Patent Publication Number: US-2020281504-A1

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

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     This application claims the benefit of U.S. application Ser. No. 15/156,188, filed May 16, 2016, which is hereby incorporated by reference in its entirety herein. This application claims the benefit of U.S. Provisional Application No. 62/161,872, filed May 14, 2015, which is hereby incorporated by reference in its entirety herein. Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 C.F.R. § 1.57. 
    
    
     FIELD 
     The present disclosure relates to breath measurement or analysis systems, devices and methods for measuring acetone in breath and, more specifically, to breath measurement systems, devices and methods that employ nanoparticle-based sensors. 
     BACKGROUND 
     Breath analysis for measuring chemical components or analytes in the breath offers important potential benefits over other alternative methods of analyte measurement, e.g., such as blood- or urine-based measurement. Such benefits include ease of use and patient or user compliance, particularly for home or other non-clinical use. Gaining patient compliance is generally far easier when the requirement is to exhale into a device, rather than drawing blood or obtaining a urine sample. Ease of handling the samples also is enhanced. 
     Hand-held or otherwise portable breath analysis devices afford the potential for even greater advantages. Such portability presents opportunities for extra-clinical applications, e.g., at home, office, gym, weight loss facility, and the like, and by the patient or user himself or herself, rather than by a trained clinician or technician. Portable breath sensing systems offer the potential for comfortable and more natural sampling to increase user adherence to a desired sampling schedule. 
     Although approximately 300 analytes have been identified in human breath, acetone is an important analyte that is particularly promising for practical and beneficial application. Acetone has been correlated with fat metabolism, which in turn is involved in physiological and pathophysiological phenomena ranging from weight loss to metabolic disorders. Measurement of breath acetone at levels or concentration ranges of interest, for example, can enable one to gain useful information about such factors as patient or user weight loss, and about such pathological states as diabetes mellitus, metabolic syndrome, and metabolic or ketoacidosis. 
     SUMMARY 
     The sensor can be a central component in portable breath analysis devices. The analyte or analytes of interest in breath analysis often are present only in very low concentrations, thus requiring highly sensitive sensors. The sensing task is made more difficult by the fact that, as noted above, breath typically has a range of chemical components in it, including a range of volatile organic compounds. In addition, breath is typically at or near saturation with humidity. These concerns and the plethora of potential inteferents make accurate and reliable detection of the target analyte challenging. 
     A variety of sensor technologies are known or have been theorized. Examples include thermo-electric sensors, pyroelectric sensors, electrochemical and enzyme sensors, and colorimetric sensors. Each of these sensor technologies has its own set of advantages, disadvantages, limitations and challenges. 
     With some sensor technologies, the sensor must be heated from a power or heat source prior to and as part of its operation. In the context of portable breath measurement devices, this usually requires that electrical circuitry and a suitable power source be provided. 
     In some portable breath measurement devices, the user positions the breath measurement device in contact with his or her mouth and exhales directly into the device. Where the sensor is heated, for example, as may be required with nanoparticle-based sensors, this places the heated sensor in fluid communication with the user&#39;s mouth and respiratory tract. In addition to the unwanted transfer of heat, such devices can present chemical toxicity risks. Electrical aspects of the breath measurement devices also can pose risks. Electrical anomalies can arise, for example, such as electrostatic discharge, power surges or spikes, overvoltage or overcurrent conditions, radiation, and the like. Thus, there is a need for breath measurement systems, devices and methods, and particularly breath measurement systems, devices and methods comprising nanoparticle-based sensors, for safety-related enhancements. 
     This disclosure includes a portable measurement device for measuring acetone in a breath sample of a user. The measurement device comprises a housing, a user-direct breath input device for engaging in direct fluid communication with a respiratory tract of the user and receiving the breath sample from the respiratory tract, a flow path disposed within the housing and comprising an upstream end and a downstream end, the upstream end of the flow path being in fluid communication with the user-direct breath input device, wherein in normal operation of the device the flow path directs the breath sample in a downstream direction from user-direct breath input device at the upstream end of the flow path and toward the downstream end, and a nanoparticle-based sensor disposed in the housing in fluid communication with the flow path and at an intermediate location between the upstream end and the downstream end. The device can further include a flow control device disposed in the housing and in the flow path between the upstream end and the nanoparticle-based sensor that prevents flow of the breath sample in an upstream direction opposite the downstream direction. 
     The user-direct breath input device may comprise a mouthpiece, a face mask, a nasal airway, and/or the like. The nanoparticle-based sensor can be disposed within the housing so that the nanoparticle-based sensor is substantially inaccessible to the user during use of the device. The intermediate location can include a compartment within the housing that comprises a detachable cover at an external location on the housing, and wherein the detachable cover is secured in a closed position. The detachable cover can include a fastener that requires a tool to detach from the housing. 
     In one embodiment, the housing comprises an insertion aperture, and the nanoparticle-based sensor can be disposed on an insertion member that can be inserted into and detached from the insertion aperture. 
     The flow control device may include at least one one-way valve, or at least two one-way valves. The one-way valve can be disposed adjacent to the breath input device. The one-way valve can be disposed at the upstream end of the flow path or, alternatively or in addition, the one-way valve may be disposed between the upstream end of the flow path and the intermediate location. 
     The measurement device can include a conditioning device disposed in the flow path between the upstream end of the flow path and the intermediate location, for example, disposed adjacent to the user-direct breath input device and/or disposed between the user-direct breath input device and the nanoparticle-based sensor. 
     The measurement device can include a conditioning device. The conditioning device can be disposed in the flow path downstream from the one-way valve and between the one-way valves if there is more than one. In either event, the conditioning device can be disposed in the flow path between the upstream end of the flow path and the nanoparticle-based sensor. Where there is a user-direct breath input device, the conditioning device can be disposed adjacent to the input device. 
     The measurement device can include a processor operatively coupled to the nanoparticle-based sensor for receiving a measurement signal representative of a concentration of the acetone in the breath sample from the nanoparticle-based sensor, and a communications device operatively coupled to the processor that receives the measurement signal from the processor and communicates the measurement signal externally from the measurement device. 
     In accordance with another aspect of the disclosure, a method is provided for sensing acetone in a breath sample of a user. The method can comprise providing a measurement device that comprises a housing, a flow path disposed within the housing, wherein the flow path comprises an upstream end and a downstream end, a user-direct breath input device disposed at the upstream end of the flow path that engages in direct fluid communication with a respiratory tract of the user and receiving the breath sample from the respiratory tract, and a nanoparticle-based sensor disposed in the housing in fluid communication with the flow path and at an intermediate location between the upstream end and the downstream end. During exhalation of the user into the user-direct breath input device, the method comprises using the measurement device to cause the breath sample to flow in the flow path in a downstream direction from the upstream end and toward the downstream end, and to contact the breath sample with the nanoparticle-based sensor so that the nanoparticle-based sensor senses the acetone in the breath sample. During an inhalation of the user from the user-direct breath input device, the method can further include using the measurement device to prevent flow of the breath sample in the flow path in an upstream direction from the downstream end and toward the upstream end. 
     In accordance with another aspect of the disclosure, a system is provided for sensing acetone in a breath sample of a user. The system can comprise a breath bag that contains the breath sample. The system can also include a portable measurement device that in turn comprises a housing, a flow path disposed within the housing and comprising an upstream end and a downstream end, wherein in normal operation of the measurement device the flow path directs the breath sample in the flow path in a downstream direction from the upstream end and toward the downstream end, a breath input coupler disposed at the upstream end of the flow path, the breath input coupler detachably engaging the breath bag and placing the breath sample in fluid communication with the flow path, and a nanoparticle-based sensor disposed in the housing in fluid communication with the flow path and at an intermediate location between the upstream end and the downstream end. 
     The breath bag can include a one-way valve. The breath input coupler can include a valve-opening mechanism that automatically opens the one-way valve when the breath bag is engaged with the breath input coupler. The one-way valve can include a valve closure, and the valve-opening mechanism can include a post that engages valve closure and move the valve closure to an open state. 
     The measurement device can include a flow control device disposed in the housing and in the flow path between the upstream end and the nanoparticle-based sensor that prevents flow of the breath sample in an upstream direction opposite the downstream direction. 
     The measurement device can also include a conditioning device disposed in the flow path between the upstream end of the flow path and the nanoparticle-based sensor. The conditioning device may advantageously be disposed adjacent to the user-direct breath input device. 
     In accordance with another aspect of the disclosure, a portable measurement device is provided for measuring acetone in a breath sample of a user contained within a breath bag. The measurement device can comprise a housing, and a flow path disposed within the housing and comprising an upstream end and a downstream end. In normal operation of the measurement device, the flow path directs the breath sample in the flow path in a downstream direction from the upstream end and toward the downstream end. The measurement device can also include a breath input coupler disposed at the upstream end of the flow path, the breath input coupler detachably engaging the breath bag and placing the breath sample in fluid communication with the flow path, and a nanoparticle-based sensor disposed in the housing in fluid communication with the flow path and at an intermediate location between the upstream end and the downstream end. 
     In accordance with still another aspect of the disclosure, a method is provided for sensing acetone in a breath sample of a user. The method can comprise inputting the breath sample into a breath bag. It can also include providing a portable measurement device comprising a housing, a flow path disposed within the housing and comprising an upstream end and a downstream end, wherein in normal operation of the measurement device the flow path directs the breath sample in the flow path in a downstream direction from the upstream end and toward the downstream end, a breath input coupler disposed at the upstream end of the flow path, and a nanoparticle-based sensor disposed in the housing in fluid communication with the flow path and at an intermediate location between the upstream end and the downstream end. The method can further include detachably engaging the breath bag to the breath input coupler, and using the measurement device to cause the breath sample to contact the nanoparticle-based sensor and to measure a concentration of the acetone in the breath sample. 
     In accordance with yet another aspect of the disclosure, a portable measurement device is provided for measuring acetone in a breath sample of a user. The measurement device comprises a housing, a flow path disposed within the housing and comprising an upstream end and a downstream end, the upstream end of the flow path being in fluid communication with the user-direct breath input device, wherein in normal operation of the device the flow path directs the breath sample in a downstream direction from user-direct breath input device at the upstream end of the flow path and toward the downstream end. The measurement device can also include a breath input device disposed at the upstream end of the flow path for inputting the breath sample, and a nanoparticle-based sensor subsystem disposed in the housing in fluid communication with the flow path and at an intermediate location between the upstream end and the downstream end. The measurement device can further include a power source that provides power to the nanoparticle-based subsystem, and an electrical safety device operatively coupled to the power source and the nanoparticle-based sensor subsystem that protects the nanoparticle-based power from an electrical threat. 
     Where the electrical threat comprises reverse polarity, the electrical safety device can include a diode. Where the electrical threat comprises an electrical fast transient, and the electrical safety device can include a capacitor. Where the electrical threat comprises an over voltage condition, the electrical safety device can include an over voltage protection circuit, for example, such as a voltage regulator. Where the electrical threat comprises an over current condition, the electrical safety device can include an over current protection circuit. Where the electrical threat comprises an electrostatic discharge, the electrical safety device can include an electrostatic discharge mitigation circuit. 
     In some devices wherein the nanoparticle-based sensor subsystem comprises a heating device, the electrical safety device can be operatively coupled to the power supply and to the heating device to protect the heating device from the electrical threat, and/or can be operatively coupled to the power supply and to the heating device to protect the nanoparticle-based sensor from the electrical threat. 
     In various embodiments, the power supply may comprise a battery, a DC source and/or an AC source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate certain embodiments and methods of the invention and, together with the general description given above and the detailed description of the embodiments and methods given below, serve to explain the principles of the invention. Of the drawings: 
         FIG. 1  is a pictorial view of a breath acetone measurement system according to one embodiment, including a partial cutaway view of a measurement device that is part of the system; 
         FIG. 2  is a plan top view of a nanoparticle-based sensor subsystem within the measurement device shown in  FIG. 1 ; 
         FIG. 3  is a bottom view of the nanoparticle-based sensor subsystem of  FIG. 2 ; 
         FIGS. 4A and 4B  show side cutaway views of the proximal or upstream portion of the measurement device shown in  FIG. 1 , in which  FIG. 4A  is an expanded or exploded view, and  FIG. 4B  is an assembled view; 
         FIG. 5  is a longitudinal or end view of the interior of measurement device of  FIG. 1  taken in cross section along the lines  5 - 5  in  FIG. 4A  which illustrates one-way valves disposed in the measurement device; 
         FIGS. 6A and 6B  provide side cutaway views of a portion or portions of the measurement device of  FIG. 1  indicated by lines  6 - 6  in  FIG. 4A , which illustrates the operation of a one-way valve within the portion, in which  FIG. 6A  shows the valve in a closed state and  FIG. 6B  shows the valve in an open state; 
         FIG. 7  is a longitudinal or end view of the interior of measurement device of  FIG. 1  taken in cross section along the lines  5 - 5  in  FIG. 4A  which illustrates an alternative embodiment of one-way valves disposed in the measurement device; 
         FIG. 8  is a side cutaway view of a portion or portions of the measurement device of  FIG. 1 , that illustrates the operation of the one-way valve of  FIG. 7  within the portion; 
         FIGS. 9A and 9B  provides side cutaway views of a portion or portions of the measurement device of  FIG. 1 , which illustrates the operation of another one-way valve within the portion, in which  FIG. 9A  shows the valve in a closed state and  FIG. 9B  shows the valve in an open state; 
         FIG. 10  is a pictorial view of another breath acetone measurement system according to one embodiment, including a side cutaway view of a measurement device that is part of the system, in which the system comprises a breath bag for collection and delivery of the breath sample; 
         FIGS. 11A and 11B  shows side cutaway views of a portion of the measurement device of  FIG. 10  at a joinder between the mouthpiece or ferrule of a breath bag providing a breath sample and the proximal or upstream end of the measurement device, in which  FIG. 11A  shows the ferrule and proximal end of the measurement device in expanded or exploded form and  FIG. 11B  shows them in joined form; 
         FIG. 12  shows side cutaway views of a portion of the measurement device of  FIG. 10  at a joinder between proximal and distal sections of the measurement device; 
         FIG. 13  is a pictorial view of another breath acetone measurement system according to a presently preferred embodiment of an aspect of the invention, including a side cutaway view of a measurement device that is part of the system, in which the measurement device comprises a detachable nanoparticle-based sensor subsystem; 
         FIGS. 14A-14C  show an expanded view of the nanoparticle-based sensor subsystem of  FIG. 13  and a section of the measurement device into which the nanoparticle-based sensor subsystem is detachably inserted; 
         FIG. 15  is a pictorial view of still another breath acetone measurement system according to one embodiment, including a side cutaway view of a measurement device that is part of the system, in which the measurement device comprises two nanoparticle-based sensors; 
         FIG. 16  is a pictorial view of yet another breath acetone measurement system according to one embodiment, including a side cutaway view of a measurement device that is part of the system, in which the system comprises a non-linear flow path; 
         FIG. 17  is a pictorial view of another breath acetone measurement system according one embodiment, including a side cutaway view of a measurement device that is part of the system, in which the measurement device comprises an integrated heart rate monitor; 
         FIG. 18  is a functional block diagram illustrating the configuration of an embodiment that can be used in conjunction with a nanoparticle-based sensor; 
         FIG. 19  is a schematic representation of an embodiment that utilizes two conditioning devices and a sensing device; 
         FIG. 20  illustrates an embodiment of a hand-held breath gas analyzer with a nanoparticle-based sensing device that embodies the configuration of  FIG. 19 ; 
         FIG. 21  is a graph showing the sensitivity to acetone of a nanoparticle-based sensor as disclosed herein; 
         FIG. 22  is a graph showing the sensitivity to acetone of a nanoparticle-based sensor as disclosed herein; 
         FIG. 23  is a graph showing the sensitivity to acetone of a nanoparticle-based as disclosed herein; 
         FIG. 24  is another graph showing the sensitivity to acetone of a nanoparticle-based sensor as disclosed herein; 
         FIG. 25  is another graph showing the sensitivity to acetone of a nanoparticle-based sensor as disclosed herein; 
         FIG. 26  is another graph showing the sensitivity to oxygen of a nanoparticle-based sensor as disclosed herein; 
         FIG. 27  is another graph showing the sensitivity to isopropanol of a nanoparticle-based sensor as disclosed herein; 
         FIG. 28  is an electrical diagram that shows a typical electrical circuit associated with a nanoparticle-based sensor system used in a breath measurement system; and 
         FIG. 29  is an electrical diagram that shows an electrical circuit associated with a nanoparticle-based sensor system. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to different embodiments and methods 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 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. 
     There are many instances in which it is desirable to sense or measure 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 disclosure. 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. The terms “sense,” “analyze” and “measure,” including their grammatically-based counterparts such as “sensing,” “analysis” and “measurement,” are used broadly and synonymously to mean detecting the presence of one or more analytes, or to measure the amount or concentration of the one or more analytes, or whether the analyte is within a particular concentration range, e.g., at least 1 part per million (“ppm”). 
     Breath acetone measurement devices according to certain embodiments (including the associated communications device described herein below) are designed to be used and operated by a “user” (e.g., a dieting person, athlete, patient, etc.) whose acetone concentrations are being measured. They are amenable to use by the user alone, for example, without the presence or assistance of a friend, aid, nurse or clinical staff, etc. Such devices also are amenable, however, to use by a person other than the “user” whose acetone levels are being measured, for example, such as a coach, trainer, doctor, nurse, clinical technician, family member, friend and the like. Thus, although the “user” is the person whose breath acetone levels are being measured, the “user” may or may not also be the person who performs the manual commands and operations using the device, for example, wherein a patient exhales into a breath bag but a clinician or technician attaches the bag to the device housing and initiates the test. For simplicity and ease of illustration, throughout the detailed description section in this document, the “user” is assumed to be both the person whose breath acetone is being measured and the operator of the measurement device, even though this may not be and need not be the case in a given instance or application of the system. 
     Breath measurement devices according certain embodiments also are designed, sized and configured to be used not only in a clinical setting, (e.g., in a hospital, out-patient clinic, physician&#39;s office, nutritionist&#39;s office, diet treatment center, laboratory, and so on), but also in non-clinical settings, (e.g., the user&#39;s home, office, workplace, gym, while traveling, and so on). They can be “portable” in that they are sufficiently small and light weight that they can be conveniently lifted and carried and used by an individual at various locations. Although hand-held devices are included, this portability also includes table-top configurations and the like, provided they can be lifted and carried by an individual. 
     Acetone is an important analyte in breath measurement, and breath acetone measurement results or data can be extremely useful in managing the health and wellness of the user. Acetone is a member of a class of analytes known as ketones or, similarly, ketone bodies. Ketone bodies as the term is used in biochemistry and physiology means acetoacetate, β-hydroxybutyric acid (β-HBA″), β-hydroxybutyrate (β-HB″) and acetone. Acetone is usually the only ketone body found in breath. Ketone bodies provide a supplementary or substitute form of energy that can be used during various metabolic states including stress, starvation, caloric regulation, or certain pathologies, e.g., such as certain diabetic states, epilepsy and others. Breath acetone levels, for example, often are elevated when any of these metabolic states are encountered. Not uncommonly with diabetic patients, for example, low insulin levels and elevated blood glucose levels result in high concentrations of ketones in the body. This sometimes causes a condition known as diabetic ketoacidosis (“DKA”). 
     Patients in DKA commonly experience symptoms such as nausea, fatigue, and rapid breathing. The patient also emits a distinct fruity odor in the breath, which is 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. 
     In contrast, a condition known as hyperosmolar non-ketotic syndrome is where ketone levels in the body are subnormal, meaning that the body is not producing enough ketone bodies for normal functioning. 
     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, nutrition advisors and the like to adjust weight management plans to individual physiology, lifestyles, user compliance with dietary restrictions, and the like. 
     A hand-held breath acetone analyzer also 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 correspondingly 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 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 needed, including a lancet for blood sampling, test strips, a specialized device and batteries. Several studies show that urine analysis is not accurate. 
     A class of sensors referred to as “nanoparticle-based sensors” offers a potential sensor technology in various breath sensing applications. Nanoparticle-based sensors offer the potential of being sufficiently sensitive and selective for a number of breath sensing systems, while also being relatively reliable and inexpensive. 
     In operation, most nanoparticle-based sensors are most effective, and may only operate effectively, at elevated temperatures of about 150° C. (about 300° F.). They therefore are heated from a power or heat source prior to and as part of their use. For use in portable breath measurement devices, this requires that electrical circuitry and a suitable power source be provided. 
     Many portable breath measurement devices, and apparently nearly all of the relatively few that are commercially available, are designed such that the user positions the breath measurement device in contact with his or her mouth and exhales directly into the device. If such direct-contact devices are to employ a nanoparticle-based sensor, this places the heated sensor in fluid communication with the user&#39;s mouth and respiratory tract. Even though under normal operation the user is instructed only to exhale into the device, if the heat from the sensor is sufficiently substantial, it may be transported to the user&#39;s mouth and possibly his or her respiratory tract, e.g., by radiant transport, where it can cause irritation or personal injury. If the user inadvertently or otherwise inhales during the procedure, he or she may greatly increase that risk of exposure, e.g., by convecting the heat and associated air into his or her mouth and respiratory tract. 
     At elevated temperatures commonly encountered with nanoparticle-based sensors, materials from the sensor material itself, or from the material in the device in the vicinity of the sensor, can vaporize or degas, thereby presenting potentially harmful or toxic materials into the gas stream. These toxic materials also can be inhaled during use of the device, thus entering the user&#39;s mouth and potentially his or her respiratory tract and thereby causing injury. 
     Electrical aspects of the breath measurement devices also pose risks. Electrical anomalies can arise, for example, such as electrostatic discharge, power surges or spikes, overvoltage or overcurrent conditions, radiation, and the like. Such anomalies can present risks through their impact on the device, for example, such as causing aberrant measurement results or damage to the device, and they may pose threats of personal discomfort or injury to the user, such as burns, electrical shock, and the like. 
     System with User-Direct Breath Sample Input 
     The systems and methods described in this disclosure can work in conjunction with software systems and mobile devices, such as the mobile device shown in  FIG. 1 . Exemplary software systems are described, for example, in U.S. Pat. No. 9,341,632, entitled “Ketone Measurement System Capable of Detecting Correlations Between Measurements and User Behaviors,” and U.S. patent application Ser. No. 15/040,790, filed Feb. 10, 2016, entitled “Method and Apparatus for Rapid Quantification of an Analyte in Breath,” the entirety of both of which is hereby incorporated by reference as if fully set forth herein. 
     In some embodiments, a system  10  is provided for measuring acetone in a breath sample of a user and appropriately reporting or storing the measured result or results. 
     System  10  comprises a portable breath measurement device or apparatus  12  and an electronic or communications device  14 . Measurement device  12  is useful for analyzing the breath sample to measure the acetone in it. Electronic or communications device  14  is operatively coupled to the measurement device  12  to selectively receive the measurement result from device  12  and store it, process it, and/or communicate it to another device, such as a remote system, network, central database, a cloud application, and/or the like. Electronic or communications device may comprise, e.g., a computer, laptop, tablet computer, cellular phone, a smart phone and/or the like. Measurement device  12  can be detachably coupled to electronic device  14  in this embodiment, for example, via a universal serial bus (“USB”) or similar adapter cable  16  that allows measurement results data to be transferred from measurement device  12  to electronic device  14 , and for electrical power to be supplied to measurement device  12 , to operate the device or to charge a battery pack  18  that in turn provides operational power to device  12 , or a combination of these. 
     Measurement device  12  comprises a housing  20  that, in this embodiment, includes a tubular or substantially cylindrical body. Housing  20  may be constructed of a rigid material that maintains its stiffness and structural integrity under the operating conditions as described herein, and which can maintain its external temperature in a range so that a user may hold the device without discomfort or injury during its operation. Housing  20  has an upstream end  22  and a downstream end  24 . 
     Housing  20  also comprises a flow path  26  disposed within housing  20 . Flow path  26  comprises an upstream end  28  corresponding to housing upstream end  22  and a downstream end  38  corresponding to housing downstream end  24 . The direction of flow from upstream end  28  to downstream end  30  is referred to herein as the downstream direction  32 . The direction directly opposite to the downstream direction, i.e., from the downstream end  30  to the upstream end  28  is referred to herein as the upstream direction. 
     The system may include a user-direct breath input device (sometimes referred to herein as a conduit) that facilitates the input of the breath sample into the flow channel directly from the respiratory tract of the user, e.g., by exhaling directly into device  12 . The breath input device may comprise any one of a number of devices that is configured to provide the breath sample at the upstream end of the flow path so that the breath sample can be flowed into the flow path. Examples include a mouthpiece, face mask, breathing tube, nasal airway, and/or the like. In direct breath input designs, the system may include a mouthpiece into which the user can directly exhale. A face mask may be useful or in some cases even necessary, for example, if the user is unconscious, has a mouth injury or obstruction, or is otherwise experiencing difficulty with forced expiration through the oral cavity. 
     In system  10 , the breath input device of measurement device  12  comprises a mouthpiece  34  affixed to the proximal or upstream end  22  of housing  20 . (Incidentally, for ease and simplicity of description, and viewing the measurement device from the perspective of the user and the breath sample flow regime during normal use and operation, components and features of measurement device  12  and the other measurement devices described herein are referred to as “proximal” if they are relatively nearer to the upstream end of the housing and the flow path, and they are referred to as “distal” if they are relatively nearer to the downstream end of housing and flow path.) 
     Mouthpiece  34  at its proximal end has an opening  36  for entry of the breath exhaled from the user. The direction of the breath as it is inputted into mouthpiece  34  is shown by the arrows at  38 . Mouthpiece  34  at a distal end  40  is coupled to the substantially cylindrical body of housing  20 . Upstream end  28  of flow path  26  is in fluid communication with the interior or flow channel of mouthpiece  26 . 
     In some systems, the measurement device may include a conditioning device that conditions the breath sample as it is inputted into flow path  26  and prior to its sensing or analyte measurement. The conditioning device may condition the breath sample, for example, for temperature, humidity, flow rate, flow velocity, pressure, concentration, interferents, or some combination thereof. Parameters such as, for example, temperature, pressure, water vapor content, and/or flow rate may significantly impact the ability of chemical sensors to reproducibly sense the concentration of an analyte. 
     Exhaled human breath usually contains a large amount of water vapor, and semiconducting nanoparticles in general are highly sensitive to the moisture content of the gas sample. In detecting analytes at low concentrations, which is the case for breath analysis, water vapor can obscure the response of the sensor to the analyte, either completely destroying the ability of the sensor to measure the analyte of interest or significantly deteriorating its performance. Addressing the moisture level of breath samples is challenging, e.g., 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. If a given sensor technology has significant response 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 at least a portion of 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 breath analytes of interest, including acetone, are attracted to liquid water such that condensation will also affect the amount of analyte that ultimately reaches the detector. 
     A given sensor design also may have an operating range that comprises a specific, bounded range of concentrations at which the sensor operates, or in which it operates optimally, or so that amplification or other adjustment of the analyte concentration is desired. Similarly, the presence of interferents, e.g., certain chemical components other than the target analyte or analytes that interfere with the measurement attributable to the target analyte or analytes, may create obstacles so that it is necessary or desirable to reduce the concentration or presence of one or more of these interferents. 
     The conditioning device may comprise a sorbent trap for reducing the concentration of or removing unwanted interferents. 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 also may consist of or comprise a flow regulation device. Regulation of the flow of the breath sample in the flow path may take a number of forms, including regulation of flow rate, flow velocity, the flow regime (laminar, turbulent, etc.), and/or the like. 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 pre-determined 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. Flow regulation may comprise one or more flow diffusers to diffuse or mix the flow. 
     The conditioning device also may be or comprise a device for adjusting or controlling the temperature of the breath sample at various locations within the flow path. This may comprise, e.g., a heater, a cooler, or some combination of these. Temperature control or adjustment also may be achieved by controlling flow characteristics, e.g., by using a narrow orifice to rapidly increase flow velocity while reducing flow rate and pressure, such as in an evaporator. 
     The conditioning device may be disposable. In certain embodiments, it may be desirable to package the conditioning device in a sterile package. Accordingly, the measurement device may comprise an access that permits the conditioning device to be inserted, removed, and either replaced or replenished. 
     Conditioning devices that may be suitable for use are disclosed in the present assignee&#39;s U.S. Pub. No. 2014/0276100, the entirety of which is hereby incorporated by reference as if fully set forth herein. 
     In system  10 , measurement device  12  may include a conditioning device in the form of a humidity extraction device or desiccant  42 . The humidity extraction device  42  may include a substantially cylindrical container in fluid communication with, for example disposed within, flow path  26 , adjacent to, in series with and immediately downstream with respect to mouthpiece  34 . The container can be filled with a desiccant material which may consist of 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 (P 2 O 5 ), zeolite, silica gel, aluminum oxide (Al 2 O 3 ), or molecular sieve. In conditioning device  42 , the desiccant material comprises, and may consist essentially of, calcium dichloride with a particle size range of −12+18 mesh. The perimeter of each of the proximal and distal ends of desiccant  42  can be covered with a seal ( 44  and  46 , respectively), such as an elastomeric material such as rubber or a resilient plastic, to prevent the passage of the breath sample in the annular space between the outer cylindrical surface of desiccant  42  and the corresponding interior of housing  22  that contains desiccant  42 . Because mouthpiece  34  can be detachable, as further described herein below, conditioning device  42  can be removed and replaced or replenished. 
     Measurement device  12  may include a nanoparticle-based sensor subsystem  50  comprising a sensor  52  disposed in housing  20  and in fluid communication with, for example within, flow path  26  (see  FIG. 2 ). Sensor  52  can be disposed at an intermediate location between upstream end  28  and downstream end  30  of flow path  26 , just downstream of desiccant  42 . 
     Nanoparticle-based sensors are comprised of a nanomaterial coupled to an electrode. The term “nanomaterial” is used herein broadly according to its common meaning in the field, to include an analyte-responsive material or element that has been synthesized so that the majority of individual particles or fundamental units of the material or element have characteristic dimensions (e.g., spherical diameter for spheres, cross-sectional diameter for nanotubes, etc.) within the range of a few nanometers to several tens of nanometers, and have been deposited onto a substrate (e.g., as thick-films, self-assembled lawns, etc.). The term “nanomaterial” as used herein also may include substances whose individual particle dimensions are outside of the “nano” specification noted above, but which nevertheless are 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 (Fe 2 O 3 ), tungsten (VI) oxide (WO 3 ), titanium (IV) oxide (TiO 2 ), molybdenum (VI) oxide (MoO 3 ), vanadium (V) oxide (V 2 O 5 ), chromium (III) oxide (Cr 2 O 3 ), indium (III) oxide (In 2 O 3 ), tin (IV) oxide (SnO 2 ), manganese (IV) oxide (MnO 2 )), 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 Fe 2 O 3  doped with TiO 2 , 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.). 
     Nanoparticle-based sensors typically 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. The nanoparticle-based sensor may be disposable or it may be reused, depending on the application. 
     The substrate may be any material that 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, and which is otherwise suitable for the application, e.g., by being substantially free of any electrical or magnetic properties that would interfere with the desired operation of the sensor, that do not degas or sublimate interferents, etc. Suitable substrates may include ceramics such as alumina (Al 2 O 3 ), glass, or thermally-stable plastics such as polyimide. Nanoparticle pastes can be applied onto substrates with suitable temperature resistance and mechanical rigidity. 
     An enlarged top or plan view of sensor subsystem  50  is shown in  FIG. 2 , and an enlarged bottom view is shown in  FIG. 3 . Sensor subsystem  50  comprises a sensor  52  which in turn comprises a sensor pad  52   a  which in turn comprises a nanomaterial  52   b  disposed on a substrate  52   c . In system  10  and more specifically in measurement device  12 , nanoparticle-based sensor  52  comprises a tin oxide semiconductor sensor formed on an alumina substrate, for example, such as a TGS 822 sensor, commercially available from Figaro USA, Inc. of Arlington Heights, Ill. Alternatively, the sensor may utilize γ-ferric oxide, antimony salt and platinum, such as that disclosed in PCT application IN13/000120 entitled: “A Sensor Composition for Acetone Detection in Breath,” which is hereby incorporated by reference in its entirety herein. 
     Sensor pad  52   a  is disposed on a printed circuit board (“PCB”)  58 . A pair of electrode contacts  60   a  and  60   b  are disposed on and in ohmic contact with respective ends of sensor pad  52  and, more specifically, with nanoparticle material  54 . A corresponding pair of electrical leads  62   a  and  62   b  extend from contacts  60   a  and  60   b  across sensor PCB  58  and to an edge connector  64 . 
     Operating temperature ranges for nanoparticle-based sensors are commonly in the 100-500° C. range, but can be outside of this range in more rare circumstances. Many operate most optimally in the range of about 300° C. to 400° C. Accordingly, it may be necessary to provide a heating device to raise the sensor to the required temperature during measurement. Thus, sensor subsystem  50  may include a heating device  66  that in turn comprises a resistive coil or element  68  disposed adjacent to nanoparticle material  52   b  on sensor pad  52   a  and a pair of electrodes  70   a  and  70   b  coupled to resistive element  68 . Electrodes  70   a  and  b  also are coupled to edge connector  64 . 
     As an alternative to or in addition to heating device  66 , which is disposed on the top side of PCB  58 , a heating device  72  may be disposed on the bottom side of PCB  58 , proximate to and/or under sensor pad  52   a  (see  FIG. 3 ). In measurement device  12 , both are provided. As with heating device  66 , heating device  72  comprises a resistive coil or element  74  disposed adjacent to or under sensor pad  52   a  and a pair of electrodes  76   a  and  76   b  coupled to resistive element  74 . Electrodes  76   a  and  b  also are coupled to edge connector  64 . 
     The electrode contacts  60   a,b  and electrodes  62   a,b ,  70   a,b  and  76   a,b  can be screen printed onto the substrate  52   c  and surface material of PCB  58 , respectively. A nanomaterial paste can then be applied over substrate  52   c  and cured at high temperatures. A resistance temperature detector trace also can be screen printed onto substrate  52   c , allowing closed loop control of the sensing element&#39;s temperature under varying conditions. 
     The electrode contacts and electrodes 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. They may have a smooth surface or, for certain applications, it may be designed to have a rough surface. As regards the electrode contacts  60   a,b , such roughness could allow for increased surface area of the nanoparticle sensing material. The electrode leads at edge connector  64  are spaced so that a single 6-position compression conductor makes contact to both the top and bottom sides simultaneously. 
     Resistive heating elements  68  and  74  can be deposited onto the respective electrodes near the sensor 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  68  and  74  can be comprised of any number of materials that 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 others. The heater or heaters 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 subsystem may include a temperature sensor  54  and temperature control element located close to the nanoparticle sensor  52  and may comprise resistive heating wires or traces, resistance temperature devices, thermocouples, control circuitry, and/or other thermal control devices. 
     The nanomaterial  52   b  coupled to the electrode  62  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 subsystem may comprise 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. 
     As shown in  FIGS. 1-3 , a cable run  78  comprising wires or electrical conductors for each of the electrodes running to edge connector  64  can run from connector  64  to a device printed circuit board  80  disposed at the distal end of housing  20 . PCB  80  comprises the processing and gating circuitry to cause heating devices  66  and  72 . 
     Both PCB  80  and nanoparticle-based sensor  50  can be ohmicly coupled to electronic device  14  and/or battery pack  18 , so that they can receive power for their operations. 
     In normal operation of system  10 , upon being powered up, PCB  80  causes heating devices  66  and  72  to heat nanoparticle-based sensor  50  to its optimal operating temperature, which may be about 400° C. This heating process also removes some of the humidity and possibly other adsorbed gases or materials on sensor  52 . Once sensor  52  reaches this temperature, as indicated by temperature sensor  54 , an indicator is provided to user, such as a light (not shown) indicating that the device is ready to begin the acetone measurement test. The user then exhales into mouthpiece  34 , which causes the exhaled breath sample to enter flow path  26  and flow in it in downstream direction  32 . As the sample passes through desiccant  42 , moisture in the sample is substantially reduced. As the sample exits desiccant  42  and continues down the flow path, it contacts sensor  52  at the intermediate location, whereupon the acetone in the breath sample interacts with the sensor and the sensor generates a measurement signal that is representative of the concentration of the acetone in the breath sample. This measurement signal is passed via electrodes  62   a  and  b  and cable  78  to PCB  80 , which then communicates the measurement signal to electronic device  14 . 
     In a modification of this embodiment, USB cable  16  can be replaced with a wireless link between measurement device  12 , and more specifically PCB  80 , and electronic device  14 . After the breath sample passes sensor  52  and proceeds down flow path  26  in downstream direction  32 , past a one-way exit valve  82 , and it is vented at a series of venting ports  84  at the distal or downstream end of flow path  26 . Venting ports  84  are angled with respect to the longitudinal axis of housing  20  and with respect to the plane normal to the longitudinal axis L, as indicated at  86 , so that the warmed breath sample is vented away from the user. A grip  88  is disposed on the exterior of housing  20  in the vicinity of the intermediate location so that the user can grip measurement device  12  at a location that is insulated from sensor  50  and is away from the vented breath sample. 
     With system  10  as thus far described, there is a concern that sensor  52 , and the heat associated with it during operation, is in fluid communication with the user&#39;s mouth, possibly nasal passages, and respiratory tract via the portion of flow path  26  that is upstream of sensor  52  (chamber  26   a ) and through mouthpiece  34 . Thus, if the user were to inadvertently inhale during the normal use of system  10 , discomfort and potentially personal injury could occur. To address such concerns, system  10  may include a flow control subsystem to mitigate or prevent respiratory tract inhalation. 
     The flow control device or subsystem can be disposed in the housing and in the flow path between the upstream end and the nanoparticle-based sensor at the intermediate location. It prevents flow of the breath sample in an upstream direction opposite the downstream direction. 
     The flow control device or subsystem of system  10  comprises a one-way valve  90  disposed in flow path  26  at the distal end of mouthpiece  34  and upstream from desiccant  42 . Optionally, the flow control subsystem may include a second one-way valve  92  disposed in flow path  26  downstream from conditioning device  42  but upstream from the intermediate location and sensor  52 . Both valves  90  and  92  allow the breath sample to flow in the downstream direction  32 , but close to prohibit the breath sample from flowing back in the upstream direction. First one-way valve  90  further mitigates the risk of the user inadvertently inhaling the desiccant in conditioning device  42  in the event of a failure of the latter in which desiccant is released. 
       FIGS. 4A  and B provide enlarged and partial cutaway side views of the upstream section of housing  20  in which valves  90  and  92  are disposed.  FIG. 4A  is an exploded view expanded along the longitudinal axis L of housing  20 .  FIG. 4B  shows a corresponding side view, but in which the sections have been moved back together longitudinally to their mated and operational configurations. 
       FIG. 4A  shows mouthpiece  34  longitudinally separated from housing  20  in expanded or exploded form. Conditioning device  42  is shown positioned between mouthpiece  34  and housing  20 . One-way valve  90  is disposed in mouthpiece  34  upstream from conditioning device  42 . Mouthpiece  34  has a breath input section  34   a  at its proximal region and a skirt section or skirt  34   b  at its distal region. The mouth piece  34  can have a distal edge  34   c  and a distal opening  34   d . A stop flange  34   e  can be fixedly disposed peripherally in the interior of mouthpiece skirt  34   b  to serve as a stop for conditioning device  42 , to secure and immobilize device  42  in the mouthpiece and prevent it from moving upstream past stop flange  34   e.    
     Housing  20  can have an upstream or proximal skirt portion  20   a , a proximal edge  20   b  and a proximal opening  20   c . A stop flange  20   d  can be fixedly disposed peripherally in the interior of proximal skirt  20   a  to serve as a downstream stop for conditioning device  42 , to secure and immobilize device  42  in proximal skirt  20   a  of housing  20  and prevent it from moving downstream past stop flange  20   d.    
     One-way valves  90  and  92  differ in their location within measurement device, but the valves themselves have identical construction.  FIG. 5  shows a longitudinal cutaway view of each valve as indicated by line  5 - 5  in  FIG. 4A . Each valve  90 , 92  can include a peripheral flange  94  that can be fixedly disposed peripherally in the interior of the flow path  26 , which for valve  90  is the interior of mouthpiece skirt  34   b  and for valve  92  is the interior of proximal skirt  20   a . Peripheral flange  94  can be spaced from the corresponding stop flange  20   d  and  34   e  so that a small air gap is provided between conditioning device  42  and the corresponding peripheral flange. Peripheral flange  94  can include a shelf  94   a  that extends into flow path  26  perpendicularly with respect to the longitudinal axis L. A support beam  96  can extend at least partially laterally across peripheral flange  94 . A post  98  can extend longitudinally from the center of support beam  96  at the center of peripheral flange  94  and at the longitudinal axis L. One or more support members  100  can extend from peripheral flange  94  inward radially so that they are coplanar with respect to shelf  94   a . A substantially circular semi-rigid valve closure  102  can be disposed on the substantially planar support structure formed peripheral flange  94  (and more specifically shelf  94   a ), support beam  96  and support members  100 . Valve closure  102  has a hole  102   a  at its center to receive post  98 , so that valve closure lies at the base of post  98  and against the support structure. The relative sizing of hole  102   a  and post  98 , together with appropriate beveling or tapering of post  98 , secure it in this position with a press-fit-type lock. The diameter of valve closure  102  is substantially the same as but slightly less that the interior diameter of flow path  26 , and is greater than the diameter of the interior periphery of support shelf  94   a . Thus, valve closure  102  at rest conforms to the plane of the support structure and rests at its periphery  102   b  on shelf  94   a  and thereby closes flow path  26  at that point or location. 
     Valve closure  102  may comprise any one of a range of materials that is sufficiently rigid to prevent backflows of air, but yet sufficiently resilient to permit air flows in operation as further described herein below. Valve closure also should have sufficient thermal stability to retain its semi-rigidity under thermal conditions encountered operationally. It also should have appropriate biocompatibility for the circumstances of its intended use. In some embodiments, valve closure  102  is a thin polyethylene sheet. 
     The operation of the valve ( 90 , 92 ) is illustrated in  FIGS. 6A and 6B , wherein  FIG. 6A  shows a side cutaway view of the valve in a closed state, and  FIG. 6B  shows a side cutaway view of the valve in an open state. In  FIG. 6A , the valve is at rest, e.g., in storage or prior to use. Valve closure  102  conforms to the plane of the support structure and rests at its periphery  102   b  on shelf  94   a  so that flow path  26  is closed at that point or location. When the user exhales into mouthpiece  34  (or, with respect to other embodiments as described herein below, the breath sample is otherwise inputted into the flow path), as shown by arrows  38 , the breath sample flows in the downstream direction  32 . The pressure from this inputted fluid sample is applied to valve closure  102 , which at its attachment point at post  98  has no effect with regard to motion. At its peripheral edge  102   b , however, which is unattached to the support structure or, more specifically, to shelf  94   a , and is free to move in downstream direction  32 , peripheral edge  102   b  moves away from shelf  94   a , thereby creating a flow passage channel around valve closure  102  and thus opening flow path  26  to allow this downstream flow (see  FIG. 6B ). 
     If the user happens to inhale during operation of the device  12  and, most disconcertedly, when sensor  50  is at its elevated operating temperature or higher, this upstream flow would quickly create a low pressure condition at the upstream side of valve closure  102 , thereby causing a force  106  in the upstream direction that would close valve closure  102  and prevent further upstream flow (see  FIG. 6A ). Ideally, this volume of fluid that is allowed to backflow in the upstream direction prior to and as part of closing valve closure would include only a small volume of fluid that is sufficiently small, close to valve closure  102  and far from sensor  50 , that no more than minimal and safe heat transfer takes place. This can be accommodated through such specific design features in a given application as the sizes of the flow path and valve closure, the spacing from the sensor to the valve closure, and the speed of valve closure. 
     In system  10  as described and illustrated herein, because measurement device  12  may include not only valve  90  at mouthpiece  34  but also valve  92  downstream of conditioning device  42 , such unintentional upstream or backflow would close both valves  90  and  92  substantially simultaneously. As a result, the relatively minimal portion of the fluid from the portion of the flow path in which the sensor resides that moves past valve  92  and into conditioning device  42  as valve  92  is closed would be insufficient to travel upstream through conditioning device  42  and through valve  90  and into the mouthpiece before valve  90  is closed. The sizing of conditioning device along longitudinal axis L the spacing between valves  90  and  92 , or both, could be used to guarantee this result. 
     Alternative designs for the one-way valves  90 , 92  may be used. As an example, a “butterfly” valve  110  is shown in  FIG. 7 , which more specifically shows a longitudinal end view of valve  110  looking down flow path  26  assuming a pair of valves  110  is substituted for valve pair  90  and  92 . The support structure for valve  110  is the same as for valves  90  and  92 , more specifically including peripheral flange  94 , shelf  94   a , support beam  96  and support members  100 . Valve  110  does not include post  98  from valves  90  and  92 , but instead comprises a hinge  112  at the top of support beam  96  that is formed by a top bar  114  and a pair of press-on posts  116 . Valve  110  includes a valve closure that is identical to valve closure  102 , but which includes two holes for press-on posts  116  rather than center hole  102   a . When at rest, valve closure rests against shelf  94   a  as shown in  FIG. 6A . The rigidity of valve closure  102  provides a mild bias of peripheral edge  102   b  so that flow path  26  is closed at the location of the valve. When a breath sample is introduced via mouthpiece  34 , as shown at  38 , the hinged valve closure  102  opens with respect to the hinge so that the breath sample is allowed to pass around peripheral edges  102   b  and through the apertures  118  thereby created (see  FIG. 8 ). 
     Another alternative design for the one-way valves  90 , 92 , this one a “ball valve” valve  120  is shown in  FIGS. 9A and 9B .  FIGS. 9A and 9B  show a side cutaway view of the locations in flow path  26  that include valves  90  and  92 , but wherein ball valve  120  is substituted for valve  90  and, separately, valve  92 .  FIG. 9A  shows valve  120  in a closed state, and  FIG. 9B  shows the valve  120  in an open state. Valve  120  comprises a ball  122  disposed in a cylindrical ball housing  124  that includes a biasing device  126  such as a biasing spring that biases ball  122  into a hole  128  in a concave wall  130  of mouthpiece breath input portion  34   a . Hole  128  is smaller than the diameter of ball  122 , so that ball  128  when thus biased blocks hole  128  and closes flow path  26 . 
     When a breath sample is inputted into mouthpiece  34  as indicated at  38 , the pressure created in breath input portion  34   a  pushes ball  122  longitudinally downstream against biasing spring  126  in housing  124 , thus opening hole  128  so that the breath sample can flow through valve  120 , as shown at  132 . When the input of breath sample ceases, the pressure in mouthpiece input portion  34   a  drops, and biasing spring  126  forces ball  122  upstream in housing  124  to re-close hole  128 . 
     Returning to measurement device  12  as shown in  FIG. 4 , mouthpiece  34  can be detachable from housing  20 . In other configurations, the mouthpiece may be fixedly attached to the housing  20 . These components are shown in separate, exploded or expanded view in  FIG. 4A , but they may be assembled into normal form for use as illustrated by the transition from  FIG. 4A  to  FIG. 4B , as will now be described. 
     A user may be provided with at least two components (e.g., two, three, more). One is mouthpiece  34 , with valve  90  permanently or removably affixed in it. Optionally, conditioning unit  42  may come predisposed in mouthpiece  34 , which would be inserted into mouthpiece distal opening  34   d  so that rubber seal  44  contacts and abuts stop flange  34   e . Alternatively, the conditioning device  42  my come predisposed in housing  20 , or as a separate (third) component in addition to mouthpiece  34  and housing  20 . In the continuing description, it will be assumed that conditioning device comes as a pre-disposed and pre-assembled component of mouthpiece  34 . Incidentally, given the personal nature of mouthpiece  34  with respect to a given user and the fact that mouthpiece  34  and conditioning device  42  will become soiled or contaminated with breath components with use, these two components generally will be replaceable or consumable and disposable components of the overall device  12 . 
     Housing  20  can come with one-way valve  92  pre-disposed in its interior as depicted in the drawing figures. The outer diameter of housing proximal skirt  20   a  is slightly smaller than the inner diameter of mouthpiece skirt  34   b , and they are sized relative to one another so that housing proximal skirt  20   a  can be slid into and surrounded by mouthpiece skirt  34   b  in substantially air-tight, slip-fit arrangement (or press-fit, snap fit, threaded, or any other air-tight arrangement). Alternatively, the housing proximal skirt  20   a  can be slide over the mouthpiece skirt  34   b  in the substantially air-tight arrangement. As mouthpiece  34  is slid over housing proximal skirt  20   a , the distal or downstream end of conditioning device  42  is slid into housing proximal opening  20   c  until reaches its final position in the housing, e.g., when rubber seal  46  contacts and abuts stop flange  20   d . As this occurs, mouthpiece  34  is in substantially airtight, mating contact with housing  20  at the latter&#39;s proximal end, so that device  12  is as depicted in  FIG. 1 , and conditioning device  42  is fixed and immobilized, for example between stop flanges  20   d  and  34   e . Rubber seals  44  and  46  in abutting arrangement with those flanges can create a substantially airtight section of flow path  26 . 
     The operation of system  10 , fully configured as has been described and illustrated herein, is as follows. With reference to  FIG. 1 , measurement device  12  can be coupled to electronic device  14  via cable  16  and the device is powered on. An indicator may indicate when the heating devices have raised the temperature of sensor  52  to its optimal operating temperature, for example, a light on the housing can be illuminated. This can indicate to the user that the device is ready for the acetone test. Upon receiving this indication, the user places his or her mouth on mouthpiece  34  and exhales to input a breath sample into device  12  through the mouthpiece, as indicated at  38 , and in downstream direction  32 . This downstream flow causes one or more one-way valves  90  and  92  to open so that the breath sample optionally flows through conditioning device  42 , where the humidity in the sample is reduced, and into chamber  26   a  where sensor  52  is located. The dehydrated or otherwise conditioned breath sample contacts sensor  52 , which is still at its optimal operating temperature, whereupon sensor  52  interacts with or measures the breath sample and generates a measurement signal. That measurement signal can be communicated via cables  78  to device PCB  80 , which then communicates the signal to electronic device  14 . 
     If during the exhalation or otherwise during the operation of device  12  the user inhales or otherwise causes a back pressure or back flow at mouthpiece, the one or more one-way valves  90  and  92  promptly will be closed, thus preventing any gas or heat from sensor  52 , or chamber  26   a , from reaching mouthpiece breath input section  34   a , and thereby preventing such gas or heat from reaching the mouth or respiratory tract of the user. 
     System with Breath Bag 
     In accordance with another aspect of the present disclosure,  FIGS. 10-12  illustrate a system  210  for measuring acetone in a breath sample of a user and appropriately reporting or storing the measured result or results. System  210  is very similar to system  10 , including many of the same components. Accordingly, numerals used to identify features of the system  210  are incremented by a factor of two hundred (200) to identify like features of the system  10 . 
     System  210  comprises a portable, hand-held breath measurement device  212  and an electronic or communications device  214 , the latter of which here is illustrated as a cellular telephone in the form of a so-called “smart phone,” such as an Apple iPhone®. Measurement device  212  is wirelessly coupled to electronic device  214  in this embodiment, for example, via a WiFi or Bluetooth module  281  that allows measurement results data to be transferred from measurement device  212  to electronic device  214 . Electrical power can be provided within measurement device  212  a battery pack  218  as described herein above with respect to system  10 . 
     Measurement device  212  comprises a housing  220  that, in this embodiment as in system  10 , comprises a tubular or substantially cylindrical body. To better illustrate measurement device  212 , as in device  12 , housing  220  is disposed about a longitudinal axis L that corresponds to the axis of the cylindrical body. Housing  220  can be constructed of materials as described herein above. Housing  220  also has an upstream end  222  and a downstream end  224 . 
     Housing  220  further comprises a flow path  226  disposed within housing  220  substantially along longitudinal axis L. At least a part of flow path  226  comprises tubing, although sections of it may not, as further described herein below. Flow path  226  comprises an upstream end  228  corresponding to housing upstream end  222  and a downstream end  238  corresponding to housing downstream end  224 . The direction of flow from upstream end  228  to downstream end  230  is referred to herein as the downstream direction  232 . The direction directly opposite to the downstream direction, i.e., from the downstream end  230  to the upstream end  228  is referred to herein as the upstream direction. 
     An input coupler  226   b  (sometimes referred to herein as a conduit) can be provided at upstream end  228  of flow path  226 . The input coupler  226   b  may be substantially cylindrical. At least one post  226   c  can be disposed (e.g., fixedly disposed) within the interior of input coupler  226   a.    
     System  210  can also include a breath input device to facilitate the input of the breath sample into the flow channel. In system  210 , an “indirect” breath input device can be used, as well as devices that involve indirect input of the breath sample, such as a sealed breath sample storage container or unit, e.g., a tank, bottle, syringe, breath sample collection bag, or combinations of these, and the like. In indirect input designs, the breath sample storage unit may be fluidically coupled to the flow path using a conduit such as a pipe, tubing, and the like. 
     In system  210 , the breath input device comprises a breath bag  234 . Breath bag  234  is used by the system user separately from measurement device  212  to collect and retain a breath sample. Breath bag  234  then can be coupled to measurement device  212  to provide the breath sample to flow path  226  for analysis. In some configurations, once the measurement is made, breath bag  234  can be detached from measurement device  212  and re-used or discarded. 
     Breath bag  234  comprises a bag portion  234   a , a mouthpiece, and a connector, such as ferrule  234   b . Breath bag portion  234   a  contains and retains the breath sample inputted by the user. The wall materials of breath bag  234  are substantially air tight, substantially impermeable to acetone. The wall materials of the breath bag  234  may be substantially impermeable to both ambient air components outside the bag and chemical interferents within the collected sample. The walls of the breath bag may be any of a variety of materials that is sufficiently impermeable to air or breath and the analyte of interest, which here is acetone. The wall material also should be substantially impermeable to unwanted constituents of the air or gas outside the bag from infiltrating into the breath sample. Optionally, the material may be relatively light weight for ease of portability and use, and have sufficient flexibility or resiliency to collapse or fold neatly for storage. Examples of such materials comprise low density polyethylene, linear low density polyethylene, polyester films such biaxially-oriented polyethylene terephthalate, and such related commercially-available materials, such as Mylar, Tedlar, Melinex and Hostaphan. In some embodiments, the bag portion material is a low density polyethylene. 
     Mouthpiece and ferrule  234   b  serves several functions. Initially it can serve as a mouthpiece for collection of the breath sample from the user, although the bag  234  may have a mouthpiece separate from the ferrule  234   b . In that regard, the ferrule  234   b  may include a one-way valve  290  (e.g., identical to one-way valve  90  of measurement device  12  as described herein above and as shown in  FIGS. 5 and 6 ), but wherein the valve can oriented so that the breath sample is permitted to enter bag  234  but not to exit the bag, except in conjunction with measurement device  212  as described herein below. Ferrule  234   b  can retain or store the breath sample from the time it is collected and until it is used for acetone measurement, as described herein below. 
     Breath bag  234  couples to measurement device input coupler  226   b . In some configurations, the breath bag  234  may also be detachable for reuse or replacement. The manner of this coupling is shown in greater detail in  FIGS. 11A and 11B .  FIG. 11A  shows the breath bag ferrule  234   b  and measurement device input coupler  226   a  in separate but juxtaposed position just prior to coupling. Valve closure  102   b  is in its closed state, and thus coplanar with and supported by the support structure comprising peripheral flange shelf  94   a , support beam  98  and support members  100 , (see  FIGS. 5 and 6A ). This configuration secures the breath sample within bag  234 . 
     Ferrule  234   b  at its distal end (away from breath bag portion  234   a  and toward measurement device  212 ) comprises a ferrule skirt  234   c  that extends distally with respect to valve  290 . Measurement device input coupler  226   a  similarly has a coupler skirt  226   d  that extends outwardly (away from flow path  226  and toward breath bag  234 ). In the process of coupling breath bag  234  to measurement device  212  at input coupler  226   b , one slides ferrule  234   b , and more specifically ferrule skirt  234   c , longitudinally over or within coupler skirt  226   d . As shown in  FIG. 11B , when engaged, the peripheral edge  226   e  of coupler skirt  226   d  can contact and abut the support structure of ferrule valve  290  (peripheral flange  94 , support beam  96 , and/or support members  100 , see  FIGS. 5 and 6A . The exterior of coupler skirt  226   d  is sized to be substantially the same diameter as but slightly smaller than the interior diameter of ferrule skirt  234   c  or slightly larger than the outer diameter of ferrule skirt  234   c , so that the two slidingly engage to form a substantially air-tight seal between the interior of bag portion  234   a  and measurement device flow path  226 . 
     As ferrule  234   b  and input coupler  226   b  are slidingly engaged, posts  226   c  extend through the spaces above and below support beam  96  of valve  290  and contact valve closure  102 , which moves the top and bottom portions of valve closure  102  away from the support structure to open the valve and allow flow of the breath sample from bag portion  234   a  into a breath input portion  226   e  of input coupler  226   b  and into flow path  226 . (See  FIG. 6B .) 
     Alternative designs for the breath collection bag may be used in place of breath bag  234 . Examples include the breath bags and associated flow control hardware disclosed in the present assignee&#39;s U.S. Pub. No. 2014/0276100, and particularly those of  FIGS. 2, 3 and 10 , and associated text in that document, which is hereby incorporated in its entirety herein. 
     Returning to  FIG. 10  and with attention directed to the upstream end of flow path  226  at input coupler  226   b , a pump  241  can be disposed in the flow path downstream from input coupler  22   b . Pump  241  can be configured to pump the breath sample in flow path  226  in the downstream direction  238 . 
     A conditioning device  242  as described herein above with respect to device  42  can be disposed in flow path  226  downstream from pump  241  to receive the output from pump  241 . Rubber seals  244  and  246  can be provided at the upstream and downstream ends, respectively, of conditioning device  242  to prevent unwanted annular flow of the breath sample between conditioning device  232  and the interior wall of housing  220 . A flow diffuser  243  can be provided at the upstream end of conditioning device  242  to diffuse and disperse the breath sample flow across the face of conditioning device  242 , e.g., to avoid channeling within the conditioning device and to improve its efficiency. A flow restrictor, such as a porous metal flow restrictor, can be disposed in the flow path just downstream of pump  241 . 
     Housing  220  in this embodiment comprises two detachable sections, e.g., an upstream housing section  220   a  and a downstream housing section  220   b , which are detachably joined at a joinder  220   c . Although, in other configurations, the housing  220  may include a single section or more than two sections. An enlarged and expanded cutaway view of this joinder area is shown in  FIG. 12 , as indicated by the arrows  12  in  FIG. 10 . The distal or downstream end of upstream housing section  220   a  comprises a skirt  220   d  with a peripheral edge  220   e , which form an opening  220   f . The proximal or upstream end of downstream housing section  220   b , which is configured to slidingly mate with upstream section  220   a , comprises a skirt  220   g . Skirt  220   g  is sized to that its exterior diameter is substantially the same as the interior diameter of upstream housing section skirt  220   d , and slightly smaller, so that skirt  220   g  can be slidingly engaged inside skirt  220   d  to form a substantially air tight seal. A rubber seal  220   h , such as a gasket or o-ring, can be disposed on the upstream end  220   i  of downstream section  220   b , surrounding flow path  226 , so that, as housing sections  220   a  and  b  are slidingly joined, rubber seal  220   h  contacts, joins and seals the flow path in both sections, thus enabling the breath sample to flow through the joinder without leaking breath out of the flow path and without infiltration of air or gas into the flow path at that point. Housing sections  220   a  and  b  can be joined to form an air-tight arrangement (e.g., press-fit, snap-fit, screw-fit, or otherwise). In some configurations, when joined, the housing sections  220   a  and  b  can be secured by a screw  220   j  that extends through upstream housing skirt  220   c  and into downstream housing skirt  220   g.    
     Measurement device  212  further comprises a nanoparticle-based sensor system  250  comprising a sensor  252  disposed in housing  220  and in fluid communication with, for example within, flow path  226 . Sensor  252  can be disposed at an intermediate location between upstream end  228  and downstream end  230  of flow path  226 , for example downstream of conditioning device  242  and joinder  220   c . Nanoparticle-based sensor subsystem  250  and its associated electrical components are as described herein above with respect to nanoparticle-based sensor subsystem  50  and as illustrated in  FIGS. 2-3 . 
     Cables  278  (equivalent to cables  78  in device  10 ) extend down device  212  and ohmically couple nanoparticle sensor  252  with device printed circuit board  280  (equivalent to PCB  80  of device  10 ). Both PCB  280  and nanoparticle-based sensor  252  are ohmicly coupled to battery pack  218  so that they can receive power for their operations. 
     The operation or use of system  210  involves two steps. In a first, the user employs breath bag  234  to collect a breath sample and attaches the breath bag to measurement device  212 . In a second, measurement device  212  inputs the breath sample from breath bag  234 , analyzes it to obtain a measurement result, and outputs that result to electronic device (here iPhone)  214 . 
     In the first step, or breath sample collection step, breath bag  234  is used separately and may be detached from measurement device  212  to collect the breath sample. The user grips the bag by mouthpiece/ferrule  234   b , positions at his or her mouth, and exhales through mouthpiece  234   b  and valve  290  to fill bag portion  234   a  with the breath sample. As this occurs and thereafter, valve  290  prevents the breath sample from escaping from bag portion  234   a  and retains it there. 
     The user then positions breath bag as shown in  FIG. 10  so that mouthpiece/ferrule  234   b  is in alignment with longitudinal axis L and input coupler  226   b  of measurement device  212 , and slides ferrule  234   b  onto coupler  226   b  so that the former is abutted to the latter and posts  226   c  contact and open the valve closure of valve  290 . This allows the breath sample in breath bag  234  to flow into the portion of flow path  226  between breath bag  234  and pump  241 , and to reach equilibrium pressure within this section. It should be noted that this feature may automatically opening the breath bag and allow the breath sample to enter the flow path without the requirement for the user to manually open a valve on the breath bag provides a number of advantages, e.g., such as ease of use, fewer mechanical parts, less risk of disturbing or compromising the seal, and so on. 
     The user then powers up measurement device  212 , whereupon PCB  281  causes heating devices  66  and  72  ( FIGS. 2-3 ) to heat nanoparticle-based sensor  252  to its optimal operating temperature of about 400° C. Once sensor  252  reaches this operating temperature, PCB  280  causes pump  241  to actuate, which causes the breath sample to flow downstream through pump  241 , through conditioning device  242 , through joinder  220   c  and into chamber  226   a . As the breath sample enters chamber  226   a , it contacts nanoparticle-based sensor  252 , whereupon acetone in the breath sample interacts with sensor  252  to generate the measurement signal. The breath sample passes sensor  252  and exits device  212 , such as through exit valve  82  and through venting ports  284 . The measurement signal generated by sensor  252  is communicated via cables  278  to PCB  280 . The measurement signal is then wirelessly communicated via Bluetooth module  281  to electronic device  214 . 
     In view of the foregoing, it is clear that the use of system  210 , which includes detachable breath bag  234 , prevents the risk that heated, toxic or potentially injurious gases from sensor  252  or chamber  226   a  will come into contact with the user&#39;s mouth, oral cavity or respiratory tract. 
     As an alternative or additional safety feature, in systems such as systems  10  and  210 , the nanoparticle-based sensor can be disposed within the housing and the intermediate location can be selected so that the nanoparticle-based sensor is substantially inaccessible to the user during use of the device or system. As shown in  FIGS. 1 and 10 , nanoparticle-based sensor  52  and  252 , respectively, are disposed within their respective housing, where the user cannot intentionally or inadvertently touch or grip them and sustain a thermal or chemical burn. In system  210 , although housing  220  is segmented into an upstream section  220   a  and a downstream section  220   b , they are mated to prevent direct access by the user, and they are secured by screw  220   i . Nanoparticle sensor  250  thus is inaccessible to the user during normal use of measurement device  212 , even though it can be accessed when not in use with the aid of a tool, in this case a screw driver. This segmented design thus affords the opportunity to service or replace the sensor  252  if and when needed, but safely secures it out of the intended or unintended contact by the user during use. 
     It should be noted that the use of a controllable pump in fluidic communication with the nanoparticle-based sensor, e.g., as shown in  FIG. 10 , can allow the user to adjust or control and improve performance characteristics of the device, for example, by controlling such parameters as pump speed, flow rate and pumping time, which can correspondingly affect the temperature of the sensor, the fluid flow characteristics (e.g., turbulence at the sensor), and the like. Given the fact that the sensitivity of many nanoparticle-based sensors are temperature dependent, such features can permit the analyte sensitivity range to be improved without sacrificing precision. 
     System with Sensor on Detachable Insertion Member 
     A system  310  according to another embodiment is shown in  FIG. 13 . System  310  is very similar to system  10 , including many of the same components, including one-way valves  90  and  92 . Accordingly, numerals used to identify features of the system  310  are incremented by a factor of three hundred (300) to identify like features of the system  10 . System  310  differs from system  10  primarily in that the nanoparticle-based sensor (sensor  50  in system  10 ) is disposed on a detachable or removable insertion member, here a cartridge  350   a , that is inserted into an insertion aperture, here insertion slot  350   b.    
       FIG. 14  shows various views of removable sensor cartridge  350   a . Sensor cartridge  350   a  comprises a substantially cylindrical member that comprises a handle at the top (that remains outside the housing after insertion into insertion slot  350   b ) and a cylindrical body that extends down into the similarly-substantially cylindrical insertion slot  350   b . Sensor cartridge  350   a  comprises a nanoparticle-based sensor  352  disposed on substantially planar PCB  354  that comprises edge connectors  364   a  (essentially identical to connectors  64  in  FIGS. 2-3 ). Sensor cartridge  350   a  comprises a substantially cylindrical channel  356  perpendicular to its long axis so that, when cartridge  356  is in its fully inserted and secured position in insertion slot  350   b , flow channel  326  is aligned with channel  356  so that the breath sample flows through channel  356  as part of flow channel  326  and in the process contacts sensor  352 . When cartridge  350   a  is fully inserted into insertion slot  305   b , edge connector  364   a  contacts corresponding contacts  364   b  at the bottom of insertion slot  350   b , which places sensor  352  in operative communication with measurement device PCT  380 . 
     System with Dual Sensors 
     In accordance with another aspect of the invention, systems, devices and methods are provided for measuring multiple analytes with a single device, and wherein protective and risk mitigation features as described herein are embodied. There are many examples of applications in which advantage may be found in measuring multiple analytes with a signal portable breath analyte measurement device. Acetone, oxygen and/or carbon dioxide, for example, may be used to monitor fat metabolism. Monitoring oxygen or carbon dioxide can provide information about an individual&#39;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 “driving under 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. When acetone is converted to isopropanol, however, a second problem can exist. When this conversion occurs, a breath acetone sensor may under-report 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 importance, 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, can enable superior health monitoring. In the case of diabetes, for instance, monitoring breath acetone, ammonia, and isoprene can serve as a rapid means to determine blood ketone, creatinine or blood-urea-nitrogen (“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. 
     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. 
     In addition, one also may wish to include a second sensor so that one of the sensors can serve as a reference. As an example, the first sensor may be constructed or selected to be selective for acetone, whereas the second sensor may be selective to an acetone interferent, such as water vapor. The sample breath sample is contact with each sensor, but the first sensor measures the acetone concentration while the second sensor measures the concentration of water vapor and thus the amount of interferent in the sample. This would permit the user or an analyst to subtract out the effects of the water vapor to obtain a normalized acetone measurement with respect to other breath samples having relatively more or less humidity. 
     A system  410  according to another embodiment is shown in  FIG. 15 . System  410  is very similar to system  10 , including many of the same components. Accordingly, numerals used to identify features of the system  400  are incremented by a factor of four hundred (400) to identify like features of the system  10 . The system  410  differs in that system  410  comprises at least two sensors subsystems, e.g., a nanoparticle-based sensor subsystem  450   a  and a second sensor subsystem  450   b , which may include a nanoparticle-based sensor but which may comprise other types of sensors. Each sensor subsystem comprises a sensor disposed in the flow path or in fluid communication with it. A pump  441  can be disposed downstream of sensor subsystems  450   a  and  b  to induce flow of the breath sample past the sensors and to contact them to obtain the analyte measurements. 
     In this embodiment, the breath sample can be inputted into measurement device  412  directly or via a breath bag  434 , past one-way valve  290  via posts  426   c  and into flow path  426 . The sample may flow through conditioning device  442  before entering chamber  426   a  and into contact with the sensors. The sample is then vented as shown in  FIGS. 1 and 10 . 
     System with Non-Linear Flow Path 
     A system  510  according to another embodiment is shown in  FIG. 16 . System  510  is very similar to system  10 , including many of the same components. Accordingly, numerals used to identify features of the system  500  are incremented by a factor of five hundred (500) to identify like features of the system  10 . The system  510  includes a non-linear flow path, comprising a first flow path  526   a , which delivers the breath sample to nanoparticle-based sensor  550 , and a second flow path  526   b , which continues the flow path to a one-way exit port valve  582 . 
     System with Heart Rate Monitor 
     A system  610  according to another embodiment is shown in  FIG. 17 . System  610  is very similar to system  10 , including many of the same components. Accordingly, numerals used to identify features of the system  600  are incremented by a factor of six hundred (600) to identify like features of the system  10 . 
     System  610  differs from system  10 , however, in that system  610  includes a heart rate monitor for measuring the heart rate of the user while the user uses the measurement device  612  to measure breath acetone concentration. Heart rate monitor comprises a pair of pads  699  disposed on the exterior of device housing  620 . 
     Material on Purging and Multiple Conditioning Devices 
     In certain instances, once the nanoparticle-based sensor has been exposed to the breath sample containing the acetone 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 important to remove any residual water/bacteria from the 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. 
     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 needs to 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. 18  is a functional block diagram illustrating the configuration of an embodiment 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 characteristics of the sensing device are then transmitted to a microprocessor for analysis, data logging, storage, and/or transmission. 
       FIG. 19  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&#39; 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 can be 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, such as 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° C. and into the sorbent trap held at 30° 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° 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 may comprise 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° 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° 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 (Fe 2 O 3 ) 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 can be 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, such as 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° C. and into the sorbent trap held at 30° 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° 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 may comprise 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° 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° 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 (Fe 2 O 3 ) nanoparticles manufactured using a sol-gel process with an average particle diameter of 20 nm doped with 33% w titanium dioxide (TiO 2 , 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 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, such as 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° C. and into the sorbent trap held at 30° 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° 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° C. A second nanoparticle-based sensor for acetone is operated with the nanoparticle material held at 160° 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° 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° 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 (Fe 2 O 3 ) 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 (Fe 2 O 3 ) nanoparticles manufactured using a sol-gel process with an average particle diameter of 20 nm doped with 33% w titanium dioxide (TiO 2 , 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. 20  is an embodiment of a hand-held breath gas analyzer with a sensing device, such as 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. 
       FIG. 21  is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment comprises an Fe 2 O 3  nanoparticle sensor. This sensor was tested in an environment with a continuous stream of gas (500 standard cubic centimeters per minute (“SCCM”)) mixed from compressed sources via mass flow controllers (to final percent volumes of 18% O 2 , 3% CO 2 , ppm levels of acetone, balance N 2 ). Under dry, continuous gas streams, the sensitivity of the nanoparticle sensors to acetone is very high and stable. 
       FIG. 22  is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment comprised an Fe 2 O 3  nanoparticle sensor. This sensor was tested with moderate amounts of humidity (20% relative humidity (“RH”) at 37° C.) added to the continuously supplied simulated breath (18% O 2 , 3% CO 2 , 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° C. (roughly 40% RH at 25° C.) with a 3% fluctuation band. Humidity can be a significant deterrent of acetone detection using the nanoparticle-based sensor without humidity mitigation strategies. 
       FIG. 23  is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment comprised an Fe 2 O 3  nanoparticle sensor. The sensor was tested in a flow chamber with 21% v/v O 2  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% O 2  and 3% CO 2 , balance N 2 , with acetone spikes where indicated. The sensor response to zero flow switched to sample flow (500 SCCM) with a concurrent change in O 2  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% O 2  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. 24  is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment comprised an Fe 2 O 3  nanoparticle sensor, using a conditioning device. The response of the sensor element to the various stages of breath sampling, as described in  FIG. 18 , is shown in  FIG. 23 . 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. 25  is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to acetone. This embodiment again utilizes an Fe 2 O 3  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. 24 . The last data point before the carrier gas switch-over is used for data normalization, a procedure which effectively removes minor baseline drifts.  FIG. 25  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% O 2 , and 3% CO 2  (balance nitrogen). 400 cc&#39;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. 25  represents the response of a nanoparticle-based sensor to acetone in simulated breath with characteristics that mimic human breath samples. 
       FIG. 26  is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to oxygen. This embodiment again utilizes an Fe 2 O 3  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. 26  demonstrates the ability of a nanoparticle-based sensor to measure oxygen in the presence of humidity. 
       FIG. 27  is a graph showing the sensitivity of an embodiment of a nanoparticle-based sensor to isopropyl alcohol. This embodiment uses a SnO 2  nanoparticle sensor. Carrier gas consisting of 18% v oxygen, 3% v CO 2 , 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. 
     Electrical Safety 
     In accordance with another aspect of the invention, systems, devices and methods are provided that comprise or provide electrical safety features for mitigating risks and adverse effects. Electrical safety is an important consideration for breath analysis devices that interface directly with a user, particularly for devices, e.g., such as measurement device  12  as shown in  FIG. 1 , wherein there is contact and interaction directly between the device and the user&#39;s respiratory tract. Electrical safety considerations include protection against over-voltage, electrostatic discharge, electrical surge, and the like. The use of battery power in breath analysis devices introduces the potential for further issues, e.g., such as battery over-charging, cross-polarity damage, and potentially meltdown or catastrophic failure of a battery pack. These issues are of particular concern in devices that make use of, for example, lithium ion batteries. Additional considerations of an electrical nature include protection from electromagnetic emissions, for example, associated with certain wireless communication components, and the like. 
     Adverse effects that may be caused by improper or inadequate consideration of electrical safety include, electrolysis of body tissues by passing direct current (“DC”) currents directly through body tissues, burns, muscle cramps, respiratory dysfunction or respiratory arrest, cardiac dysfunction or cardiac arrest, including ventricular fibrillation, and the like. 
     Certain embodiments of nanoparticle sensors are connected to a main power supply, such as a wall socket, capable of supplying alternating current (“AC”) directly from the power grid. These devices typically include a power cord, often with an integral grounding wire and grounding pin on the plug. Unfortunately, such devices may be subject to transient power surges from the main power line, AC frequency deviations, spurious line noise, etc. These electrical aberrations may cause circuit board, sensors, and other components of the device to function improperly, be damaged, or cease functioning entirely. For example, power surges may cause electrical shorts, or the like. Power or frequency deviations and line noise may decrease sensor sensitivities, and over-voltage may cause current or thermal run-away on a diode, transistor, or amplifier in the device. These issues can be troublesome and in some instances dangerous, particularly in the case of thermal run-away, because they can cause damage to the device or injury to the user, such as burns, electrical shocks, interference with pacemakers, and the like. Such devices would benefit from use of the safety devices described herein. 
     Certain embodiments of nanoparticle sensors are connected to a power main, but without a separate ground connection. Alternatively, these sensors may be connected to an auxiliary power supply, such as a Universal Serial Bus (“USB”) chipset on a computer, a portable charging pack or power supply, or the like. While the power cord of such devices may be insulated, the lack of grounding can cause challenges to performance and the potential for danger to a user. For example, electrostatic charge may build up on surfaces of the device, and may discharge when the user touches the device. This may be particularly troublesome if the device is in contact with a user&#39;s mouth or respiratory tract. Again, such devices would benefit from use of the safety devices described herein. 
     Other devices may be battery powered. Battery powered devices, while generally safe from the sometimes dramatic power fluctuations associated with main power lines, also have inherent risks. Battery packs, for example, may become extremely hot, which may cause burns to a user. Batteries may also leak corrosive or toxic chemicals and fluids, which is particularly dangerous for embodiments that come into contact with a user&#39;s mouth. Other examples, including embodiments that use lithium ion battery packs, may suffer catastrophic failures resulting in explosion, leaking, or combustion of the battery pack and the device. These dangers each pose potential but real threats to the user, and to the device. Furthermore, the power provided by the battery over the charge depletion period may adversely affect sensor and circuit performance. Again, such devices would benefit from use of the safety devices described herein. 
     There are three main mechanisms by which the user can generate physical harm if the sensor system is not properly designed:
         (1) battery leaks or overheats,   (2) power line surges or fast transients from A/C main are not rejected by the sensor system and components of the sensor system, e.g., the processor, are damaged, causing incorrect performance, and   (3) power line surges or fast transients from A/C main are not rejected by the sensor system and components of the sensor system, e.g., the processor, are damaged, causing improper signaling between components (e.g., overheating of a thermistor), which ultimately causes exposure to heavy metals from the nanoparticle sensor itself.       

     In certain embodiments, the power supply includes an isolation circuit for electrically isolating the devices electrical components from the power supply. An isolation circuit may include one or more isolation capacitors, an isolation transformer, or the like. 
     Additionally, an embodiment may include a power conditioning circuit configured to regulate the frequency of power supplied to operational components of the device. Such an embodiment, may include a phase-locked loop circuit, a frequency filter circuit, such as a low-pass circuit or band-pass circuit. In such embodiments, frequency anomalies from the main power line, and other power supplies. The present embodiments may further include a current limiting circuit configured to protect device components for electrical surges or from current run-away. The current limiting circuit may include one or more transistors or an amplifier configured in combination with one or more additional components such as resistors and capacitors for detecting when the current draw is over a threshold value, and then restricting or limiting the current supplied. For example, the power supply may be switched off. In another embodiment, a step-down circuit may reduce the voltage supplied by the power supply. 
     The present embodiments may include thermal sensor circuit configured to detect an over-temperature or thermal run-away condition. The thermal sensor may comprise, for example, a thermistor. In an embodiment, the thermal sensor may be coupled to a comparator circuit for comparing the temperature detected by the thermistor with a threshold value. If the temperature exceeds the threshold, then the power source may be switched off. Alternatively, the current or voltage supplied to the device may be limited by, for example, the current limiting circuit. 
     Additionally, the present embodiments may include one or more battery safety devices. For example, a battery safety device may include a physically restrictive device, such as an irregularly shaped receptacle for the battery configured to prevent improper installation of the battery. The battery safety device may also include a cross-polarization detection circuit configured to detect when the battery has been inserted incorrectly and to disable the device in response. In still other embodiments, the battery safety device may include a thermal detector configured to monitor the temperature of the battery pack. 
     Additional embodiments may include a voltage regulator circuit configured to ensure that the power supplied by the battery is within an acceptable range. For example, the voltage regulator circuit may limit the voltage supplied in response to a determination, e.g., with a comparator, that the supplied voltage is above a threshold. In another embodiment, the voltage regulator circuit may switch off power supplied by the battery, for example with a transistor or amplifier circuit, in response to a determination that the voltage supplied by the battery is under a threshold voltage. In certain embodiments, there may be an upper threshold and a lower threshold. 
     In one embodiment, the battery safety device may include a battery overcharge protection circuit configured to monitor a charging cycle of a battery and to restrict or shut off the charging current in response to a determination that the battery is charged up to a predetermined level. In an embodiment, the battery overcharge protection circuit may monitor a charging time. In another embodiment, the overcharge protection circuit may monitor a current or voltage supplied by the battery during the charge, and determine when the voltage or current exceed a predetermined threshold. 
     In some embodiments, the device may generate electromagnetic energy, which may interfere with the sensor, or medical equipment in a medical facility. For example, the present embodiments may include a wireless communication chipset or the like. In other embodiments, the power supplied via the power cord may generate electromagnetic energy. In such embodiments, an electromagnetic isolation device may be provided. An embodiment of an electromagnetic isolation device may include electromagnetic shielding of the power cord with, for example, a metal foil, a metallic braid, or the like. In still other embodiments, certain components such as transformers, may be housed in a metallic or other electromagnetically shielding material. In still other embodiments, an electromagnetic isolation circuit may be included, which for example, includes one or more isolation capacitors, resistors, transistors, or the like. 
     A representative electrical design and configuration for a nanoparticle-based sensor such as those described herein above is illustrated in  FIG. 2  for a single heater design, and in  FIG. 2  and  FIG. 3  for a dual heater design. In the former instance, the nanoparticle-based sensor subsystem comprises a four-terminal device (two leads for the sensor and two for the heater) and, in the latter, a six-terminal device (two lead for the sensor and two for each of the two heaters). This may be reduced, for example, by combining leads, e.g., by using a common power lead or a common ground lead. 
     A circuit diagram or schematic illustrating the electrical design and configuration for a nanoparticle-based sensor subsystem such as those described herein above is shown in  FIG. 28 , which may be used in conjunction with  FIG. 2  to better understand this illustrative embodiment. Nanoparticle-based sensor subsystem  950  comprises sensor  952  and heating device  966 , corresponding to sensor subsystem  50 , sensor  52  and heating device  66  of  FIG. 2 . The load or resistance of sensor  952  is represented in the drawing by R S  and that of heater  66  is represented by R H . A power supply  918 , such as battery pack  18  of  FIG. 1 , supplies DC power at a sensor voltage V S . To provide DC power to sensor  952 , sensor lead  962   a  (corresponding to lead  62   a  in  FIG. 2 ) is ohmicly coupled to the positive terminal of battery  918 . The other sensor lead  962   b  (corresponding to lead  62   b  in  FIG. 2 ) is coupled to a load resistor R L  and through it to the negative terminal of battery  918  or, equivalently in this embodiment, to ground. The value of load resistor R L  is selected to optimize the operating characteristics of sensor  952 , such as sensitivity and power consumption. Heating device  966  (corresponding to hearing device  66  in  FIG. 2 ) is coupled at its hot lead  970   a  to the positive terminal of battery  918  and heater lead  970   b  is coupled to ground, ( 970   a  and  b  here corresponding to leads  70   a  and  b  in  FIG. 2 ). 
     In operation, battery  918  provides power to both sensor  950  and heater  966 . The heater raises the temperature of sensor  950  to its operating temperature of about 400° C. When this operating temperature is achieved, the breath sample is passed over or through sensor  950 . Acetone in the breath sample selectively adsorbs onto or otherwise interacts with sensor  950  and in the process alters the resistivity RS of the sensor. This change in resistivity is sensed as a change in the voltage or potential difference V RL  outputted by sensor  952  at lead  962   b  relative to ground across load resistor R L . This potential difference V RL  comprises a sensor measurement signal that is reflective of the concentration of acetone in the breath sample (marked “gas sample” in  FIG. 28 ). 
     The representative circuitry for sensor  952  as shown in  FIG. 28 , although functional, lacks protection from such concerns as over voltage and electrostatic discharge (“ESD”). The problem is even more pronounced where an active power supply, such as an AC-supplied power supply  919  is used, as shown in  FIG. 28 . With the circuit of  FIG. 28 , particularly when using active power supply  919 , presents risks from power surge, over voltage, over current, ESD, electrical fast transient (“EFT”), and over charging. An over-voltage condition, for example, could cause heating device  966  to overheat, thus potentially threatening risk of injury to the mouth or respiratory tract of the user for a device such as measurement device  12  in  FIG. 1 . Such overheating also could damage sensor  952 . 
     To address and mitigation risks such as these, a system can be provided that comprises a measurement device for measuring acetone in the breath of a user, and an electronic device operatively coupled to the measurement device, wherein the measurement device comprises protective circuitry. The measurement device itself, including the incorporated protective circuitry, comprises another related but separate aspect of the invention. 
     In some embodiments, such a system comprises system  10  as shown in  FIG. 1  and subsequent figures, and may include the measurement device  12  in  FIG. 1  and subsequent figures, both modified to include the protective circuitry features described herein below. 
       FIG. 29  shows nanoparticle-based sensor system circuitry as described herein above with respect to  FIG. 28 , but which comprises protective circuitry  979  that mitigates or eliminates risks of damage or user injury. Protective circuitry  979  is also included in  FIG. 1  as circuitry  79 , in  FIG. 10  as circuitry  279 , in  FIG. 379  as  FIG. 13 , in  FIG. 15  as circuitry  479 , in  FIG. 16  as circuitry  579 , in  FIG. 17  as circuitry  679 . 
     In these embodiments, power is supplied to the circuit by a power supply that may comprise battery pack  918  or AC power supply  919 . For purposes of this illustration, the power supply is assumed to be AC power supply  919 . Power supply  919  operates on standard AC power and outputs a rectified DC voltage V IN . 
     The circuit may include first protective circuitry  990  that in turn comprises a diode  992  and a capacitor  994 . Diode  992  protects the circuit from reverse polarity conditions that could adversely affect system components, e.g., such as sensor  952 . Capacitor  994  buffers the circuit from transients and provides protection from EFTs. The output of first protective circuitry is a pair of lines  996  comprising a DC voltage and a ground. 
     The circuit may include second protective circuitry  998 , which provides over voltage protection, over current protection, and ESD protection. Circuitry  998  receives as inputs lines  996  from first protective circuitry  990 . The output from circuitry  998  is a pair of lines  999  that comprise a DC voltage and a ground. 
     The circuitry may include a first voltage regulator  918   a  that in this embodiment provides a steady output voltage of 3 volts (“v”), and a second voltage regulator  918   b  that in this embodiment provides a steady output voltage of 6 v. Each of the voltage regulators  918   a  and  918   b  receives as an input from circuit  998  the DC voltage and ground lines. 
     Voltage regulator  918   a  has as an output a first output terminal  918   a   1  that represents a high or 3 v line and a second output terminal  918   a   2  that represents a low or ground terminal. Similarly, voltage regulator  918   b  has a first output terminal  918   b   1  that represents a high or 6 v line and a second output terminal  918   a   2  that represents a low potential terminal. 
     Nanoparticle-based sensor  952  obtains its power from 3-volt regulator  918   a . High terminal  918   a   1  of regulator  918   a  is coupled to nanoparticle-based sensor lead  962   a  (corresponding to lead  62   a  of  FIG. 2 ). Sensor lead  962   b  is coupled to load resistor R L  and through it to ground  918   a   2 . High terminal  918   a   1  also is provided to processor  980  (corresponding to the processor on PCB  80  in  FIG. 1 ), as explained more fully herein below. The output of sensor  952  is provided to processor  980  via coupling to terminal  962   b  and via coupling to ground, across load resistor R L . The sensor measurement signal outputted by sensor  952  and reflective of the concentration of acetone in the breath sample is provided by the voltage or potential difference V RL  across these leads. 
     Heating device  966  obtains its power from 6-volt regulator  918   b . High terminal  918   b   1  is coupled to lead  970   a  of heater  966  and terminal  918   b   2  is coupled to lead  970   b  of heater  966  ( 970   a  and  b  here corresponding to leads  70   a  and  b  in  FIG. 2 ). 
     This circuit embodiment incorporates power protection capabilities in the form of diode  992  (for inverse polarity protection), capacitor  994  (for EFT protection), and second protective circuitry  998  for over voltage and over current conditions and ESD protection. These protective circuit elements can ensure that there is a safe power source for the system. 
     This circuit embodiment further incorporates voltage regulators to ensure that the power output is clean and stable. This design incorporates multiple regulators to power the heating element as well as the sensor circuit and the other system circuit (for example, the processor) with the option of providing different voltages. 
     In addition, this embodiment incorporates a microprocessor that is connected across R L  of the sensor circuit. The ends of the R L  resistor are attached to ADC pins on the microprocessor to measure the voltage drop across R L . The processor is also attached to other peripherals that may make use of the sensor output. 
     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. 
     Terminology 
     Although certain embodiments have been described herein with respect to breath measurement systems and methods for measuring acetone, the systems described herein can detect other analytes, such as oxygen, ketone, ammonia, isoprene, ethanol, isopropanol, and/or carbon dioxide, in addition to or instead of acetone. 
     Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that some embodiments include, while other embodiments do not include, certain features, elements, and/or states. Thus, such conditional language is not generally intended to imply that features, elements, blocks, and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. 
     The ranges disclosed herein also encompass any and all overlap, sub-ranges, and combinations thereof. Language such as “up to,” “at least,” “greater than,” “less than,” “between,” and the like includes the number recited. For example, “about 150° C.” includes “150° C.” Numbers preceded by a term such as “about,” “substantially,” or “approximately” include the recited numbers and should be interpreted based on the circumstances (e.g., as accurate as reasonably possible under the circumstances, for example ±1%, ±5%, ±10%, ±15%, etc.). 
     Although certain embodiments and examples have been described herein, it will be understood by those skilled in the art that many aspects of the delivery systems shown and described in the present disclosure may be differently combined and/or modified to form still further embodiments or acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure. A wide variety of designs and approaches are possible. No feature, structure, or step disclosed herein is essential or indispensable. 
     For purposes of this disclosure, certain aspects, advantages, and novel features are described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     Moreover, while illustrative embodiments have been described herein, the scope of any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. Further, the actions of the disclosed processes and methods may be modified in any manner, including by reordering actions and/or inserting additional actions and/or deleting actions. It is intended, therefore, that the specification and examples be considered as illustrative only, with a true scope and spirit being indicated by the claims and their full scope of equivalents.