toxic, has a long shelf life, and engages in a highly exothermic or endothermic reaction with the analyte or analytes.
This setup has been tested with sodium hypochlorite, hypochlorous acid, and trichloroisocyanuric acid. In this case, the chemical reactants are not in direct contact with the thermopile metals 14. Rather, the chemicals are immobilized on the substrate 13 opposite the thermopile metals 14. The disadvantage of this configuration is that heat must be transferred through the substrate. However, the substrate is extremely thin and therefore the resistance to heat transfer is low. The advantage is that there is no effect of the interactant on the thermopile and also the interactant can be removed and replaced without impact to the thermopile.
Referring also to FIG. 2, the area of the substrate 13 surface that was vertically above the entire surface of the thermopile was coated with silicone vacuum grease to keep the thermal load on both the reference and sensing junctions approximately constant thereby allowing the time constant of the two sets of junctions to be equal. Initially, double-stick cellulose acetate tape was utilized instead of the silicone grease. However, it was determined empirically that acetone reacts with the adhesive portion of the tape, thereby causing a series of competing reactions. A precise volume of trichloroisocyanuric acid was dusted onto the silicone grease over only the portion of the substrate 13 which was vertically above the sensing junctions 10 in precise geometrical fashion by use of a rectangular mask.
Once a thermopile unit is created with the chemical immobilized and wires attached, it should be housed in a device that will allow for an interface with the breath or analyte of interest. In this embodiment, a laminar flow chamber was constructed (generally illustrated in FIG. 23). To decrease the chances of turbulent flow, sharp edges were removed from the system. A rectangular conduit was selected with a top and bottom piece. The height was made extremely small, again to minimize the chances of turbulent flow.
Two circular holes 161 and 162 of different diameters were drilled in the top plate of this conduit 160 through the top. One hole allowed the gas with the analyte to enter the chamber. The second hole tightly fit the thermopile sensing unit with the chemicals facing downward and into the slit. It is believed that this allowed air with the desired analyte to enter the flow chamber through the small hole, achieve fully developed laminar flow through the course of the conduit and interact with the chemical on the downward facing thermopile.
FIG. 6 shows the results of a test with acetone in air reacting with a trichloroisocyanuric acid reactant. Curves 31, 32, 33, and 34 show the output voltage (in microvolts) as a function of time (in seconds) for an acetone concentration of 455, 325, 145, and 65 ppm respectively.
FIG. 7 shows the result of the same apparatus as a function of acetone concentration in ppm. Pulses of acetone of various concentrations were admitted to the conduit and the signal measured. The aspect of the raw data shown as the signal in FIG. 7 is the peak voltage output measured by the sensor. As may be seen, there is a very strong correlation between signal voltage and concentration. Thus, making a calibrated system should be quite practical.
FIG. 8 shows theoretical curves generated by a mathematical model for the same sensor and analyte concentrations as show in FIG. 6. Similarly, curves 35, 36, 37, and 38 show the output voltage (in microvolts) as function of time for an acetone concentration of 455, 325, 145, and 65 ppm respectively.
This example discusses the sensor setup for the case when the analyte is brought into contact with the thermopile sensor principally via diffusion. In other words, the thermopile sensing unit would operate in a stagnant or low flow environment.
A large glass Petri dish was used to simulate this system. The thermopile was mounted as described herein above. This unit was adhered centrally to the base of the Petri dish. The electrical leads from the thermopile were vertically suspended. The top of the Petri dish was covered rigorously with two pieces of Parafilm®, allowing the leads to exit the dish. (Parafilm® is a flexible film commonly used for sealing or protecting items such as flasks, trays, etc. and is a product of the American Can Company.) This setup was immobilized.
Instead of introducing acetone by creating flow over the thermopile, liquid acetone was injected into the Petri dish. Thus, acetone was allowed to evaporate into the ambient above the dish. Once acetone molecules were in the vapor phase, they diffuse to the surface of the thermopile and begin to interact. This setup was tested with hypochlorous acid, sodium hypochlorite, trichloroisocyanuric acid, and sodium dichloroisocyanurate dihydrate.
FIG. 9 shows the experimental results generated by this embodiment. As shown, curve 40 has half the acetone concentration as curve 39. The acetone concentrations may be high for physiological applications. However, the significance is that the sensor is capable of measuring analytes that are transferred to the sensor by diffusion only. While it may appear that the process is slow due to the peak at 50 seconds, it is advantageous to note that the analyte, in this case acetone, was injected in liquid form and had to evaporate and then diffuse to the surface of the device prior to any possible reaction.
FIG. 10 shows a possible embodiment for use in a hospital environment using a patient gas mask. Expired air 41 is generated either from the oral or nasal cavities. The breath is captured by a face mask 42 (which may be of standard gas mask design or some other) and is then directed through a polyethylene tube 43 where it is then filtered by a particle filter 44. The breath is directed by the tubing to a distendable volume 45 that is well-stirred by fan or other method 46. The flow of the breath through a channel 47 that leads to a chamber 48 containing the sensor can be controlled by a valve 49 that leads to the ambient environment.
The distendable volume 45 would allow for well-mixed fluid to enter the channel 47 in a regulated, laminar flow manner. As a result, variations in patient breath such as flow velocity patterns, interfering substances, temperature gradients, and particulate matter would be controlled, normalized, and mixed prior to introduction to the sensor inside chamber 48. This is useful, for instance, because the first volume of expired air is non-physiologically active (i.e. lung dead space).
The filter 44 is used because it may also be desirable to filter the breath before it enters volume 45. Different types of filters may be employed. First, a particle filter can be used. There are, of course, varying levels of particle size, shape, and type that can be considered. A simple particle filter, primarily to remove food residue, should suffice. Second, there are many filters which remove moisture from the breath. For instance, the entering breath can be directed to a channel wherein a water absorbent such as silica gel is immobilized and which will absorb all of the water. As may be appreciated, this may or may not be desirable depending on whether water is employed for the chemical reaction.
In this environment, the sensor could be used for continuous monitoring of patients. Suitable, well known, electronics could be used to communicate with nurses' stations, hospital computers or set of local alarms.
A very advantageous analyte is ammonia. Breath ammonia is found in elevated concentration in patients with renal or liver failure. If ammonia were the analyte in the gas, ammonia can react with many different substances. As an example, ammonia reacts with hydrochloric acid to form ammonium chloride. The ammonium chloride will subsequently react with barium hydroxide to form barium chloride, ammonia, and water. This will allow for a two-step reaction sequence thereby increasing the total enthalpy of the reaction producing an amplification of the enthalpy.
It is advantageous to note that this device can be used to measure the concentration of multiple analytes simultaneously. Thus, by use of multiple thermopiles, an entire screening can be performed with one breath.
FIG. 11 shows a first possible chemical immobilization technique for chemical amplification. The gas containing the analyte 50 enters the conduit 57. Some of the gas exits at the end of the conduit. However, some of the gas passes through the pores 52 of the channel wall 53. Next to the channel wall, one interactant 54 is located and then a second interactant 55. This gas leaves the conduit through the outer semi-permeable conduit walls 56. Referring to FIG. 13, the thermopile consists of reference junctions 61 and sensing junctions 59 and 60. The sensing junctions can be single or multiple sets, depending upon the physical size of the junctions.
FIG. 12 shows a second possible method of immobilizing the chemical. In this case, the wall 56 is impermeable and all gases flow through the conduits.
Reference will now be made to FIGS. 14 and 15. In operation, the fluid 75 enters the conduit through a mouthpiece. The fluid flow 75 is then divided between two tubes 76 both of which direct the fluid 75 into the reaction chamber, which is insulated. The fluid 75 first passes across a set of reference junctions 70. Then, the fluid 75 changes direction and begins to pass over the first set of sensing junctions 71 of the thermopile. The sensing junctions 71 are each coated with interactant 74. However, the sensing junctions 71 are separated from one another by the legs of the thermocouple, with further sensing junctions 71 in a subsequent channel. Therefore, the fluid 75 passes over a section of interactant 74 and then a section where interactant 74 is absent. Once again, the fluid 75 changes direction and passes over a second set of sensing junctions 71, which are distributed in the same way as described earlier. Finally, the fluid 75 exits the chamber at the opening 77 at the back-end.
FIG. 15 shows a cross section having the structure of FIG. 14. Interactant 74 is deposited on thin film substrate 69 on which is deposited sensor thermopile material 78. The device is surrounded by a thermal insulating structure 79. Fluid flow 73 carries the analyte past the interactants 74. As analyte is taken up by the interactant, its concentration drops in the layers next to the top and bottom. Diffusion from the center acts to replenish the depletion, but, depending on the reaction kinetics, chemistry mechanisms, flow regime, etc. this may not be enough to compensate. After passing the interactants 74, the concentration next to the top and bottom is not depleted, but is replenished by diffusion from the mid part of the flow. Based on theoretical considerations and considerations such as those described herein, the rate of uptake at a subsequent downstream interactant will be higher than if there were no replenishment zone. Thus, the uptake process is more efficient. Less total interactant in the device can be used for the same overall uptake of analyte.
The dimensions for this embodiment are provided. These dimensions, however, are merely illustrative of this particular embodiment. The mouthpiece should have dimensions of approximately 0.0212 m, the reaction chamber will be a conduit with a square-shaped cross-section of dimensions 0.0762×0.0762 m2. Each channel is 0.0106 m wide and the channel barriers are 0.00254 m each. There are six channels and five channel barriers. The chemical (analyte interactant) is immobilized for lengths of 0.001 m with gaps between chemical of 0.001 m distance. The chemical is immobilized with appropriate particle size to engage in a reaction with a thickness of about 0.001 m. The channel height is 0.0206 m. The thickness of the thermopile metals can vary, but as in the previous examples, the metals are approximately 3 μm thick and the Kapton substrate is approximately 50 μm.
Compared with the chemistry and analyte of the working prototype with illustrative output as shown in FIG. 6, this device is expected to increase the signal generated by a factor of approximately 100 times at least.
Use of channel separators over the thermopile itself may be useful in nanotechnology or microfluidics applications. Certain embodiments lend themselves well to miniaturizing the device by miniaturizing the sensor. In other embodiments, however, it may be desirable to miniaturize the channels through which the analyte flows but maintain the sensor in a current physical size. FIG. 14 shows one embodiment that employs channel separators 72.
As illustrated, the replenishment zone relies on diffusion from the bulk stream. However, the replenishment of the outer layers could be augmented by providing mixing. This happens to some extend as the fluid makes a turn in the serpentine path in FIG. 14. Also, obstructions could be placed in the center of the conduit after each interaction zone. They could, for example, be round wires stretched across the center of the conduit. Small flat plates may create more turbulence and better mixing.
In addition to passive measure, one could use mechanical agitation. This could be provided with piezoelectric elements or by shaking the entire device.
The surface concentration of the analyte is generally limited by the input concentration of analyte (while this is generally true, there may be instances where this may not be the case). Thus the surface concentration of analyte can vary from zero to the input concentration. The flux to the surface, however, tends to decrease as a function of distance along the surface unless the interaction region is interrupted. Theoretically, if the interaction regions are made vanishingly small and large in number, such an embodiment uses the least amount or interactant for any given signal. Normally, it is not necessary to react all of the analyte, just enough to get a strong signal.
This use of one or more replenish zone between interactant zones (a.k.a. interrupters to the concentration boundary layer) has quite general utility. Dilute solutions of almost all analytes in almost all fluids and/or gases will diffuse based on a concentration gradient. As such, embodiments and methods involving the replenish zone can be applied to fluids broadly, which includes not only gases but liquids as well. For example, a thermopile coated with an interactant (e.g. an enzyme) that is patterned using the replenish zone may operate in the blood stream, cell culture media, or water treatment plants.
Furthermore, the use of one or more replenish zones between interactant zones may be applied broadly to embodiments which employ different sensors and/or sensing methods. Most sensors operate based on the interaction of the analyte with an analyte interactant. As discussed herein, the amount of “reaction” that takes place may be enhanced by certain modes of patterning the interactant, such as the use of a replenishment zone. Thus, any sensor or combination of sensors that quantify the amount of analyte present in a fluid (e.g. liquid, gas, etc) may benefit from the use of a replenishment zone. For example, if the reaction between the one or more analyte and with the one or more analyte interactants produces heat, then a thermal sensor such as a thermopile, pyroelectric device, or a thermistor may be well suited for the application. However, the use of a replenish zone is not limited to heat measurement. Other outputs of reactions that produce a reaction that can be sensed would benefit from this design. For instance, if the reaction produces electromagnetic radiation (e.g., light, infrared radiation), a remote sensor (e.g. a camera, IR detector, etc) could be used.
Referring now to FIG. 37, the sensors 261 and 262 that employ replenish zones or use the concentration boundary layer interruption methods are not limited to thermopiles or thermocouples. Examples of sensors comprise one or more of the following: thermistor, thermocouple, pyroelectric, thermopile, ion sensor, radiation sensor, electrochemical sensor, piezoelectric sensor, optical sensor, etc. Sensor 261 may be or comprise an electrochemical sensor. Sensor 262 may be or comprise a thermopile in one application and a piezoelectric sensor in a different application. In this manner, the specificity and sensitivity of the overall device may be improved.
There are other ways by which the specificity and/or sensitivity of thermal sensors can be enhanced. One approach is to increase the amount of heat that is produced either for a particular binding event or at any point in time.
Most pyroelectric materials are also piezoelectric in nature. Therefore, it is possible to combine these two methods of detection into one sensing unit. This may enhance the specificity/selectivity of the sensor. This is particularly relevant if the analyte is a biological material (e.g., glycoproteins, cell receptors, etc) that is being detected from a body fluid (e.g. blood, spinal fluid, synovial fluid, urine, etc). For instance, if one is attempting to detect glycoproteins via the sugar moiety, it may be necessary to discriminate between sugar moieties that are actually bound to the protein versus free flowing sugar moieties. In this instance, a mass transducer, such as a piezoelectric sensor, may be used to discriminate based on the mass of the binding agent. This is exemplified in FIG. 50 where 390 is a glycoprotein and 391 is a free flowing sugar moiety.
Another way to increase the specificity of the thermal sensor is by using a multiple-binding event. Basically, the analyte is confirmed if two binding events take place. These binding events could be detected by two different sensors (e.g., both or nothing) or by the same sensor (e.g. increased heat). The use of the second binding site may be helpful in discriminating between same-species interfering substances.
FIG. 51 shows an embodiment in which at least two thermal sensors (400 and 401) are used. In this embodiment, there are two analyte interactants (402 and 404). Two analytes are shown in the figure. The first analyte has the two binding sites (405 and 406) necessary for interaction with the two analyte interactants (402 and 404). The second analyte has only one 403 of the binding sites. In this embodiment, the sensors 401 and 402 can discriminate between the first analyte and the second analyte, which may be advantageous if one of them is an interfering substance.
FIG. 52 shows an embodiment in which two binding sites are used to discriminate between different chemicals/molecules (the second binding site is designated by a dashed line). The analyte interactant has two different interactant binding sites (410 and 411). The analyte may be or comprise a molecule with different functional groups or analyte binding sites. One of the analyte binding sites 412 binds with the interactant binding site 410. The second analyte binding site 413 binds with the second interactant binding site 411. A potential interfering substance also has two binding sites 414 and 415. While one of the interfering substance's binding sites 414 does bind to one of the interactant binding sites 412, the second of the interfering substance's binding sites 415 does not bind to the second interactant binding site 411.
An embodiment that aids in increasing sensitivity is shown in FIG. 53. In this embodiment, a “concentrator” is used. This concentrator 420 is designed to capture all of the analyte (e.g. activated carbon may be used to capture volatile organic compounds). Once the analyte is captured, it is “flushed out” from the concentrator via some mechanism such as a heater 421. In this way, the concentration of analyte in the “flushed” fluid is greater.
Chemical reactions in the liquid phase are generally better studied than those in the vapor phase. In aqueous solutions, hydrogen and hydroxide ions are often involved in acid or base-catalyzed reactions. One possible embodiment of the invention shown in FIG. 16 provides an apparatus and method by which the analyte in the gas may be condensed to liquid form.
The sensor shown in FIG. 16 is designed to condense a gas to a liquid. In this embodiment, in medical applications, the breath would condense prior to exposure to the sensor. This embodiment takes advantage of the improved diffusivity of analytes in a gas as compared to in a liquid. Simultaneously, the heat loss in a liquid is far less than in a gas under similar physical conditions. This design also allows one to take advantage of the well-researched liquid-phase acetone reactions.
One of the problems that frequently arises with chemical sensors is chemical depletion. In other words, the chemical reactant is consumed over a period of time. One way to circumvent this problem is to use chemistries that have a long lifetime and/or are not consumed in the reaction (enzymes or catalysts). However, even if an enzyme is used instead of an inorganic chemical, enzyme deactivation or degradation remains a problem. Here two embodiments of the present invention are presented which specifically address the aforementioned problem.
In one embodiment, the sensor is made “removable” from the overall breath collection chamber. This is done by fashioning the sensor as a probe or by fashioning the substrate such that it takes on a three-dimensional shape, for instance, of a catheter. FIG. 17 shows the thermopile where the sensing junctions are positioned in one area 120 and the reference junctions in another area 121. The substrate 122 is folded to form a cylindrical tube. If the substrate on which the thermopile is deposited is flexible, then the thermopile itself can be formed around, for example, a cylindrical insulator. In this way, the thermopile can be made into a catheter-style device.
In another embodiment, a thin absorbent material exposed to some interactant, for example hypochlorous acid, is wrapped around the sensing junctions of the thermopile. Optionally, the reference junctions may be wrapped with a non-exposed absorbent material. FIG. 18 shows a possible method by which chemical can be immobilized on the thermopile in, for example, the embodiment described in FIG. 17. A material 126 is exposed to a chemical interactant 127 and the interactant-coated threading material 123 is wrapped around the sensing junctions 120 and the reference junctions are either coated with unexposed material 126 or left uncoated. In another embodiment, the entire thermopile with material is placed in a chamber 125 wherein the analyte interacts with it.
Thermal sensors according to these aspects of the invention and as generally described herein can be designed, configured and used to measure the concentration of multiple analytes, preferably simultaneously. Thus, for example, by use of multiple thermopiles or pyroelectric sensors, an entire screening can be performed with one breath.
More than one interaction can also occur simultaneously or sequentially. This can occur if multiple interactants are immobilized on the sensing portion of the device. Alternatively, the product or intermediary, etc. of a first reaction may initiate a set of secondary reactions, which may or may not involve the analyte. In any case, the net enthalpy of these interactions dictates the response of the device. A non-zero net enthalpy causes a temperature change on the sensing junctions relative to the reference junctions, which temperature change can be quantified by measuring the output voltage.
Even if only one interaction occurs, the chemistry may be selected such that the products of the initial reaction act as reactants during secondary interactions with the analyte or other substances which can amplify temperature changes.
In other cases, measuring multiple analytes may be desirable. In the presently preferred embodiments, each thermopile within the array may be coated with a different material such that selectivity of several analytes is determined by the different interactions. The response of the individual thermopiles is determined by the individual thermopile voltage response which creates an overall profile. This profile or pattern will be characteristic of a specific analyte or analytes of similar chemical family and can therefore be used to identify at least one analyte. This can be adapted to pyroelectric sensors as well.
Thus, a single analyte interactant may be used to sense one or more analytes. This may be useful when a single analyte interactant senses a class of analytes. Or, multiple analyte interactants can be used to sense a single analyte very specifically. Or, multiple analyte interactants can be used to sense multiple analytes (e.g., for screening purposes).
If multiple devices are used either to more selectively identify the analyte or to reduce the error of a single device, then there are some geometry considerations that may be advantageous. For instance, the devices could all be placed side by side as close to the leading edge as possible. FIG. 22 shows a possible embodiment of a device 152 containing multiple sensors 153 where the sensors are placed side by side close to the leading edge of the device. If this is not possible or desirable under the circumstances, then the devices could be placed with gaps between them. The exact geometry can vary from one setup to the next. One may place the devices in a chess-board like pattern because the formation of the boundary layer is streamline-specific. FIG. 21 shows another setup of a device 150 where multiple sensors 151 are placed in a chess-board like fashion.
For most applications, it is desirable to minimize the time required to determine the concentration of the analyte. In some instances, this is motivated because the analyte of interest is of critical importance to patient care. In other instances, for example in breath analysis, the user can only breathe into the device for a finite period of time.
Additionally, under most circumstances, the analyte in the gas stream is the limiting reagent in the chemical reaction or enthalpic process. Therefore, given the limited availability of the analyte (both in terms of time and concentration), it is often desirable to maximize the amount of analyte that is involved in the enthalpic process and therefore available to generate or consume heat.
To maximize the surface analyte concentration, various parameters of the system must be optimized. The following provides a method for doing this.
First, one defines the physical setup and environment in which the sensor might be working. Typical considerations include the geometry (e.g., flat plate, rectangular slit, conduit), nature of the flow environment (e.g., highly controlled or unpredictable), and physical properties (e.g., diffusivity, heat transfer coefficient, reaction enthalpies).
Second, the surface flux of the analyte is determined. The chemical kinetics, flow regime, and various physical properties preferably are considered for this analysis. The nature of the flow is particularly advantageous and can vary depending on the sensor design and geometry layout (e.g., straight or coiled flow path). Depending on the geometry, the entire length of the sensor may be exposed to the analyte during the time period designated for analysis. In other instances, however, such as pulsatile flow, certain parts of the sensor may be exposed to a bolus of fluid, which would create a time-varying flux.
Third, the surface analyte flux is maximized by selecting or optimizing parameters of the system. As with any optimization exercise, engineering tradeoffs must be made. For example, we may optimize the chemical patterning and balance the sensor placement with the conduit height.
This method can be employed in a wide variety of applications. A particular example is presented below to illustrate.
Step 1: Define Physical Setup and Environment in which the Sensor is Working
In this embodiment, the sensor is part of a rectangular hand-held acetone-measuring device that is intended for consumer use. The geometry of the device is generally described by FIG. 14. Because it is a hand-held device, the length and width are specified as 3′′ in dimension. There will be 5 channel separators and 6 channels, as shown in FIG. 14. The flow rate is likely to be variable with time and therefore the implications can be accounted for. It is desirable to maximize the flux of acetone to the surface of the thermopile sensor where acetone engages in an assumed instantaneous reaction with an immobilized chemical.
The following dimensions are arbitrarily chosen (here, the term “arbitrary” indicates that the dimensions are not defined by mathematical computations, but rather by other factors such as human factors engineering, compatibility with standard connection pieces, etc). The mouthpiece has a diameter of approximately 0.0212 m, the reaction chamber will be a conduit with a square-shaped cross-section of dimensions 0.0762×0.0762 m2. There are six channels and five channel barriers. Each channel is 0.0106 m wide and the channel barriers are 0.00254 m each. The thickness of the thermopile metals can vary, but as in the previous examples, the metals are approximately 3 μm thick and the Kapton substrate is approximately 50 μm.
Because acetone levels of physiological importance are extremely low concentrations, the physical properties of the acetone-air mixture are assumed to be equal to those of air and are further assumed constant: the kinematic viscosity, v, is v=1.69·10−5 m2/s, and the diffusivity of acetone in air, D, is D=8.5·10−6 m2/s, and the Prandtl number, Pr, is Pr=0.7.
To fully define the device according to FIG. 14, the following parameters can be determined: (1) length of chemical deposit and length of gap between chemical deposits and (2) conduit height. In order to adequately select these parameters, one determines the flux of acetone to the surface.
Step 2: Determine the Flux of Acetone to the Surface
Assuming incompressible flow, constant physical properties, and negligible body forces, the concentration boundary layer thickness, δC, is given by the following relationship:




  
    δ
    C
  
  =
  
    δ
    
      Sc
      
        1
        /
        3
      
    
  




where δ is the thickness of the hydrodynamic (velocity) boundary layer and Sc is the dimensionless Schmidt number that is used to create momentum and mass transfer analogies. The Schmidt number is given by:





  Sc
  =
  
    v
    D
  




where v is the kinematic viscosity and D is the diffusivity. The thickness of the hydrodynamic boundary layer is given by:





  δ
  =
  
    
      5
      ⁢
      x
    
    
      
        Re
      
      x
    
  




where x is the distance from the entrance of the conduit and Re is the dimensionless Reynolds number which, given the rectangular slit geometry, is given by:





  
    Re
    x
  
  =
  
    
      u
      ·
      x
    
    v
  




where u is the velocity of the gas and v is the kinematic viscosity. The velocity is, of course, equal to the flow rate divided by the cross-sectional area.





  u
  =
  
    Q
    
      W
      ·
      h
    
  




where Q is the flow rate of the gas stream, W is the width, and h is the height. Therefore, by combining the above equations, the thickness of the concentration boundary layer is given by:





  
    δ
    C
  
  =
  
    
      
        5
        ⁢
        x
      
      
        
          Re
          
            1
            /
            2
          
        
        ⁢
        
          Sc
          
            1
            /
            3
          
        
      
    
    =
    
      5
      ·
      
        v
        
          1
          /
          6
        
      
      ·
      
        D
        
          1
          /
          3
        
      
      ·
      
        Q
        
          
            -
            1
          
          /
          2
        
      
      ·
      
        
          (
          
            x
            ·
            W
            ·
            h
          
          )
        
        
          1
          /
          2
        
      
    
  




The units of the thickness are in meters. Assuming that mass transfer in the direction of flow is dominated by convection (and not diffusion) and assuming that the flow is uniform with respect to the width of the conduit, the diffusion is directed only unidirectional, from the bulk stream to the surface. The flux of molecules to the surface is given by Fick's Law:




  N
  =
  
    
      -
      D
    
    ⁢
    
      
        
          d
          C
        
        
          d
          y
        
      
      ~
      D
    
    ⁢
    
      
    
    ⁢
    
      
        
          Δ
          ⁢
          
            
          
          ⁢
          C
        
        
          Δ
          ⁢
          
            
          
          ⁢
          y
        
      
      ~
      D
    
    ⁢
    
      
    
    ⁢
    
      
        
          C
          bulk
        
        -
        
          C
          surface
        
      
      
        
          δ
          C
        
        -
        0
      
    
  




where Cbulk is the concentration of acetone in the bulk stream (mol/m3). Assuming an instantaneous surface reaction, the concentration of analyte at the surface would be approximately equal to 0. Under this theoretical set of conditions, the above equation reduces to:





  
    N
    ~
    D
  
  ⁢
  
    
  
  ⁢
  
    
      C
      bulk
    
    
      δ
      C
    
  




the above equation can be modified to consider more complicated chemical kinetics and/or other conditions to determine the flux of analyte to the surface. Applying the relationship for the concentration boundary layer as computed above, the surface flux of analyte is given by:





  
    N
    ~
    
      1
      5
    
  
  ·
  
    
      D
      
        2
        /
        3
      
    
    
      v
      
        1
        /
        6
      
    
  
  ·
  
    
      
        C
        bulk
      
      ·
      
        Q
        
          1
          /
          2
        
      
    
    
      
        (
        
          x
          ·
          W
          ·
          h
        
        )
      
      
        1
        /
        2
      
    
  




Thus, the flux to the surface is directly proportional to the concentration and the square root of the flow rate. The flux is also inversely proportional to the distance from the leading edge.
We want to maximize N. From this equation we conclude that the surface flux is driven by geometric and flow parameters. It is advantageous to note that the above methodology can be adapted to encompass more complicated scenarios including chemical kinetics, which would necessitate, for example, the incorporation of kinetic coefficients in the solution.
Step 3: Determining Parameter Values
Another consideration is the length of chemical deposition. In other words, if the chemical is immobilized in a discontinuous fashion, what is the ideal immobilization length?
If the chemical is distributed in a discontinuous fashion as described earlier in this specification, the amount of analyte that will be involved in the reaction increases tremendously. The surface flux of acetone is given below as:




  
    N
    ~
    
      1
      5
    
  
  ·
  
    
      D
      
        2
        /
        3
      
    
    
      v
      
        1
        /
        6
      
    
  
  ·
  
    
      
        C
        bulk
      
      ·
      
        Q
        
          1
          /
          2
        
      
    
    
      
        (
        
          x
          ·
          W
          ·
          h
        
        )
      
      
        1
        /
        2
      
    
  




While the chemical deposition on the conduit surface is continuous, the flux of analyte to the surface decreases as a function of distance from the leading edge. The maximum flux to the surface occurs at a point extremely close to the leading edge. However, as has been described in detail previously, if the growth of the concentration boundary layer is interrupted by a lack of chemical reagent or some type of flow interruption, the boundary layer will reform and a new leading edge will be created. Nevertheless, during this “interruption,” there will be no flux to the surface and no reaction (and therefore no heat). Therefore, we must balance the diminished flux due to build-up of the boundary layer with the high and then lack of flux with the chemical patterning.
Accordingly, the question is: what is the ideal chemical deposit length and gap between deposits? The cumulative flux of acetone between the leading edge, x=0, and some distance, x=x2, is given by:




  
    
  
  ⁢
  
    
      N
      cum
    
    =
    
      
        ∫
        
          N
          ⁢
          
            d
            x
          
        
      
      =
      
        
          
            1
            5
          
          ·
          
            
              D
              
                2
                /
                3
              
            
            
              v
              
                1
                /
                6
              
            
          
          ·
          
            
              
                C
                bulk
              
              ·
              
                Q
                
                  1
                  /
                  2
                
              
            
            
              
                (
                
                  W
                  ·
                  h
                
                )
              
              
                1
                /
                2
              
            
          
          ·
          
            
              ∫
              
                x
                =
                0.001
              
              
                x
                =
                
                  x
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
            ⁢
            
              
                1
                
                  x
                  
                    1
                    /
                    2
                  
                
              
              ⁢
              
                d
                x
              
            
          
        
        =
        
          K
          ·
          
            x
            2
            
              1
              /
              2
            
          
        
      
    
  




where K is a lumped constant consisting of the other parameters, which, for this aspect of the problem are assumed to be constant. Assuming K to be K=1 for the sake of simplicity, FIG. 29 shows the nature of the relationship between the cumulative flux and distance from the leading edge. Therefore, the rate of increase of the cumulative flux decreases as the distance from the leading edge increases. For an interrupted pattern to be effective, the cumulative flux over a distance must be more than half of the cumulative flux over four times that distance. Written mathematically,





  
    
      N
      cum
    
    ⁡
    
      (
      
        x
        ideal
      
      )
    
  
  >
  
    
      1
      2
    
    ·
    
      
        N
        cum
      
      ⁡
      
        (
        
          4
          ·
          
            x
            ideal
          
        
        )
      
    
  




Using the above relationship, if, for example, xideal=0.01, there will be two distances between 0<x<0.02 m and 0.04<x<0.06 m where chemical will be patterned. During 0.02<x<0.04 m, the chemical boundary layer will be depleted. With this patterned method, the cumulative flux over the entire 0.0762 m length will be:




  
    N
    cum
  
  =
  
    
      0.381
      ⁢
      
        mol
        
          m
          ·
          s
        
      
      ⁢
      
        
      
      ⁢
      versus
      ⁢
      
        
      
      ⁢
      
        N
        cum
      
    
    =
    
      0.276
      ⁢
      
        mol
        
          m
          ·
          s
        
      
    
  




if the entire 0.0762 m length were coated with chemical. This is 38% more efficient.

However, if xideal=0.005, the cumulative flux over the entire 0.0762 m length will be:




  
    N
    cum
  
  =
  
    
      0.539
      ⁢
      
        mol
        
          m
          ·
          s
        
      
      ⁢
      
        
      
      ⁢
      versus
      ⁢
      
        
      
      ⁢
      
        N
        cum
      
    
    =
    
      0.276
      ⁢
      
        mol
        
          m
          ·
          s
        
      
    
  




if the entire 0.0762 m length were coated with chemical. This is almost 95% more efficient. This can be seen in Table 2, below.













TABLE 2







RANGE (M)

CHEMICAL
FLUX





















0
0.005
Yes
0.07



0.005
0.01
No
0



0.01
0.015
Yes
0.07



0.015
0.02
No
0



0.02
0.025
Yes
0.07



0.025
0.03
No
0



0.03
0.035
Yes
0.07



0.035
0.04
No
0



0.04
0.045
Yes
0.07



0.045
0.05
No
0



0.05
0.055
Yes
0.07



0.055
0.06
No
0



0.06
0.065
Yes
0.07



0.065
0.07
No
0



0.07
0.075
Yes
0.07



0.075
0.08
No
0





TOTAL
0.56










Practically, it may be difficult to pattern the chemical in this discontinuous fashion, depending on the application. However, clearly, if it is possible, it is advantageous to do so as there is twice as much analyte diffusing to the surface with 50% of the reacting chemical immobilized on the sensor.
To operate in an environment where the flux is maximized and therefore possibly prior to the fully-developed flow regime, the hydrodynamic boundary layer thickness must be less than half of the conduit height. Therefore, the concentration boundary layer is confined by the height:




  δ
  =
  
    
      
        
          5
          ⁢
          x
        
        
          
            Re
          
          x
        
      
      ⁢
      
        5
        ·
        
          v
          
            1
            /
            2
          
        
        ·
        
          x
          
            1
            /
            2
          
        
        ·
        
          
            (
            
              
                W
                ·
                h
              
              Q
            
            )
          
          
            1
            /
            2
          
        
      
    
    <
    
      h
      2
    
  




The maximum length, x, is 0.0762 m. The conduit width, W, as previously stated is W=0.0106 m. Therefore, this inequality can be shown in FIG. 30. The entry length, Le, is the length required before the flow is fully developed, which means that the velocity profile does not change from one point to the next along the length of the conduit. To be in the non-fully developed region and assuming a rectangular slit geometry, the thermopile would be placed within the entrance length, which would be:




  Le
  ≈
  
    0.04
    ·
    h
    ·
    
      Re
      D
    
  
  ≈
  
    
      0.08
      v
    
    ·
    Q
    ·
    
      h
      
        W
        +
        h
      
    
  
  >
  
    0.0762
    ⁢
    
      
    
    ⁢
    m
  




Note that





  
    Re
    D
  
  =
  
    
      u
      ·
      
        D
        h
      
    
    v
  




where Dh is the hydraulic diameter.

The entry length must be at least 3′′, which was stated in the problem statement as the maximum length of the device. FIG. 31 is a graph of this inequality. Since heights need not assume negative values, a flow rate greater than approximately 1 LPM is employed to ascertain that the entry length is not achieved within the 0.0762 m (3′′) length of the device.
Combining the above two constraints, we obtain the relationship shown in FIG. 32, where the shaded region is the solution to the set of two inequalities.
Looking at the equation of the analyte flux to the surface, as the height of the conduit increases, the flux decreases. Therefore, the height should be kept at the smallest possible value, while still conforming to the above constraints shown graphically in FIG. 32.
Turning to another method according to the invention, while the preferred embodiments may be used in highly controlled environments, it is also possible that the device be used in situations where user variability is a concern. One variable that one may account for is the flow rate of the user.
As we have seen in the previous model, as the flow rate increases, the analyte flux to the surface increases. However, as the flow rate increases, the amount of heat that is dissipated to the environment also increases. Therefore, as the flow rate increases, it is desirable to balance the increase in heat generated with the increase in heat dissipated.
This model serves to investigate the impact of flow rate on the signal and attempts to identify particular signal features that may be independent of flow rate.
Assuming that the thicknesses of the chemical on the thermopile and the thermopile substrate are low and/or that their thermal conductivity is high, the temperature at the surface of the chemical is equal to the temperature of the thermopile. With this assumption, an energy balance of the thermopile yields:




  
    ρ
    ⁢
    
      
    
    ⁢
    cV
    ⁢
    
      
        d
        T
      
      
        d
        t
      
    
  
  =
  
    
      Q
      rxn
    
    -
    
      hA
      ⁡
      
        (
        
          T
          -
          
            T
            bulk
          
        
        )
      
    
  




where Qr×n is the heat generated by the chemical reaction, ρ is the density of the thermopile metals, c is the heat capacity of the thermopile metals, V is the volume of the metals, h is the heat transfer coefficient, and A is the cross-sectional area of the thermopile, which is the length multiplied by the width.

While the heat generation term may be sum of heats generated by a series of reactions, for this example, we assume that it is the heat generated by the acetone-interactant reaction only. Therefore,




  
    Q
    rxn
  
  =
  
    
      
        N
        ·
        Δ
      
      ⁢
      
        
      
      ⁢
      H
    
    =
    
      
        
          [
          
            
              1
              5
            
            ·
            
              
                D
                
                  2
                  /
                  3
                
              
              
                v
                
                  1
                  /
                  6
                
              
            
            ·
            
              
                
                  C
                  bulk
                
                ·
                
                  Q
                  
                    1
                    /
                    2
                  
                
              
              
                
                  (
                  
                    x
                    ·
                    W
                    ·
                    h
                  
                  )
                
                
                  1
                  /
                  2
                
              
            
          
          ]
        
        ·
        Δ
      
      ⁢
      
        
      
      ⁢
      H
    
  




And, the heat transfer coefficient is commonly correlated using the Nusselt number:





  Nu
  =
  
    
      
        
          h
          
            :
            L
          
        
        ·
        L
      
      k
    
    =
    
      0.332
      ·
      
        Re
        L
        
          1
          /
          2
        
      
      ·
      
        Pr
        
          1
          /
          3
        
      
    
  




where k is the thermal conductivity, L is the length over which it is desirable to compute the average heat transfer coefficient, and Pr is the Prandtl number, which is equal to the kinematic viscosity divided by the thermal diffusivity. Rearranging terms,





  
    h
    L
  
  =
  
    0.664
    ·
    k
    ·
    
      Pr
      
        1
        /
        3
      
    
    ·
    
      
        u
        
          v
          ·
          L
        
      
    
  




Substituting the flow rate for the velocity, we get:





  
    h
    L
  
  =
  
    
      0.664
      ·
      k
      ·
      
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          1
          /
          3
        
      
      ·
      
        
          Q
          
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            ·
            L
            ·
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            ·
            h
          
        
      
    
    =
    
      0.664
      ·
      k
      ·
      
        
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          v
          
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            /
            2
          
        
      
      ·
      
        Q
        
          1
          /
          2
        
      
      ·
      
        
          1
          
            L
            ·
            W
            ·
            h
          
        
      
    
  




Accordingly,





  
    ρ
    ⁢
    
      
    
    ⁢
    cV
    ⁢
    
      
        d
        T
      
      
        d
        t
      
    
  
  =
  
    
      
        
          [
          
            
              1
              5
            
            ·
            
              
                D
                
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                  /
                  3
                
              
              
                v
                
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                  /
                  6
                
              
            
            ·
            
              
                
                  C
                  bulk
                
                ·
                
                  Q
                  
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                    2
                  
                
              
              
                
                  (
                  
                    x
                    ·
                    W
                    ·
                    h
                  
                  )
                
                
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          ]
        
        ·
        Δ
      
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          (
          
            T
            -
            
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              bulk
            
          
          )
        
      
    
  




We are performing this analysis to gain an understanding of the optimal flow rate range. Therefore, we lump the parameters together as follows:





  
    
      d
      T
    
    
      d
      t
    
  
  =
  
    
      
        K
        1
      
      ·
      
        Q
      
    
    -
    
      
        K
        2
      
      ·
      
        Q
      
      ·
      
        (
        
          T
          -
          
            K
            3
          
        
        )
      
    
  




The solution to this differential equation is of the form:





  T
  =
  
    
      1
      
        K
        2
      
    
    ·
    
      (
      
        
          K
          1
        
        +
        
          
            K
            2
          
          ⁢
          
            K
            3
          
        
        +
        
          e
          
            
              -
              
                (
                
                  t
                  +
                  d
                
                )
              
            
            ⁢
            
              (
              
                
                  K
                  2
                
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      )
    
  




where d is the integration constant.

This solution yields multiple conclusions. First, if we assume that the temperature of the reference junctions is constant or unaffected by the heat generated by the interactant-analyte enthalpic process, the temperature signature aforedescribed is actually of the same form as the temperature difference, which the thermopile converts to the output voltage.
From this response, we see that the temperature signature varies as a function of flow rate. Generally, as the flow rate increases, the temperature of the thermopile sensing junction decreases. Therefore, if a continuous signal is being measured, it is desirable to maintain low flow rates over the sensor.
However, at steady state or at maxima or minima (situations where dT/dt=0), the temperature response is independent of flow rate. Therefore, if the flow rate is controlled such that convection does not dominate over diffusive mass transport to the surface, it may be desirable to select signal features, such as the maximum, minimum, or steady state response, when attempting to determine concentration levels.
Moreover, if the concentration level is determined from the maximum, minimum, or steady state value, it will be possible to plug this value into the equation and, using other values, compute the flow rate of the air stream.
This model is limited in some circumstances by the fact that the flow rate was assumed to be constant with time. If the flow rate was in fact changing as a function of time, as one skilled in the art would appreciate, the solution to the above differential equation can be modified.
As may be appreciated, under certain circumstances, to determine the concentration of the one or more analytes, it may be desirable to process the signal from the thermal sensor considering other factors, such as flow rate and temperature. This can be done in various ways. For example, the overall device may include a temperature measurement unit and a flow measurement unit which, like the thermal sensor, are coupled to a processor. Or, the signal itself may be processed using an algorithm, where certain signal features aid in determining the flow rate and/or temperature, and these parameters may, in turn, aid in interpreting an aspect of the signal so as to determine the overall concentration.
Packed beds may also be used with thermal sensors so as those that have been described herein. In the embodiment shown in FIG. 39, the analyte interactant 284 is immobilized within a packed bed 283 which is placed over the thermal detector 281 (e.g. the pyroelectric detector, thermopile, etc). The analyte 282 passes through the packed bed 283 and binds to the analyte interactant 284 in an enthalpic process which is measured by the thermal detector 281.
Under certain circumstances, use of a packed bed embodiment may be desirable. For example, if the flow rate is high, convection may dominate over diffusion to the surface, which could limit the efficacy of surface reactions. If the length of the packed bed is appropriately determined based on residence times, etc, it can ensure that all of the analyte has had an opportunity to interact with the analyte interactant within the packed bed. As a second example, if the concentration of analyte is high, a packed bed will increase the surface area for an interaction to occur.
The packed bed may be any material that can be linked to the analyte interactant. Examples may be or comprise microspheres or nanoparticles, which could be made of, for example, polymeric materials, silica, or metallic compounds.
Depending on the packing structure of the bed, the packed bed may serve as a filter based on size exclusion principles.
In the embodiments generally described by FIG. 38 and FIG. 39, the predominant mode of heat transfer to the thermal detector is conduction. However, thermal detectors can also measure heat transferred via radiation. FIG. 40 exemplifies an embodiment that utilizes a thermal detector 294 to measure radiated heat that is generated from an enthalpic interaction between an analyte 290 and an analyte interactant 291.
Turning to the subject of temperature compensation, ideally speaking, an ideally designed and manufactured thermopile should exhibit common mode rejection and therefore any thermal changes in the environment should be simultaneously and equally experienced by the reference and sensing junctions thereby producing an output voltage of zero. However, under certain circumstances, the thermopile may register a non-zero voltage due to environmental conditions. Some of these conditions are described as follows: (a) the junctions are not perfectly balanced and therefore the thermopile does not have a common mode rejection ratio equal to one, and/or (b) there are major temperature fluctuations in the environment. To solve either of these or related problems, a temperature compensating unit may be used. One example of this temperature compensating unit is a “reference thermopile,” which would serve to quantify any type of imbalance between the sensing and reference junctions.
FIG. 35 shows an embodiment according to another aspect of the invention that utilizes a temperature compensating unit. The gas containing the analyte 240 passes through a conduit where the top contains an interactant 242 that is specific for an interfering substance and the bottom contains an interactant 241 that is specific for a second interfering substance. The gas then comes in contact with a temperature compensating unit 243 which is coupled to the microprocessor 244. The microprocessor interprets the signal from the sensor 245 considering the signal from the temperature compensating unit. Based on both of these inputs, the microprocessor then produces an output that is descriptive of the concentration of the analyte.
In some instances, it is desirable to regulate the flow rate of the gas, strip the air of any moisture or water droplets, and account for temperature when considering the signal response. FIG. 33 shows a block diagram of a preferred embodiment of the invention when exposed to an analyte of interest. The user exhales a gas containing the analyte 220 into a disposable mouthpiece 221 which passes through a flow direction unit 222. The flow direction unit serves either or both of the following functions: (a) ensures that only a deep lung sample of air is allowed to pass through the remaining components and (b) ensures that flow is in one-direction only. Next, the gas passes through a pressure relief valve 223 which may contain some sort of continuous feedback, such as a whistle, to make certain that the user is blowing hard enough into the device. For example, the whistle may sound if the user is generating greater than 2 psi. The gas then passes through a moisture filter 224 which may have an inherent pressure drop thus serving to decrease the flow rate of the gas, which may be advantageous. Drierite could be used as the moisture filtration material. For example, in some embodiments, a flow rate of around 100 mL/min is preferable. If necessary or desirable, the gas may pass through a temperature-related apparatus 225. This apparatus can do any of the following functions: (a) serve to account for imbalances between the reference and sensing junctions of the thermopile, (b) measure the absolute temperature of the incoming gas stream, and/or (c) bring the temperature of the incoming gas stream to approximately the same temperature as the device itself. The gas then passes through the sensor housing 226 where it contacts the sensor. The output of the sensor is in some fashion presented on a display 227.
In some instances, it may be necessary or desirable to collect a breath sample in some type of collection bag, such as a Tedlar bag. This may be advantageous for calibration purposes. FIG. 34 presents an embodiment according to another aspect of the invention that is amenable to use with a collection bag. Some type of flow-inducing device 230, which may be as simple as a book placed atop the collection bag 231, causes the gas containing the analyte contained within the collection bag to pass through a flow restrictor 232, a moisture filter 233, a temperature-related apparatus 234, and then the sensor housing 235. The output of the sensor is in some fashion presented on a display 236.
FIG. 24 shows an illustrative example of a device encasement, the top piece of which comprises a mouthpiece 173, a display 171, buttons 172 and surface. The top piece is attached to the bottom piece via two fasteners 177, which may include magnets, screws, or the like. The thermal sensor may be placed in a cavity 174 with leads exiting the device through one or two holes 175 or 176. The exiting leads may or may not be desirable, depending on the application. FIG. 25 shows a perspective diagram of the encasement shown in FIG. 24. FIG. 27 shows how the thermal sensor of this embodiment 190 may be placed into the bottom piece of the encasement 191. FIG. 28 shows that the embodiment of FIG. 24 may be used in conjunction with filters 201 and/or restrictors 202.
FIG. 36 shows another example of a device encasement 250.
Example 1
FIG. 54 shows an embodiment that utilizes a pyroelectric detector 435. The analyte 437 passes through a conduit and interacts with an analyte interactant 432 which is immobilized on a test strip 431. The test strip 431 is passed through the conduit by a mechanism 434, such as a gear, motor, etc, and is guided by a strip director 433. The output of the pyroelectric detector 435 is processed by a signal processing unit 436.
As a general matter, the response of thermal sensors is improved by use of thin-film materials. In some instances, if the expected signal is large, the magnitude of the signal is perhaps not an issue. However, the thermal time constant (i.e. the response time) is typically impacted if the heat capacity is high. Accordingly, under most circumstances, it is desirable to employ thin-film materials. With this type of test strip embodiment, to ensure good thermal contact, it is desirable if the test strip is in good mechanical contact with the sensor.
A specific example of this embodiment uses a 9 μm polyvinylidene fluoride (PVDF) film that is coated on both sides with NiAl to serve as electrodes. The film can be cut using a razor blade or ceramic scissors to a 1 cm×1 cm surface area. Electrical contact will be made via the electrodes to shielded wire. This film is immobilized onto a bottom piece of a flow chamber. Between the leading edge and the sensor, a cover piece will be mounted atop the bottom piece of the flow chamber that will serve as a test strip director. The bottom piece will have an opening under which a microgear and gear belt will be located to facilitate moving the test strip through the test strip director and over the sensor to allow for the desired interactions.
The test strip is not limited to a particular material. In this example, a polyester film such as Mylar is used. The Mylar will be cut into 1 cm×10 cm strips. The location of the analyte interactant will be noted using print-on demarcations. The analyte interactant will be patterned in an alternating fashion with a void space. In this way, when the analyte interactant is exposed to the fluid, heat may be generated (if the analyte is present), and this heat will be measured by the detector. When the portion of the test strip without analyte interactant is exposed to the fluid, there will be no heat generated (or solely noise, interfering signals, and non-specific adsorption will be measured and serve as a reference).
The flow chamber shown in FIG. 54 is, of course, only one example of such a flow chamber. In the event that the desired thermal contact between the test strip and the pyroelectric sensor cannot be made, it is possible to use pyroelectric ribbon as the test strip itself and pattern the analyte interactant directly onto the ribbon, which would require moving the ribbon through the sensor. Or, to provide mechanical rigidity, the entire bottom plate may be moved simultaneously with the test strip.
This embodiment may be used to measure glucose concentrations using, for example, glucose oxidase as the analyte interactant. Glucose oxidase (2 mg, Type VII, 137 units/mg) is mixed with a glutaraldehyde cross-linking agent (1 μL, 25%) and mixed for 15 seconds. This gel is applied evenly over the surface of the test strip and allowed to cure. A photomask with alternating blocked/unblocked portions is placed over the test strip and the exposed portions of the test strip are irradiated to inactivate the enzyme. In this manner, the thermal load of the test strip is constant throughout. It is possible, of course, to only coat the gel onto the desired parts of the test strip (instead of the entire strip) to avoid the irradiation step.
To test the performance of the sensor, solutions containing 10 mM pH 7.4 phosphate buffer solution with varying glucose concentrations (25, 50, 75, . . . , 250 mg/dL) can be prepared and stored in 1 L flasks. The fluid may be pumped from the flask and into the flow chamber using a fluid pump from a suitable source.
Depending on the embodiment and the knowledge of the chemistry, it may or may not be helpful to perform control experiments. If it is, examples of control experiments are provided. The first control experiment will measure the background noise of the pyroelectric sensor to flowing fluid. The second will measure the output of the pyroelectric sensor to the moving test strip in a flowing fluid. If an unexpected result occurs, this ought to be well-characterized and, in future experiments, subtracted from the test signals.
Example 2
In this example, a thermal sensor for oligosaccharide detection is described. Oligosaccharides (“glycans”) are associated with various pathologies, including cancer. These oligosaccharides may be found on the periphery of the cell on the glycocalyx. They also may be found free flowing in blood attached to biomolecules such as proteins. During disease states, the concentration of glycans may increase, the structure of the oligosaccharide may be modified or altered, or neoexpression of certain glycans may occur. Accordingly, measuring glycans can serve as tremendous biomarkers.
Although sugars are well-known as the “third language of life” (genomics, proteomics, glycomics), because glycoscience is an emerging field, it is important to understand why it is important to measure glycans. First, in some instances, glycans have served as biomarkers where other disease markers have not been identified or are limited (e.g. in multiple sclerosis). Second, many papers have shown that even when the protein concentration remains the same, “the structure of its carbohydrate chains also changes, in particular, the branching, the degree of sialylation, and the number of terminal [sugar residues].” Thus, even if the protein structure remains the same, the carbohydrate chains on a given biomolecules or cell may be altered and indicate pathology.
Oftentimes, particularly for measurement of biological analytes, it is desirable to employ an aptamer as the analyte interactant. This example provides an example method for selecting an aptamer for a glycoprotein known as α1-Acid glycoprotein (AGP), which is found under normal conditions in concentrations such as 0.2-1 mg/mL. AGP is an acute phase glycoprotein that is approximately 43 kDa in size and has five N-linked glycans on the surface of the protein. During pathology, such as cancer, these concentrations increase multiple-fold. Also, there are changes to the fucosylation and/or sialylation index of the carbohydrate chains.
SELEX is an iterative technique that aids in identifying high affinity analyte interactants (e.g. aptamers) to target molecules. The SELEX process can include a negative control step to aid in identifying an aptamer which not only binds to the target glycan with high affinity but also discriminates against known interfering substances. Also, if desirable, this process can be used to identify an aptamer that is cross-reactive between molecules with similar characteristics.
In this example, an aptamer library ( ̃1017 oligonucleotides) with 80 base pairs is created. Thereafter, the standard SELEX process is used and the non-binding RNA sequences are filtered via elution using a nitrocellulose filter. Because of the application, the following modifications are made to the procedure. Once the aptamer library has been reduced ( ̃5 steps), a negative control step is performed against interfering substances where the eluted RNA sequences, instead of being discarded, are amplified for the remainder of the screenings against AGP. In this way, similar oligosaccharide structures on non-AGP protein structures will be minimized. The last  ̃102 RNA sequences that have been identified as high affinity aptamers will be saved for further analysis. However, the refinement will continue until we have identified a single aptamer candidate.
There are other forms of SELEX including, CE-SELEX, Toggle-SELEX, tailored-SELEX, and others. If glycans that are attached to transmembrane proteins of cells are desired to be measured, CE-SELEX may be the appropriate technique to use. Also, while aptamers are extremely robust molecules, under certain circumstances and for certain aptamers, they can be broken down by nucleases. There are aptamers that can be modified to increase their stability. For example, spiegelmers that mirror the sequence of the selected aptamers can be synthesized. Because most spiegelmers employ L-ribose instead of D-ribose, they are resistant to nuclease degradation. If spiegelmers do not help the potential aptamer-degradation problem, it may help to pre-treat the fluid containing the analyte by heating to deactivate enzymatic activity. Also, during the synthesis step, it may be desirable to biotinylate the aptamers so that it is not necessary to perform this step post-synthesis for immobilization purposes.
Affinity and specificity are different properties. High affinity does not necessary imply high specificity. In this regard, it is advantageous to note that SELEX identifies high affinity ligands. The specificity of final aptamers may be improved by a negative control step in SELEX. Or, the final  ̃100 aptamer sequences identified via SELEX can be screened against interfering substances and the AGP to test for specificity. This can be done using an aptamer array.
These aptamers (biotinylated during synthesis) can be incubated separately with streptavidin agarose beads to form aptamer beads. The aptamer beads are then loaded into rectangular wells of a 10×10 chip.
For glycans, interfering substance (negative controls) can be determined by altering any of the following: (1) the terminal sugar linkage, (2) the terminal or near-terminal sugars themselves, and (3) a combination of these. For AGP, for example, (Fucα1,2)Galβ1 . . . -conjugated BSA and/or (NeuAcα2,4)Galβ1 . . . -conjugated BSA may be used as negative controls.
The AGP and the negative controls can be fluorescently tagged with an Alexa-Fluor label. It may be easier to tag the proteins than the aptamers because of the size differential but this depends on the structure. The AGP independently is contacted with the chip for a period of 4-6 hours and the fluorescence level is measured. The same procedure is repeated with the negative controls. Aptamers that bind to AGP exclusively or to a greater extent than the negative controls are selected. If no aptamers meet this criteria, a decision is made as to whether to reperform SELEX or attempt to filter out interfering substance before exposure to the sensor.
Of course, aptamers can be used in conjunction with a number of different sensors. If a pyroelectric sensor embodiment that utilizes a test strip is used, the following are examples for patterning the test strip. For example, in one test strip, the aptamer is covalently bonded to a gold-plated pyroelectric ribbon test strip. The aptamers will undergo a thiol-modification and the Au plated pyroelectric ribbon will be functionalized with sulfo-SMCC, which has an NHS ester group to covalently bond to amine-activated Au and a maleimide group to bind with the aptamer.
In a second example, a thin plastic such as Mylar that has been coated with streptavidin may be used as a test strip. The aptamers, which may be biotinylated during synthesis, bind to the streptavidin. It is usually advantageous to completely saturate the streptavidin binding sites to minimize any errors from test strip to test strip.
In this example, the aptamers may be patterned to the test strip in a variety of different ways including using a copper metal mask. In this case, a copper metal mask will be micromachined with holes in the locations where the aptamers are to be immobilized. This mask will be fastened to the test strip and the combination of the top portion of the test strip and mask is coated with streptavidin for surface treatment. Once the streptavidin has cured, the test strip is unclamped from the mask and the strip is immersed in a solution containing three times the necessary concentration of the aptamer. After sufficient time for binding to occur, the test strip is rinsed with an appropriate buffer solution. This procedure is repeated at least twice to ensure complete saturation of all reaction sites. If the difference in thermal load of the void-aptamer spots becomes an issue, it may be necessary to coat the non-aptamer binding surfaces with a non-binding aptamer so that surface make-up is similar through the test strip.
It is advantageous to note that this technique can be modified for measuring multiple glycans or, in general, multiple analytes. Or, alternatively, if multiple aptamers are employed to specifically identify a single glycan, an array-based test strip may be developed. In this situation, instead of the test strip simply moving in one direction to allow for modulation, the test strip would be moved back and forth between the void spaces and the spaces containing an aptamer. To create this array, the automated robotic processes used in microarray technology may be employed to spot aptamer onto a surface. Depending on the number of aptamers to be patterned, the microwell technique described earlier may also be used. An array of sensors may also be necessary.
Turning again to the use of aptamers as analyte interactants, there are many benefits to using an aptamer. Aptamers can be stable and reusable and they may be easy to immobilize. Perhaps the greatest advantage, however, is that selectivity can be achieved. Because of the number of aptamers that can readily be synthesized, identifying one or more aptamers that will serve to identify the presence of a particular analyte can be achieved.
The following is an example of how an aptamer interactant may be used. The thermopile metals are deposited onto a substrate. The substrate, in this case on the side opposite the metals, is protected except for the area over the thermopile sensing junctions (“surface”). The non-protected surface is functionalized such that aptamers can bind directly to it or, alternatively, nanobeads containing the aptamer are deposited over this surface. When the analyte passes over the sensing junctions of the thermopile, the analyte binds to the aptamer. This binding phenomenon produces heat, which is measured by the thermopile.
To increase the amount of heat generated by the interaction of the analyte and the aptamer, the aptamer can be designed to have multiple binding sides. Additionally, if the aptamer is immobilized onto silica beads or nanobeads, this increases the effective number of molecules available for reaction per unit surface area, which in turn increases the amount of heat that is generated.
Typically the analyte is adsorbed onto the aptamer. Therefore, the analyte can be released in a short period of time by promoting desorption by, for example, increasing the temperature of the surface on which the aptamer is bound. In this way, the sensor with immobilized aptamer can be reused multiple times.
In the event that the analyte is too small to bind between within the aptamer, the analyte may be pre-treated within the overall device to selectively attach it to a larger molecule such as, for example, a fluorophore.
Example 3
FIG. 61 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment comprised an Fe2O3 nanoparticle sensor. This sensor was tested in an environment with a continuous stream of gas (500 SCCM) mixed from compressed sources via mass flow controllers (to final percent volumes of 18% O2, 3% CO2, ppm levels of acetone, balance N2). Under dry, continuous gas streams, the sensitivity of the nanoparticle sensors to acetone is very high and stable.
FIG. 62 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment comprised an Fe2O3 nanoparticle sensor. This sensor was tested with moderate amounts of humidity (20% RH at 37 deg C.) added to the continuously supplied simulated breath (18% O2, 3% CO2, ppm levels of acetone). The sensor response to even moderately high acetone concentrations (2 ppm in the figure) are severely impaired. The humidity chamber created a constant supply of 20% RH at 37 deg C. (roughly 40% RH at 25 C) with a 3% fluctuation band. Humidity is shown to be a significant deterrent of acetone detection using the nanoparticle-based sensor without humidity mitigation strategies.
FIG. 63 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment comprised an Fe2O3 nanoparticle sensor. The sensor was tested in a flow chamber with 21% v/v O2 and then flow was stopped for a few minutes, simulating an operating mode whereby a hand-held sensor would be warming up in preparation for a breath sampling event. Then, the gas concentration was set at 18% O2 and 3% CO2, balance N2, with acetone spikes where indicated. The sensor response to zero flow switched to sample flow (500 SCCM) with a concurrent change in O2 concentration was dramatic. Sensor response to 5 ppm administrations of acetone are not visibly discernible under these pulsatile flow conditions. Immediately following the simulated breath sample, the sensor chamber was flushed with 21% 02 in preparation for another resting state. Pulsatile flow is shown to be a significant deterrent of acetone detection without using flow and pressure mitigation strategies. Also, the sensitivity of the nanoparticle sensor to changes in oxygen concentration are strong, a fact that complicates breath analysis using semiconductor nanoparticles.
FIG. 64 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment comprised an Fe2O3 nanoparticle sensor, using a conditioning device. The response of the sensor element to the various stages of breath sampling, as described in FIG. 55, is shown in FIG. 64. Arrows indicate the time point wherein the three-way valves switch to allow the carrier gas to deliver the analyte to the sensor element. The sensitivity trace upstream of the arrow indicates a portion where a blank sample is administered to the sensor element, allowing the collection of baseline data. The sensitivity trace after the switch shows the sensor response to the gas stream with the swept analyte. After the artifact of switching passes, a downward deflection in the sensitivity is observed. The downward deflection caused by a 2 ppm analyte concentration is noticeably larger than that caused by the 0 ppm sample.
FIG. 65 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment again utilizes an Fe2O3 nanoparticle sensor and a conditioning device. A data processing scheme is presented and utilized for creating a dose response curve from the raw data traces as presented in FIG. 64. The last data point before the carrier gas switch-over is used for data normalization, a procedure which effectively removes minor baseline drifts. FIG. 65 was created by analyzing the raw traces from a blank breath sample (no acetone), a 2 ppm sample, another blank, and then a 0.7 ppm sample, separated by several minutes. The simulated breath consisted of 40% RH (at 37 C), 18% O2, and 3% CO2 (balance nitrogen). 400 cc's of simulated breath were administered to the capture and release scheme, without the use of the first sample conditioning column (moisture removal column). Use of the moisture removal column enhances the sensor performance. The data presented in FIG. 65 represents the response of a nanoparticle-based sensor to acetone in simulated breath with characteristics that mimic human breath samples.
FIG. 66 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to oxygen. This embodiment again utilizes an Fe2O3 nanoparticle sensor and a conditioning device. The conditioning device is comprised of a calcium chloride desiccant (5 g). The oxygen was varied under a steady flow (500 SCCM) at RH of 40% at 37 C (equivalent to roughly 80% RH at room temperature). The concentration of oxygen in the gas stream was varied between 18, 24, and 12% v. FIG. 66 demonstrates the ability of a nanoparticle-based sensor to measure oxygen in the presence of humidity.
FIG. 67 is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to isopropyl alcohol. This embodiment uses a SnO2 nanoparticle sensor. Carrier gas consisting of 18% v oxygen, 3% v CO2, and a balance of nitrogen was alternately passed through the head space of two vials holding different mixtures of alcohol and water held at room temperature. The first arrow indicates the time when carrier gas flow was switched from a vial containing 0.225% v isopropanol in water to a vial containing 0.125% v isopropanol in water. Flow was subsequently alternated between the two vials a few times. Then, the vial containing 0.125% v isopropanol in water was diluted to hold 0.0625% v isopropanol in water. The second arrow indicates the first time that flow was directed through the vial containing 0.0625% v isopropanol in water. Flow was subsequently switched a few times between the vial with 0.0625% v isopropanol in water and the vial with 0.225% v isopropanol in water.
In certain instances, once the thermal sensor has been exposed to the gas containing the analyte, it may be necessary to purge the conduit of the gas. This may be necessary for a variety of reasons. For example, in breath analysis, especially if the breath has not been stripped of moisture or bacteria, it may be advantageous to remove any residual water/bacteria from the thermal sensor and/or the conduit so as to prevent corrosion or contamination.
Purging the conduit can also allow for reverse reactions or physical phenomena to occur, which may help to bring the overall system back to equilibrium. For example, if an adsorption interactant were selected, exposure to the analyte will promote adsorption, but exposure to a purging gas stream may help promote desorption.
Purging can also help promote reverse reactions. For example, consider the following reaction A+B←→C+D, where A is the analyte and B is the analyte interactant. If A is present in high concentrations (because, for example, a gas containing A is passed through the conduit), the net reaction will proceed in the forward direction. This will result in a build-up of C and D and a complete or partial consumption of B. If, then, A is removed from the system (either because there is no input to the conduit or because an input containing no A is input), the reverse reaction will proceed, which will result in replenishment of B.
In other instances, prior to exposure to the gas containing the analyte, it is advantageous for the analyte interactant to be exposed to a priming stream. For example, water may be passed through the conduit to allow water and the immobilized interactant to react, thereby forming a species that will interact with the analyte of interest. This is particularly desirable when an interactant is selected because it is stable, but perhaps can be activated to become truly reactive with the analyte.
It may also be desirable to utilize a priming stream to establish the temperature and flow regime. For example, if the overall device is placed in an environment where the environmental conditions are substantially different than those of its prior use, a priming stream may be helpful to calibrate the device.
FIG. 26 shows a structure/function diagram of an embodiment.
In accordance with another aspect of the invention, a method for raw signal interpretation is provided. This method may be implemented in computer software. Depending on the application, different features of the signal from the thermal sensor may indicate the presence or concentration of the analyte. A new and useful method for processing this signal is as follows.
A baseline is calculated for a period of time such as 5 seconds. Following the computation of this baseline, the maximum and minimum values are stored. The absolute values of the maximum and minimum values received from the thermal sensor are compared. The greater value is called the peak value. The raw signal is defined as or set to be equal to the peak value minus the baseline. The raw signal then is converted into a displayable value, for example, based on a predetermined calibration chart or look-up table. This method can be illustrated as follows:
Once the “START TEST” button is pushed:
(1) Display “Wait . . . ”
(2) Calculate BASELINE (average over first 5 seconds, approx 40 pts)
After 5 seconds:
(3) Display “Testing . . . ”
(4) Store MAX and MIN
After 20 seconds:
(1) Compare abs(MAX) and abs(MIN); whichever is greater=PEAK;
Note that PEAK can only take on (+) values
(2) Compute: PEAK−BASELINE=RAW
(3) Access look-up table; convert RAW to VALUE
(4) Display “Your Value is: VALUE”
(5) Store DATE, TIME, and VALUE to memory
Sensors according to the various aspects of the invention may be used in conjunction with supplementary or disposable/refillable components. For example, the sensor may be used with a software package that stores results of the sensor, a calibration unit, disposable/refillable cartridges of analyte interactant, or disposable filters.
Such sensors also may be used in conjunction with a calibration unit. This calibration chamber may be filled with a known quantity of air. Then a finite amount of analyte is injected into the calibration chamber and allowed to evaporate. The amount of analyte and the amount of air may be entered into a keypad or a spreadsheet to determine the concentration of the analyte. The calibration unit may then cause the calibration chamber to be exposed to the sensor. The output of the sensor may be evaluated in accordance with the concentration of the analyte so as to program the sensor.
Such sensors may also be used with disposable or refillable cartridges of analyte interactant. For instance, a test strip may be inserted into the device, said test strip containing some of the analyte interactant. These test strips may be used more than once or may be designed for single use only. Additionally, the test strips may contain multiple analyte interactants or single analyte interactants. Also, the test strips may contain interactants that complement interactants that are already on the sensor, e.g. to increase specificity and/or sensitivity.
Such sensors may be used with disposable filters. These filters may be or comprise bacterial filters, moisture filters, or filters for interfering substances.
The sensor 2 can be used in conjunction with a software package that could, via a USB cable or the like, store either the entire signal from the thermopile device or selected features therefrom. These values can be synthesized into a progress report, which may periodically be sent to a medical practitioner. Based on the progress report, the program can make suggestions for medication, lifestyle, or other changes.
Additional advantages and modifications will readily occur to those skilled in the art. For example, although the illustrative embodiments, method implementations and examples provided herein above were described primarily in terms of the conductivity or current state of the conduction paths, one also may monitor or control voltage states, power states, combinations of these, electro-optically, and the like. Therefore, the invention in its broader aspects is not limited to the specific details, representative devices and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

## Claims

1. A portable apparatus for sensing an analyte in breath, the apparatus comprising:
a breath analysis device that includes a breath input port fluidically coupled to a nanoparticle-based sensor, the nanoparticle-based sensor comprising a plurality of nanoparticles disposed on a sensing surface, the nanoparticle-based sensor configured to sense a change in an electrical property of the nanoparticles caused by the analyte; and
a mouthpiece that is removably attachable to the breath analysis device, the mouthpiece including an opening into which a user can exhale to provide a breath sample when the mouthpiece is attached to the breath analysis device, the mouthpiece including a desiccant that conditions the breath sample before the sample enters the breath input port of the breath analysis device, the mouthpiece additionally including a seal that seals the desiccant from an output end of the mouthpiece;
wherein the breath analysis device is configured to break the seal when the mouthpiece is attached to the breath analysis device.

2. The apparatus of claim 1, wherein the nanoparticle-based sensor comprises at least one of gamma Fe2O3, gamma Fe2O3 doped with TiO2, and epsilon WO3.

3. The apparatus of claim 1, wherein the nanoparticle-based sensor comprises a nanomaterial that is coupled to an electrode using at least one of heat treatment, vacuum evaporation, vacuum evaporation with heat treatment, and self-assembly using one of gaseous and liquid precursors.

4. The apparatus of claim 1, wherein the nanoparticle-based sensor is disposable.

5. The apparatus of claim 1, wherein the analyte is acetone.

6. The apparatus of claim 5, wherein the portable apparatus further comprises an interferant filter configured to reduce concentrations of interferants that interfere with the sensing of the acetone.

7. The apparatus of claim 1, wherein the breath analysis device further comprises a flushing mechanism that is configured to expose the nanoparticle-based sensor to ambient air for a period of time.

8. The apparatus of claim 1, wherein the breath analysis device further comprises a conditioning device to condition the breath sample as to flow rate.

9. A method of analyzing a breath sample of a user, comprising:
providing a mouthpiece that is removably attachable to a breath analysis device, the mouthpiece comprising a desiccant that conditions a breath sample as a user exhales into the breath analysis device through the mouthpiece, the desiccant protected by a seal;
forming a flow path between an opening in the mouthpiece and a breath input port of the breath analysis device, wherein forming the flow path comprises breaking the seal;
receiving a conditioned breath sample into the breath analysis device, the conditioned breath sample conditioned by the desiccant in the mouthpiece; and
sensing an analyte in the conditioned breath sample with a nanoparticle sensor of the breath analysis device, the nanoparticle sensor comprising a plurality of nanoparticles disposed on a sensing surface, the nanoparticle sensor configured to sense a change in an electrical property of the nanoparticles caused by the analyte.

10. The method of claim 9, wherein the nanoparticle-based sensor comprises at least one of gamma Fe2O3, gamma Fe2O3 doped with TiO2, and epsilon WO3.

11. The method of claim 9, wherein the nanoparticle-based sensor comprises a nanomaterial that is coupled to an electrode using at least one of heat treatment, vacuum evaporation, vacuum evaporation with heat treatment, and self-assembly using one of gaseous and liquid precursors.

12. The method of claim 9, wherein the nanoparticle-based sensor is disposable.

13. The method of claim 9, wherein the analyte is acetone.

14. The method of claim 13, further comprising filtering to reduce concentrations of interferants that interfere with the sensing of the acetone.

15. The method of claim 9, further comprising flushing the nanoparticle-based sensor to expose the nanoparticle-based sensor to ambient air for a period of time.

16. The method of claim 9, further comprising conditioning the breath sample as to flow rate.