Source: https://patents.google.com/patent/EP1850114A1/en
Timestamp: 2019-07-22 19:51:33
Document Index: 83060554

Matched Legal Cases: ['Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 10']

EP1850114A1 - Spectroscopic method of determining an analyte concentration in a sample - Google Patents
Spectroscopic method of determining an analyte concentration in a sample Download PDF
EP1850114A1
EP1850114A1 EP07015609A EP07015609A EP1850114A1 EP 1850114 A1 EP1850114 A1 EP 1850114A1 EP 07015609 A EP07015609 A EP 07015609A EP 07015609 A EP07015609 A EP 07015609A EP 1850114 A1 EP1850114 A1 EP 1850114A1
EP07015609A
2002-12-12 Priority to EP20020794266 priority patent/EP1454126B1/en
2007-10-31 Publication of EP1850114A1 publication Critical patent/EP1850114A1/en
This application claims priority to U.S. Provisional Patent Application No. 60/341,435 filed December 14, 2001 and U.S. Provisional Patent Application No. 60/357,264 filed February 12, 2002 , both of which are incorporated in their entireties by reference herein.
In certain other embodiments, a method provides pathlength insensitive measurements of blood constituents in a sample using infrared (IR) spectroscopy. The method comprises providing an absorbance spectrum of the sample. The method further comprises shifting the absorbance spectrum to zero at an isosbestic wavelength, wherein water and a protein within the sample have approximately equivalent absorptions at the isosbestic wavelength.
FIGURE 14 is a perspective view of one embodiment of a cuvette for use with the reagentless whole-blood detection system.
FIGURE 15 is a plan view of another embodiment of a cuvette for use with the reagentless whole-blood detection system.
FIGURE 18 is a flow diagram of one embodiment of a method for using spectroscopy to determine an analyte concentration in a sample.
FIGURE 19 is a graph illustrating one isosbestic point between approximately 4.0 and 4.2 µm in the absorbance spectra of water and whole blood protein.
FIGURE 20 is a graph illustrating another isosbestic point between approximately 9.2 µm and 9.6 µm in the absorbance spectra of water and whole blood protein.
FIGURE 21 is a graph illustrating progressive removal of free water contributions from an absorbance spectrum of a sample.
FIGURE 22 is a graph illustrating determination of free protein from an absorbance spectrum of a sample.
FIGURE 23 is a graph illustrating progressive removal of residual interactive component contributions from an absorbance spectrum of a sample.
FIGURE 24 is a graph illustrating an absorbance spectrum with residual absorbance after glucose spectral data removal used for individual determination of residual components.
FIGURE 25 is a flow diagram of one embodiment of a method of providing pathlength insensitive measurements of blood constituents in a sample using infrared (IR) spectroscopy.
As used herein, the term "noninvasive" is a broad term and is used in its ordinary sense and refers, without limitation, to analyte detection devices and methods which have the capability to determine the concentration of an analyte in in-vivo tissue samples or bodily fluids. It should be understood, however, that the noninvasive system 10 disclosed herein is not limited to noninvasive use, as the noninvasive system 10 may be employed to analyze an in-vitro fluid or tissue sample which has been obtained invasively or noninvasively. As used herein, the term "invasive" (or, alternatively, "traditional") is a broad term and is used in its ordinary sense and refers, without limitation; to analyte detection methods which involve the removal of fluid samples through the skin. As used herein, the term "material sample" is a broad term and is used in its ordinary sense and refers, without limitation, to any collection of material which is suitable for analysis by the noninvasive system 10. For example, the material sample S may comprise a tissue sample, such as a human forearm, placed against the noninvasive system 10. The material sample S may also comprise a volume of a bodily fluid, such as whole blood, blood component(s), interstitial fluid or intercellular fluid obtained invasively, or saliva or urine obtained noninvasively, or any collection of organic or inorganic material. As used herein, the term "analyte" is a broad term and is used in its ordinary sense and refers, without limitation, to any chemical species the presence or concentration of which is sought in the material sample S by the noninvasive system 10. For example, the analyte(s) which may be detected by the noninvasive system 10 include but not are limited to glucose, ethanol, insulin, water, carbon dioxide, blood oxygen, cholesterol, bilirubin, ketones, fatty acids, lipoproteins, albumin, urea, creatinine, white blood cells, red blood cells, hemoglobin, oxygenated hemoglobin, carboxyhemoglobin, organic molecules, inorganic molecules, pharmaceuticals, cytochrome, various proteins and chromophores, microcalcifications, electrolytes, sodium, potassium, chloride, bicarbonate, and hormones. As used herein to describe measurement techniques, the term "continuous" is a broad term and is used in its ordinary sense and refers, without limitation, to the taking of discrete measurements more frequently than about once every 10 minutes, and/or the taking of a stream or series of measurements or other data over any suitable time interval, for example, over an interval of one to several seconds, minutes, hours, days, or longer. As used herein to describe measurement techniques, the term "intermittent" is a broad term and is used in its ordinary sense and refers, without limitation, to the taking of measurements less frequently than about once every 10 minutes.
Still referring to FIGURE 2, the heater layer 34 preferably comprises a first adhesion layer of gold or platinum (hereinafter referred to as the "gold" layer) deposited over an alloy layer which is applied to the main layer 32. The alloy layer comprises a material suitable for implementation of the heater layer 34, such as, by way of example, 10/90 titanium/tungsten, titanium/platinum, nickel/chromium, or other similar material. The gold layer preferably has a thickness of about 4000 Å, and the alloy layer preferably has a thickness ranging between about 300 Å and about 500 Å. The gold layer and/or the alloy layer may be deposited onto the main layer 32 by chemical deposition including, but not necessarily limited to, vapor deposition, liquid deposition, plating, laminating, casting, sintering, or other forming or deposition methodologies well known to those or ordinary skill in the art. If desired, the heater layer 34 may be covered with an electrically insulating coating which also enhances adhesion to the main layer 32. One preferred coating material is aluminum oxide. Other acceptable materials include, but are not limited to, titanium dioxide or zinc selenide.
In a preferred embodiment, the window assembly 12 comprises substantially only the main layer 32 and the heater layer 34. Thus, when installed in an optical detection system such as the noninvasive system 10 shown in FIGURE 1, the window assembly 12 will facilitate a minimally obstructed optical path between a (preferably flat) upper surface 12a of the window assembly 12 and the infrared detectors 28 of the noninvasive system 10. The optical path 32 in the preferred noninvasive system 10 proceeds only through the main layer 32 and heater layer 34 of the window assembly 12 (including any antireflective, index-matching, electrical insulating or protective coatings applied thereto or placed therein), through the optical mixer 20 and collimator 22 and to the detectors 28.
Except as noted below, the heater layer 44 is generally similar to the heater layer 34 employed in the window assembly shown in FIGURE 2. Alternatively, the heater layer 44 may comprise a doped infrared-transmissive material, such as a doped silicon layer, with regions of higher and lower resistivity. The heater layer 44 preferably has a resistance of about 2 ohms and has a preferred thickness of about 1,500 angstroms. A preferred material for forming the heater layer 44 is a gold alloy, but other acceptable materials include, but are not limited to, platinum, titanium, tungsten, copper, and nickel.
As shown in FIGURE 6B, first and second clamping plates 450 and 452 may be used to clamp the portions of the window mounting system 400 to one another. For example, the second clamping plate 452 is configured to clamp the window assembly 12 and the first PCB 402 to the diffuser 410 with screws or other fasteners extending through the openings shown in the second clamping plate 452, the heat spreader layer 412 and the conductive layer 414. Similarly, the first clamping plate 450 is configured overlie the second clamping plate 452 and clamp the rest of the window mounting system 400 to the heat sink 419, thus sandwiching the second clamping plate 452, the window assembly 12, the first PCB 402, the diffuser 410, the second PCB 403, and the TEC 418 therebetween. The first clamping plate 450 prevents undesired contact between the sample S and any portion of the window mounting system 400, other than the window assembly 12 itself Other mounting plates and mechanisms may also be used as desired.
The filters 24 preferably comprise standard interference-type infrared filters, widely available from manufacturers such as Optical Coating Laboratory, Inc. ("OCLI") of Santa Rosa, CA. In the embodiment illustrated in FIGURE 1, a 3 x 4 array of filters 24 is positioned above a 3 x 4 array of detectors 28 and concentrators 26. As employed in this embodiment, the filters 24 are arranged in four groups of three filters having the same wavelength sensitivity. These four groups have bandpass center wavelengths of 7.15 µm ± 0.03 µm, 8.40 µm ± 0.03 µm, 9.48 µm ± 0.04 µm, and 11.10 µm ± 0.04 µm, respectively, which correspond to wavelengths around which water and glucose absorb electromagnetic radiation. Typical bandwidths for these filters range from 0.20 µm to 0.50 µm.
A watchdog timer 94 may be employed to ensure that the processor 74 is operating correctly. If the watchdog timer 94 does not receive a signal from the processor 74 within a specified time, the watchdog timer 94 resets: the processor 74. The control system may also include a JTAG interface 96 to enable testing of the noninvasive system 10.
As shown in FIGURE 8, a first reference signal P may be measured at a first reference wavelength. The first reference signal P is measured at a wavelength where water strongly absorbs (e.g., 2.9 µm or 6.1 µm). Because water strongly absorbs radiation at these wavelengths, the detector signal intensity is reduced at those wavelengths. Moreover, at these wavelengths water absorbs the photon emissions emanating from deep inside the sample. The net effect is that a signal emitted at these wavelengths from deep inside the sample is not easily detected. The first reference signal P is thus a good indicator of thermal-gradient effects near the sample surface and may be known as a surface reference signal. This signal may be calibrated and normalized, in the absence of heating or cooling applied to the sample, to a baseline value of 1. For greater accuracy, more than one first reference wavelength may be measured. For example, both 2.9 µm and 6.1 µm may be chosen as first reference wavelengths.
As further shown in FIGURE 8, a second reference signal R may also be measured. The second signal R may be measured at a wavelength where water has very low absorbance (e.g., 3.6 µm or 4.2 µm). This second reference signal R thus provides the analyst with information concerning the deeper regions of the sample, whereas the first signal P provides information concerning the sample surface. This signal may also be calibrated and normalized, in the absence of heating or cooling applied to the sample, to a baseline value of 1. As with the first (surface) reference signal P, greater accuracy may be obtained by using more than one second (deep) reference signal R
In order to determine analyte concentration, a third (analytical) signal Q is also measured. This signal is measured at an IR absorbance peak of the selected analyte. The IR absorbance peaks for glucose are in the range of about 6.5 µm to 11.0 µm. This detector signal may also be calibrated and normalized, in the absence of heating or cooling applied to the material sample S, to a baseline value of 1. As with the reference signals P, R, the analytical signal Q may be measured at more than one absorbance peak.
Simultaneously, the second reference signal R is monitored. Since the second reference signal R corresponds to the radiation characteristics of deeper regions of the sample, which do not cool as rapidly as the surface (due to the time needed for the surface cooling to propagate into the deeper regions of the sample), the intensity of signal R does not decline until slightly later. Consequently, the signal R does not reach the magnitude 150 until some later time tR. In other words, there exists a time delay between the time tP at which the amplitude of the first reference signal P reaches the checkpoint 150 and the time tR at which the second reference signal R reaches the same checkpoint 150. This time delay can be expressed as a phase difference Φ(λ). Additionally, a phase difference may be measured between the analytical signal Q and either or both reference signals P, R
As the concentration of analyte increases, the amount of absorbance at the analytical wavelength increases. This reduces the intensity of the analytical signal Q in a concentration-dependent way. Consequently, the analytical signal Q reaches intensity 150 at some intermediate time tQ. The higher the concentration of analyte, the more the analytical signal Q shifts to the left in FIGURE 8. As a result, with increasing analyte concentration, the phase difference Φ(λ) decreases relative to the first (surface) reference signal P and increases relative to the second (deep tissue) reference signal R The phase difference(s) Φ(λ) are directly related to analyte concentration and can be used to make accurate determinations of analyte concentration.
The phase difference Φ(λ) between the first (surface) reference signal P and the analytical signal Q is represented by the equation: Φ λ = t P - t Q
The phase difference Φ(λ) between the second (deep tissue) reference signal R and the analytical signal Q signal is represented by the equation: Φ λ = t Q - t R
As previously explained in the discussions relating to FIGURE 8, the phase difference Φ(λ) may be measured and used to determine analyte concentration. FIGURE 9 shows that the first (surface) reference signal J declines and rises in intensity first The second (deep tissue) reference signal L declines and rises in a time-delayed manner relative to the first reference signal J. The analytical signal K exhibits a time/phase delay dependent on the analyte concentration. With increasing concentration, the analytical signal K shifts to the left in FIGURE 9. As with FIGURE 8, the phase difference Φ(λ) may be measured. For example, a phase difference Φ(λ) between the second reference signal L and the analytical signal K, may be measured at a set amplitude 162 as shown in FIGURE 9. Again, the magnitude of the phase signal reflects the analyte concentration of the sample.
The phase-difference information compiled by any of the methodologies disclosed herein can correlated by the control system 30 (see FIGURE 1) with previously determined phase-difference information to determine the analyte concentration in the sample. This correlation could involve comparison of the phase-difference information received from analysis of the sample, with a data set containing the phase-difference profiles observed from analysis of wide variety of standards of known analyte concentration. In one embodiment, a phase/concentration curve or regression model is established by applying regression techniques to a set of phase-difference data observed in standards of known analyte concentration. This curve is used to estimate the analyte concentration in a sample based on the phase-difference information received from the sample.
As an alternative or as a supplement to measuring phase difference(s), differences in amplitude between the analytical and reference signal(s) may be measured and employed to determine analyte concentration. Additional details relating to this technique and not necessary to repeat here may be found in the Assignee's U.S. patent application serial no. 09/538,164 , incorporated by reference below.
It has been found that when analyzing a sample of human skin, a temperature event of 10° C creates a thermal gradient which penetrates to a depth of about 150 µm, after about 500 ms of exposure. Consequently, a cooling/heating cycle or driving frequency of 1 Hz provides information to a depth of about 150 µm. It has also been determined that exposure to a temperature event of 10° C for about 167 ms creates a thermal gradient that penetrates to a depth of about 50 µm. Therefore, a cooling/heating cycle of 3 Hz provides information to a depth of about 50 µm. By subtracting the detector signal information measured at a 3 Hz driving frequency from the detector signal information measured at a 1 Hz driving frequency, one can determine the analyte concentration(s) in the region of skin between 50 and 150 µm. Of course, a similar approach can be used to determine analyte concentrations at any desired depth range within any suitable type of sample.
As shown in FIGURE 11, alternating deep and shallow thermal gradients may be induced by alternating slow and fast driving frequencies. As with the methods described above, this variation also involves the detection and measurement of phase differences Φ(λ) between reference signals G, G' and analytical signals H, H'. Phase differences are measured at both fast (e.g., 3 Hz) and slow (e.g., 1 Hz) driving frequencies. The slow driving frequency may continue for an arbitrarily chosen number of cycles (in region SL1), for example, two full cycles. Then the fast driving frequency is employed for a selected duration, in region F1. The phase difference data is compiled in the same manner as disclosed above. In addition, the fast frequency (shallow sample) phase difference data may be subtracted from the slow frequency (deep sample) data to provide an accurate determination of analyte concentration in the region of the sample between the gradient penetration depth associated with the fast driving frequency and that associated with the slow driving frequency.
Additional details not necessary to repeat here may be found in U.S. Patent No. 6,198,949 , titled SOLID-STATE NON-INVASIVE INFRARED ABSORPTION SPECTROMETER FOR THE GENERATION AND CAPTURE OF THERMAL GRADIENT SPECTRA FROM LIVING TISSUE, issued March 6, 2001; U.S. Patent No. 6,161,028 , titled METHOD FOR DETERMINING ANALYTE CONCENTRATION USING PERIODIC TEMPERATURE MODULATION AND PHASE DETECTION, issued December 12, 2000; U.S. Patent No. 5,877,500 , titled MULTICHANNEL INFRARED DETECTOR WITH OPTICAL CONCENTRATORS FOR EACH CHANNEL, issued on March 2, 1999; U.S. Patent Application Serial No. 09/538,164, filed March 30, 2000 and titled METHOD AND APPARATUS FOR DETERMINING ANALYTE CONCENTRATION USING PHASE AND MAGNITUDE DETECTION OF A RADIATION TRANSFER FUNCTION; U.S. Provisional Patent Application No. 60/336,404, filed October 29, 2001 , titled WINDOW ASSEMBLY; U.S. Provisional Patent Application No. 60/340,435, filed December 12, 2001 , titled CONTROL SYSTEM FOR BLOOD CONSTITUENT MONITOR; U.S. Provisional Patent Application No. 60/340,654, filed December 12, 2001 , titled SYSTEM AND METHOD FOR CONDUCTING AND DETECTING INFRARED RADIATION; U.S. Provisional Patent Application No. 60/336,294, filed October 29, 2001 , titled METHOD AND DEVICE FOR INCREASING ACCURACY OF BLOOD CONSTITUENT MEASUREMENT; and U.S. Provisional Patent Application No. 60/339,116, filed November 7, 2001 , titled METHOD AND APPARATUS FOR IMPROVING CLINICALLY SIGNIFICANT ACCURACY OF ANALYTE MEASUREMENTS. The entire disclosure of all of the above-mentioned patents, patent applications and publications is hereby incorporated by reference herein and made a part of this specification.
The radiation source 220 of the whole-blood system 200 emits electro-magnetic radiation in any of a number of spectral ranges, e.g., within infrared wavelengths; in the mid-infrared wavelengths; above about 0.8 µm; between about 5.0 µm and about 20.0 µm; and/or between about 5.25 µm and about 12.0 µm. However, in other embodiments the whole-blood system 200 may employ a radiation source 220 which emits in wavelengths found anywhere from the visible spectrum through the microwave spectrum, for example anywhere from about 0.4 µm to greater than about 100 µm. In still further embodiments the radiation source emits electromagnetic radiation in wavelengths between about 3.5 µm and about 14 µm, or between about 0.8 µm and about 2.5 µm, or between about 2.5 µm and about 20 µm, or between about 20 µm and about 100 µm, or between about 6.85 µm and about 10.10 µm.
The filter 230 permits electromagnetic radiation of selected wavelengths to pass through and impinge upon the cuvette/sample element 240. Preferably, the filter 230 permits radiation at least at about the following wavelengths to pass through to the cuvette/sample element: 3.9, 4.0 µm, 4.05 µm, 4.2 µm, 4.75, 4.95 µm, 5:25 µm, 6.12 µm, 7.4 µm, 8.0 µm, 8.45 µm, 9.25 µm, 9.5 µm, 9.65 µm, 10.4 µm, 12.2 µm. In another embodiment, the filter 230 permits radiation at least at about the following wavelengths to pass through to the cuvette/sample element: 5.25 µm, 6.12 µm, 6.8 µm, 8.03 µm 8.45 µm, 9.25 µm, 9.65 µm, 10.4 µm, 12 µm. In still another embodiment, the filter 230 permits radiation at least at about the following wavelengths to pass through to the cuvette/sample element: 6.85 µm, 6.97 µm, 7.39 µm, 8.23 µm, 8.62 µm, 9.02 µm, 9.22 µm, 9.43 µm, 9.62 µm, and 10.10 µm. The sets of wavelengths recited above correspond to specific embodiments within the scope of this disclosure. Furthermore, other subsets of the foregoing sets or other combinations of wavelengths can be selected. Finally, other sets of wavelengths can be selected within the scope of this disclosure based on cost of production, development time, availability, and other factors relating to cost, manufacturability, and time to market of the filters used to generate the selected wavelengths, and/or to reduce the total number of filters needed.
Additional information on laser lances can be found in U.S. Patent No. 5,908,416, issued June 1, 1999 , titled LASER DERMAL PERFORATOR; the entirety of this patent is hereby incorporated by reference herein and made a part of this specification. One suitable gas-jet, fluid-jet or particle-jet perforator is disclosed in U.S. Patent No. 6,207,400, issued March 27, 2001 , titled NON- OR MINIMALLY INVASIVE MONITORING METHODS USING PARTICLE DELIVERY METHODS; the entirety of this patent is hereby incorporated by reference herein and made a part of this specification. One suitable iontophoretic sampler is disclosed in U.S. Patent No. 6,298,254, issued October 2, 2001 , titled DEVICE FOR SAMPLING SUBSTANCES USING ALTERNATING POLARITY OF IONTOPHORETIC CURRENT; the entirety of this patent is hereby incorporated by reference herein and made a part of this specification. One suitable ultrasonic enhancer, and chemical enhancers suitable for use therewith, are disclosed in U.S. Patent No. 5,458,140 , titled ENHANCEMENT OF TRANSDERMAL MONITORING APPLICATIONS WITH ULTRASOUND AND CHEMICAL ENHANCERS, issued October 17, 1995, the entire disclosure of which is hereby incorporated by reference and made a part of this specification.
The windows 244, 246 are made of polypropylene in one embodiment. In another embodiment, the windows 244, 246 are made of polyethylene. Polyethylene and polypropylene are materials having particularly advantageous properties for handling and manufacturing, as is known in the art. Also, polypropylene can be arranged in a number of structures, e.g., isotactic, atactic and syndiotactic, which may enhance the flow characteristics of the sample in the sample element. Preferably the windows 244, 246 are made of durable and easily manufactureable materials, such as the above-mentioned polypropylene or polyethylene, or silicon or any other suitable material. The windows 244, 246. can be made of any suitable polymer, which can be isotactic, atactic or syndiotactic in structure.
The distance between the windows 244, 246 comprises an optical pathlength and can be between about 1 µm and about 100 µm. In one embodiment, the optical pathlength is between about 10 µm and about 40 µm, or between about 25 µm and about 60 µm, or between about 30 µm and about 50 µm. In still another embodiment, the optical pathlength is about 25 µm. The transverse size of each of the windows 244, 246 is preferably about equal to the size of the detector 250. In one embodiment, the windows are round with a diameter of about 3 mm. In this embodiment, where the optical pathlength is about 25 µm the volume of the sample cell 242 is about 0.177 µL. In one embodiment, the length of the sample supply passage 248 is about 6 mm, the height of the sample supply passage 248 is about 1 mm, and the thickness of the sample supply passage 248 is about equal to the thickness of the sample cell, e.g., 25 µm. The volume of the sample supply passage is about 0.150 µL. Thus, the total volume of the cuvette 240 in one embodiment is about 0.327 µL. Of course, the volume of the cuvette 240/sample cell 242/etc. can vary, depending on many variables, such as the size and sensitivity of the detectors 250, the intensity of the radiation emitted by the source 220, the expected flow properties of the sample, and whether flow enhancers (discussed below) are incorporated into the cuvette 240. The transport of fluid to the sample cell 242 is achieved preferably through capillary action, but may also be achieved through wicking, or a combination of wicking and capillary action.
FIGURES 15-17 depict another embodiment of a cuvette 305 that could be used in connection with the whole-blood system 200. The cuvette 305 comprises a sample cell 310, a sample supply passage 315, an air vent passage 320, and a vent 325. As best seen in FIGURES 16,16A and 17, the cuvette also comprises a first sample cell window 330 having an inner side 332, and a second sample cell window 335 having an inner side 337. As discussed above, the window(s) 330/335 in some embodiments also comprise sample cell wall(s). The cuvette 305 also comprises an opening 317 at the end of the sample supply passage 315 opposite the sample cell 310. The cuvette 305 is preferably about 1/4 - 1/8 inch wide and about 3/4 inch long; however, other dimensions are possible while still achieving the advantages of the cuvette 305.
The sample cell 310 is defined between the inner side 332 of the first sample cell window 330 and the inner side 337 of the second sample cell window 335. The perpendicular distance T between the two inner sides 332, 337 comprises an optical pathlength that can be between about 1 µm and about 1.22 mm. The optical pathlength can alternatively be between about 1 µm and about 100 µm. The optical pathlength could still alternatively be about 80 µm, but is preferably between about 10 µm and about 50 µm. In another embodiment, the optical pathlength is about 25 µm. The windows 330, 335 are preferably formed from any of the materials discussed above as possessing sufficient radiation transmissivity. The thickness of each window is preferably as small as possible without overly weakening the sample cell 310 or cuvette 305.
The second layer 355 may be formed entirely of an adhesive that joins the first and third layers 350, 360. In other embodiments, the second layer may be formed from similar materials as the first and third layers, or any other suitable material. The second layer 355 may also be formed as a carrier with an adhesive deposited on both sides thereof. The second layer 355 forms the sample supply passage 315, the air vent passage 320, and the sample cell 310. The thickness of the second layer 355 can be between about 1 µm and about 1.22 mm. This thickness can alternatively be between about 1 µm and about 100 µm. This thickness could alternatively be about 80 µm, but is preferably between about 10 µm and about 50 µm. In another embodiment, the second layer thickness is about 25 µm.
Further information can be found in U.S. Patent Application No. 10/055,875, filed January 21, 2002 , titled REAGENT-LESS WHOLE-BLOOD GLUCOSE METER. The entire contents of this patent application is incorporated by reference herein and made a part of this specification.
FIGURE 18 is a flow diagram of one embodiment of a method 500 for using spectroscopy to determine an analyte concentration in a sample. In an operational block 510, the method 500 comprises producing an absorbance spectrum of the sample. In an operational block 520, the method 500 further comprises shifting the absorbance spectrum to zero in a wavelength region. In an operational block 530, the method 500 further comprises subtracing a water or other substance contribution from the absorbance spectrum.
In an exemplary embodiment, blood was simulated in its major components using bovine serum albumin (BSA) for total blood protein and saline for serum. Infrared absorbance or optical density (OD) spectra of the samples were measured with a Fourier-Transform Infrared (FTIR) instrument from Perkin-Elmer, Inc. of Wellseley, Massachusettes. As used herein, the term "optical density" or "OD" is synonymous with the term "absorbance." Cuvette pathlength was set with different spacers between BaF2 windows at 32 and 20 micrometers. The fringe pattern of the empty cuvette was used for calculation of the actual optical pathlength inside the cuvette. Flexible tubing and the flow-through type of the cuvette allowed for repeated filling with different solutions without changes being made to the experimental setup. Instrument drift and baseline deviations were accounted for with saline reference measurements before and after sample measurements. A total of 100 scans were collected per sample over a period of about 5 minutes. Scanned data were stored in ASCII format and transferred to an electronic spreadsheet program (e.g., Lotus 1-2-3 from IBM Corp. of Armonk, New York) for evaluation.
It was discovered that changes of the protein to water ratio, equivalent to changes of hematocrit in blood, produce at least 2 isosbestic points on the wavelength scale, where the components protein and water exhibit identical IR absorbance, one of them at about 4 µm and the other at about 9.4 µm for BSA in water. As seen in FIGURE 19 and FIGURE 20, the effective isosbestic point can be expected to be somewhat different for different proteins in different solutions. The important and unexpected aspect of this observation is that these wavelength ranges can be used to obtain a current measure of effective optical pathlength in the filled cuvette, either before or during measurements at other wavelength ranges. Such information is very useful in subsequent calculations for compensation of instrument-related pathlength non-linearities.
It was also discovered that after setting transmittance to zero at one or both wavelengths ranges of high water absorbance at 6.08 and/or 12.25 µm, thereby shifting absorbance to zero preferably at the lower isosbestic point, will result in spectral data at baseline. In FIGURE 21, we can see the higher isosbestic point which may be used also but it is partially contaminated with absorbances of blood components that are present at low concentration levels.
It was also discovered that the absorbance peak centered around 4.7 µm, is almost entirely due to free water absorbance and can be advantageously used for determination of free water in the sample: the correct subtraction of absorbance of a stored reference water across the entire wavelength range is achieved when there is zero residual absorbance left between approximately 4.5 and 5 µm, shown in FIGURE 21.
It was also discovered that prior knowledge of optical pathlength, based on the total sample absorbance at the isosbestic point as well as on water absorbance between approximately 4.5 and 5 µm, allows for the use of the correct reference water spectrum that is compensated for non-linearities at all wavelengths. This is advantageous for distortion-free presentation of final results.
It was also discovered that the absorbance peak centered around 7.1 µm, is almost entirely due to free protein absorbance and can be advantageously used for determination of free protein in the sample: the correct subtraction of absorbance of a stored reference hydrated protein across the entire wavelength range is achieved when there is zero residual absorbance left between approximately 7.0 and 7.2 µm or alternatively, at a different protein absorbance such as the range from approximately 7.9 to 8.1 µm or alternatively, a predefined residual at a combination of wavelength ranges, as shown in FIGURE 22.
It was also discovered that prior knowledge of optical pathlength based on total sample absorbance at the isosbestic point as well as on total protein absorbance between approximately 7.0 and 7.2 µm, or alternatively, on a different protein absorbance such as the range from approximately 7.9 to 8.1 µm, allows for the use of the correct reference protein spectrum that is compensated for non-linearities at all wavelengths. This is advantageous for distortion-free presentation of final results.
FIGURE 23 shows that it was also discovered that repetition of the last two steps of water and protein removal from the complete sample, will result in further removal of smaller residual interactive components, most likely representing components of the boundary layer between water and protein.
It was also discovered that the resulting instrument drift corrected, water-, protein-, interactive components-removed, and optical pathlength and major component induced distortion-free spectral data can be fitted with reference glucose spectral data at one or more glucose absorbance maxima such as 9.25 and 9.65 µm to yield a measure for glucose in the original sample. The residual absorbance after glucose spectral data removal may be used further for individual determination of residual components. In certain embodiments, the residual components include high molecular weight substances, including but not limited to, other proteins, albumin, hemoglobin, fibrinogen, lipoproteins, and trasferrin. In certain other embodiments, the residual components include low molecular weight substances, including but not limited to, urea, lactate, and vitamin C. The final glucose measure may be corrected for the presence of such lower level potentially interfering substances by subtracting reference spectra of specific substances, such as urea, from the residual data, as shown in FIGURE 24.
The methods disclosed herein may be used in connection with apparatus and or methods disclosed in U.S. Patent No. 6,198,949 , titled SOLID-STATE NON-INVASIVE INFRARED ABSORPTION SPECTROMETER FOR THE GENERATION AND CAPTURE OF THERMAL GRADIENT SPECTRA FROM LIVING TISSUE, issued March 6, 2001; U.S. Patent No. 6,161,028 , titled METHOD FOR DETERMINING ANALYTE CONCENTRATION USING PERIODIC TEMPERATURE MODULATION AND PHASE DETECTION, issued December 12, 2000; U.S. Patent Application Serial No. 09/538,164, filed March 30, 2000 and titled METHOD AND APPARATUS FOR DETERMINING ANALYTE CONCENTRATION USING PHASE AND MAGNITUDE DETECTION OF A RADIATION TRANSFER FUNCTION; and WIPO PCT Publication No. WO 01/30236 (corresponding to U.S. Patent Application Serial No. 09/427,178), published May 3, 2001 , titled SOLID-STATE NON-INVASIVE THERMAL CYCLING SPECTROMETER The entire disclosures of all of the above-mentioned patents, patent applications and publications re hereby incorporated by reference herein and made a part of this specification.
FIGURE 25 is a flow diagram of one embodiment of a method 600 of providing pathlength insensitive measurements of blood constituents in a sample using IR spectroscopy. In an operational block 610, the method 600 comprises providing an absorbance spectrum of the sample. In an operational block 620, the method 600 further comprises shifting the absorbance spectrum to zero at an isosbestic wavelength. Water and a protein within the sample have approximately equivalent absorptions at the isosbestic wavelength.
2. The method of clause 1, wherein the wavelength region is at or near an isosbestic wavelength.
3. The method of clause 1, wherein the sample is a biological sample and the substance is a whole blood protein.
4. The method of clause 1, wherein the analyte concentration determination is insensitive to pathlength.
5. The method of clause 1, wherein subtracting the water contribution from the absorbance spectrum comprises:
6. The method of clause 7, wherein subtracting the substance contribution from the absorbance spectrum comprises:
7. The method of clause 1, comprising subtracting a residual interactive component contribution from the absorbance spectrum.
8. The method of clause 7, wherein the residual interactive component comprises components of a boundary layer between water and protein.
9. The method of clause 1, further comprising subtracting a potentially interfering substance contribution from the absorbance spectrum.
10. The method of clause 9, wherein the potentially interfering substance comprises urea.
11. The method of clause 1, further comprising subtracting a glucose contribution from the absorbance spectrum and determining a residual substance concentration in the sample.
12. The method of clause 11, wherein the residual substance comprises lactate.
13. The method of clause 11, wherein the residual substance comprises urea.
14. The method of clause 1, wherein the OD spectrum is fitted with reference glucose spectral data, thereby yielding a measurement of glucose concentration in the sample.
15. The method of clause 14, wherein the absorbance spectrum is fitted with reference glucose spectral data at at least one glucose absorbance maximum.
16. The method of clause 15, wherein the at least one glucose absorbance maximum is at approximately 9. 25 µm.
17. The method of clause 15, wherein the at least one glucose absorbance maximum is at approximately 9.65 µm.
providing an absorbance spectrum of the sample; shifting the absorbance spectrum to zero at an isosbestic wavelength, wherein water and a protein within the sample have approximately equivalent absorptions at the isosbestic wavelength.
A method of measuring concentration of glucose in a fluid sample comprising, in no particular order:
providing a detector that detects radiation emitted from the source, the detection occurring after the radiation has traveled a pathlength, traveling a path length comprising passing at least through the cuvette;
The method of Claim 1, wherein the emitter emits electromagnetic radiation in the infrared range.
The method of Claim 1, wherein the correct reference water absorbance spectra is subtracted from the total sample absorbance data before the correct reference protein absorbance spectra is subtracted from the total sample absorbance data.
The method of Claim 1, wherein the pathlength is determined based on water absorbance for wavelengths between approximately 4.5 and approximately 5 micrometers.
The method of Claim 1, wherein the range of wavelengths comprises more than one wavelength.
The method of Claim 1, wherein the correct water absorbance reference spectrum comprises the absorption rate of water at more than one wavelength for the given pathlength.
The method of Claim 1, wherein the correct water absorbance reference spectrum is determined using an absorbance peak at approximately 4.7 micrometers.
The method of Claim 1, wherein confirmation that the correct water absorbance reference spectrum has been subtracted is obtained by determination that there is zero residual absorbance in the wavelengths between approximately 4.5 and approximately 5 micrometers.
The method of Claim 1, wherein the correct protein absorbance reference spectrum comprises the absorption rate of protein at more than one wavelength for the given pathlength.
The method of Claim 1, wherein the correct protein absorbance reference spectrum is determined using an absorbance peak between approximately 7.0 and approximately 7.2 micrometers.
The method of Claim 1, wherein the correct protein absorbance reference spectrum is determined using an absorbance peak between approximately 7.9 and approximately 8.1 micrometers.
The method of Claim 1, wherein absorbance spectra are obtained using a Fourier-Transform Infrared instrument.
The method of Claim 1, wherein the concentration of glucose is determined using an absorbance peak at approximately 9.25 micrometers.
The method of Claim 1, wherein the concentration of glucose is determined using an absorbance peak at approximately 9.65 micrometers.
A method of measuring concentration of an analyte in a fluid sample comprising, in no particular order:
The method of Claim 15, wherein the analyte is Glucose.
The method of Claim 15, wherein the sample container is a cuvette.
The method of Claim 15, wherein the emitter emits electromagnetic radiation in the infrared range.
The method of Claim 15, wherein the pathlength is determined using a fringe pattern of the fluid container when the container is empty.
The method of Claim 15, wherein the pathlength is determined by measuring the absorbance of the reference fluid.
The method of Claim 21, wherein the pathlength determination is made both before and after composite sample data has been obtained.
The method of Claim 21, wherein the reference fluid is water.
The method of Claim 21, wherein the reference fluid is saline solution.
The method of Claim 15, wherein the pathlength is determined based on water absorbance for a wavelength in the range of approximately 4.5 to approximately 5 micrometers,
The method of Claim 15, wherein the range of wavelengths comprises more than one wavelength.
The method of Claim 15, wherein the range of wavelengths comprises at least one discreet wavelength.
The method of Claim 15, wherein the correct water absorbance reference spectrum comprises the absorption rate of water at more than one wavelength for the given pathlength.
The method of Claim 15, wherein the correct water absorbance reference spectrum comprises at least one absorbance value at or near a reference water wavelength.
The method of Claim 15, wherein the correct water absorbance reference spectrum is determined using an absorbance peak at approximately 4.7 micrometers.
The method of Claim 15, wherein confirmation that the correct water absorbance reference spectrum has been subtracted is obtained by determination that there is zero residual absorbance in the wavelengths between approximately 4.5 and approximately 5 micrometers.
The method of Claim 15, wherein the correct protein absorbance reference spectrum comprises the absorption rate of protein at more than one wavelength for the given pathlength.
The method of Claim 15, wherein the correct protein absorbance reference spectrum comprises at least one absorbance value at or near a reference protein wavelength.
The method of Claim 15, wherein the correct protein absorbance reference spectrum is determined using an absorbance peak between approximately 7.0 and approximately 72 micrometers.
The method of Claim 15, wherein the correct protein absorbance reference spectrum is determined using an absorbance peak between approximately 7.9 and approximately 8.1 micrometers.
The method of Claim 15, wherein absorbance spectra are obtained using a Fourier-Transform Infrared instrument.
The method of Claim 38, wherein the concentration of the analyte is determined using an absorbance peak at approximately 9.25 micrometers.
The method of Claim 38, wherein the concentration of the analyte is determined using an absorbance peak at approximately 9.65 micrometers.
The method of Claim 41, wherein at least one of the reference water wavelengths is approximately 4.7 micrometers.
The method of Claim 41, wherein at least one of the reference protein wavelengths is approximately 7.1 micrometers.
The method of Claim 41, wherein at least one of the reference protein wavelengths is approximately 8.0 micrometers.
EP07015609A 2001-12-14 2002-12-12 Spectroscopic method of determining an analyte concentration in a sample Withdrawn EP1850114A1 (en)
EP20020794266 EP1454126B1 (en) 2001-12-14 2002-12-12 Spectroscopic method of determining an analyte concentration in a sample
EP20020794266 Division EP1454126B1 (en) 2001-12-14 2002-12-12 Spectroscopic method of determining an analyte concentration in a sample
EP1850114A1 true EP1850114A1 (en) 2007-10-31
ID=38529847
EP07015609A Withdrawn EP1850114A1 (en) 2001-12-14 2002-12-12 Spectroscopic method of determining an analyte concentration in a sample
EP (1) EP1850114A1 (en)
GB2480153A (en) * 2010-05-05 2011-11-09 Valentine John Rossiter Highly inert fluid-handling optical system
2002-12-12 EP EP07015609A patent/EP1850114A1/en not_active Withdrawn
KEN-ICHIRO KAJIWARA: "SPECTROSCOPIC QUANTITATIVE ANALYSIS OF BLOOD GLUCOSE BY FOURIER TRANSFORM INFRARED SPECTROSCOPY WITH AN ATTENUATED TOTAL REFLECTIONPRISM", MEDICAL PROGRESS THROUGH TECHNOLOGY, SPRINGER VERLAG. BERLIN, DE, vol. 18, no. 3, January 1992 (1992-01-01), pages 181 - 189, XP000331119, ISSN: 0047-6552 *
US8140140B2 (en) 2012-03-20 Analyte detection system for multiple analytes
US7860543B2 (en) 2010-12-28 Analyte detection system with reduced sample volume
Ref document number: 1454126
Inventor name: BRAIG, JAMES R.
Inventor name: HARTSTEIN, PHILIP