U.S. patent application number 14/855005 was filed with the patent office on 2016-01-07 for method and assembly for determining the temperature of a test sensor.
The applicant listed for this patent is Bayer HealthCare LLC. Invention is credited to Paul M. Ripley, Hoi-Cheong Steve Sun.
Application Number | 20160003749 14/855005 |
Document ID | / |
Family ID | 41528748 |
Filed Date | 2016-01-07 |
United States Patent
Application |
20160003749 |
Kind Code |
A1 |
Sun; Hoi-Cheong Steve ; et
al. |
January 7, 2016 |
METHOD AND ASSEMBLY FOR DETERMINING THE TEMPERATURE OF A TEST
SENSOR
Abstract
An assembly determines an analyte concentration in a sample of
body fluid. The assembly includes a test sensor having a
fluid-receiving area for receiving a sample of body fluid, where
the fluid-receiving area contains a reagent that produces a
measurable reaction with an analyte in the sample. The assembly
also includes a meter having a port or opening configured to
receive the test sensor; a measurement system configured to
determine a measurement of the reaction between the reagent and the
analyte; and a temperature-measuring system configured to determine
a measurement of the test-sensor temperature when the test sensor
is received into the opening. The meter determines a concentration
of the analyte in the sample according to the measurement of the
reaction and the measurement of the test-sensor temperature.
Inventors: |
Sun; Hoi-Cheong Steve;
(Tampa, FL) ; Ripley; Paul M.; (Nanuet,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bayer HealthCare LLC |
Whippany |
NJ |
US |
|
|
Family ID: |
41528748 |
Appl. No.: |
14/855005 |
Filed: |
September 15, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14227994 |
Mar 27, 2014 |
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14855005 |
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12580081 |
Oct 15, 2009 |
8709822 |
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14227994 |
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61105806 |
Dec 18, 2008 |
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Current U.S.
Class: |
422/82.05 |
Current CPC
Class: |
G01N 33/521 20130101;
G01N 21/4788 20130101; G01N 21/8483 20130101; G01N 25/20 20130101;
G01N 2201/1211 20130101; G01N 21/251 20130101; G01N 21/78
20130101 |
International
Class: |
G01N 21/78 20060101
G01N021/78; G01N 21/47 20060101 G01N021/47; G01N 25/20 20060101
G01N025/20; G01N 21/25 20060101 G01N021/25 |
Claims
1-24. (canceled)
25. A test sensor for determining an analyte concentration in a
fluid sample, comprising: a fluid-receiving area for receiving a
fluid sample, the fluid-receiving area including a reagent that
produces a measurable reaction with an analyte in the sample, the
test sensor having a test-sensor temperature and the reagent having
a reagent temperature; and a temperature-dependent element disposed
along a surface of the test sensor, wherein the test sensor is
configured to be received in the opening of a meter, the
temperature-dependent element being disposed along the surface of
the test sensor so that the temperature-dependent element can be
detected inside the meter when the test sensor is received into the
opening, the meter being configured to determine a measurement of
the reaction between the reagent and the analyte, the meter
including a temperature-measuring system configured to determine a
measurement of the test-sensor temperature from the
temperature-dependent element when the temperature-dependent
element is inside the meter, the meter being configured to
determine a concentration of the analyte in the sample using the
measurement of the reaction and the measurement of the test-sensor
temperature.
26. The test sensor of claim 25, wherein the fluid-receiving area
and the temperature dependent element are disposed substantially at
opposing ends of the test sensor.
27. The test sensor of claim 25, wherein the temperature-dependent
element includes a grating, the grating including a series of
parallel linear structures equally separated by a distance that
changes in response to temperature, and the temperature-measuring
system includes a light source and a light detector, the grating
being configured to receive incident light directed from the light
source, the detector being configured to receive, from the grating
disposed inside the meter, diffracted light that changes according
to changes in the distance separating the linear structures of the
grating, the temperature-measuring system determining the
measurement of the test-sensor temperature according to the
diffracted light.
28. The test sensor of claim 27, wherein the light source includes
a laser of a fixed wavelength directed to the grating, and the
detector receives the diffracted light from the grating according
to an angle, the angle indicating the distance separating the
linear structures of the grating, and the temperature-measuring
system determining the measurement of the test-sensor temperature
according to the angle.
29. The test sensor of claim 28, wherein the fixed wavelength
ranges from approximately 450 nm to 1800 nm.
30. The test sensor of claim 27, wherein the light source generates
white light and directs the white light to the grating, and the
detector receives the diffracted light from the grating, the
diffracted light including red, green, and blue (RGB) components,
the RGB components in the diffracted light indicating the distance
separating the linear structures of the grating, and the
temperature-measuring system determining the measurement of the
test-sensor temperature according to the angle.
31. The test sensor of claim 25, wherein the grating is rolled into
the surface of the test sensor.
32. The test sensor of claim 25, wherein the grating is engraved
into the surface of the test sensor with laser processing.
33. The test sensor of claim 25, wherein the grating may be formed
from a separate material and applied to the test sensor.
34. The test sensor of claim 33, wherein the separate material is
applied to the surface of the test sensor by deposition.
35. The test sensor of claim 25, wherein the temperature-dependent
element includes a polarizing material disposed along a surface of
the test sensor, the polarizing material causing a degree of
polarization of light reflected from the polarizing material, the
polarizing material having a structure that changes in response to
temperature and changes the degree of polarization, and the
temperature-measuring system includes a light source and a light
detector, the polarizing material being configured to receive
incident light directed from the light source, and the detector
being configured to receive, from the polarizing material disposed
inside the meter, an amount of reflected light that changes
according to the degree of polarization, the temperature-measuring
system determining the measurement of the test-sensor temperature
according to the amount of reflected light received by the
detector.
36. The test sensor of claim 35, wherein the light source is a
laser of a fixed wavelength directed to the polarizing
material.
37. The test sensor of claim 36, wherein the fixed wavelength
ranges from approximately 450 nm to 1800 nm.
38. An assembly for determining an analyte concentration of a fluid
sample, the assembly comprising: a test sensor comprising a
fluid-receiving area for receiving a fluid sample, the
fluid-receiving area including a reagent that produces a measurable
reaction with an analyte in the sample, the test sensor having a
test-sensor temperature and the reagent having a reagent
temperature, the test sensor including a temperature-dependent
element disposed along a surface of the sensor; and a meter
including (i) an opening configured to receive the test sensor
inside the meter, the temperature-dependent element of the test
sensor being disposed along the surface of the test sensor so that
the temperature-dependent element can be detected inside the meter
when the test sensor is received into the opening, (ii) a
measurement system configured to determine a measurement of the
reaction between the reagent and the analyte, and (iii) a
temperature-measuring system configured to determine a measurement
of the test-sensor temperature from the temperature dependent
element when the temperature-dependent element is inside the meter,
the meter further being configured to determine a concentration of
the analyte in the fluid sample using the measurement of the
reaction and the measurement of the test-sensor temperature.
39. The assembly of claim 38, wherein the fluid-receiving area and
the temperature-dependent element are disposed substantially at
opposing ends of the test sensor.
40. The assembly of claim 38, wherein the temperature-dependent
element of the test sensor includes a grating, the grating
including a series of parallel linear structures equally separated
by a distance that changes in response to temperature, and the
temperature-measuring system of the meter includes a light source
and a light detector, the grating being configured to receive
incident light directed from the light source, the detector being
configured to receive, from the grating disposed inside the meter,
diffracted light that changes according to changes in the distance
separating the linear structures of the grating, the
temperature-measuring system determining the measurement of the
test-sensor temperature according to the diffracted light.
41. The assembly of claim 40, wherein the light source includes a
laser of a fixed wavelength directed to the grating, and the
detector receives the diffracted light from the grating according
to an angle, the angle indicating the distance separating the
linear structures of the grating, and the temperature-measuring
system determining the measurement of the test-sensor temperature
according to the angle.
42. The assembly of claim 41, wherein the fixed wavelength ranges
from approximately 450 nm to 1800 nm.
43. The assembly of claim 40, wherein the light source generates
white light and directs the white light to the grating, and the
detector receives the diffracted light from the grating, the
diffracted light including red, green, and blue (RGB) components,
the RGB components in the diffracted light indicating the distance
separating the linear structures of the grating, and the
temperature-measuring system determining the measurement of the
test-sensor temperature according to the angle.
44. The assembly of claim 38, wherein the grating may be formed
from a separate material and applied to the test sensor.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 61/105,806, having a filing date of Dec. 18, 2008,
the contents of which are incorporated entirely herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention generally relates to a method and
assembly for determining an analyte concentration in a sample of
body fluid collected on a test sensor. More specifically, the
present invention generally relates to a method and assembly for
measuring the temperature of the test sensor to determine the
temperature of a reagent reacting with the analyte and to achieve
an accurate determination of the analyte concentration based on the
reaction with the reagent.
BACKGROUND OF THE INVENTION
[0003] The quantitative determination of analytes in body fluids is
of great importance in the diagnoses and maintenance of certain
physiological abnormalities. For example, lactate, cholesterol and
bilirubin are monitored in certain individuals. In particular, it
is important that individuals with diabetes frequently check the
glucose level in their body fluids to regulate the glucose intake
in their diets. The results of such tests can be used to determine
what, if any, insulin or other medication needs to be administered.
In one type of blood-glucose testing system, test sensors are used
to test a sample of blood.
[0004] A test sensor contains biosensing or reagent material that
reacts with, for example, blood glucose. For example, the testing
end of the sensor may be adapted to be placed into contact with the
fluid being tested (e.g., blood) that has accumulated on a person's
finger after the finger has been pricked. The fluid may be drawn
into a capillary channel that extends in the sensor from the
testing end to the reagent material by capillary action so that a
sufficient amount of fluid to be tested is drawn into the sensor.
The tests are typically performed using a meter that receives the
test sensor into a test-sensor opening and applies optical or
electrochemical testing methods.
[0005] The accuracy of such testing methods however may be affected
by the temperature of the test sensor. For example, the result of
the chemical reaction between blood glucose and a reagent on a test
sensor may vary at different temperatures. To achieve an accurate
reading, the actual measurement is corrected based on the actual
sensor temperature, taken right before the reaction begins. The
conventional way to measure the test sensor temperature involves
reading a resistive value from a thermistor placed near the
test-sensor opening. The thermistor resistance recalculates the
chemical reaction result. This correction method is based on an
assumption that a sensor temperature is the same as the thermistor
temperature placed near the test-sensor opening. In reality,
however, the thermistor, which is typically located on a printed
circuit board, actually provides the temperature of the meter.
Because the temperature of the meter can be very different from the
test sensor temperature, the analyte measurement may be
inaccurate.
[0006] As a result, it would be desirable to have a method and
assembly that accurately measures and accounts for the temperature
of the test sensor for achieving an accurate analyte
measurement.
SUMMARY OF THE INVENTION
[0007] Reagents that are used to measure analyte concentration in a
sample of body fluid may be sensitive to changes in temperature. In
other words, the magnitude of the reaction between the reagent and
the analyte may depend on the temperature of the reagent. As a
result, any calculation of the analyte concentration in the sample
based on the reaction may vary with the temperature of the reagent.
Accordingly, to achieve a more accurate measurement of the analyte
concentration, embodiments of the present invention also determine
the temperature of the reagent. The temperature of the reagent is
used by an algorithm which determines the analyte concentration.
Embodiments may determine the reagent temperature by measuring the
temperature of a test sensor that holds the reagent in a
fluid-receiving area for reaction with a collected sample. In
particular, these embodiments measure the test-sensor temperature
while the area of the test sensor being measured is in equilibrium
with the reagent temperature.
[0008] One embodiment provides an assembly for determining an
analyte concentration in a sample of body fluid. The assembly
includes a test sensor having a fluid-receiving area for receiving
a sample of body fluid, where the fluid-receiving area contains a
reagent that produces a measurable reaction with an analyte in the
sample. The test sensor has a grating disposed along a surface of
the test sensor, the grating including a series of parallel linear
structures equally separated by a distance that changes in response
to temperature. The assembly also includes a meter having a port or
opening configured to receive the test sensor; a measurement system
configured to determine a measurement of the reaction between the
reagent and the analyte; and a temperature-measuring system
configured to determine a measurement of the test-sensor
temperature when the test sensor is received into the opening. The
temperature-measuring system includes a light source and a light
detector, the light source being configured to direct incident
light to the grating, and the detector being configured to receive,
from the grating, diffracted light that changes according to
changes in the distance separating the linear structures of the
grating. The temperature-measuring system determines the
measurement of the test-sensor temperature according to the
diffracted light. The meter determines a concentration of the
analyte in the sample according to the measurement of the reaction
and the measurement of the test-sensor temperature.
[0009] In one example, the light source includes a laser of a fixed
wavelength directed to the grating. The detector receives the
diffracted light from the grating according to an angle. The angle
indicates the distance separating the linear structures of the
grating, and the temperature-measuring system determines the
measurement of the test-sensor temperature according to the
angle.
[0010] In another example, the light source generates white light
and directs the white light to the grating. The detector receives
the diffracted light from the grating. The diffracted light
includes red, green, and blue (RGB) components. The RGB components
in the diffracted light indicates the distance separating the
linear structures of the grating, and the temperature-measuring
system determines the measurement of the test-sensor temperature
according to the angle.
[0011] Another embodiment provides an assembly for determining an
analyte concentration in a sample of body fluid. The assembly
includes a test sensor having a fluid-receiving area for receiving
a sample of body fluid, where the fluid-receiving area contains a
reagent that produces a measurable reaction with an analyte in the
sample. The test sensor has a polarizing material disposed along a
surface of the test sensor. The polarizing material causes a degree
of polarization of light reflected from the polarizing material.
The polarizing material has a structure that changes in response to
temperature and changes the degree of polarization. The assembly
also includes a meter having a port or opening configured to
receive the test sensor; a measurement system configured to
determine a measurement of the reaction between the reagent and the
analyte; and a temperature-measuring system configured to determine
a measurement of the test-sensor temperature when the test sensor
is received into the opening. The temperature-measuring system
includes a light source and a light detector, the light source
being configured to direct incident light to the polarizing
material, and the detector being configured to receive, from the
polarizing material, an amount of reflected light that changes
according to the degree of polarization. The temperature-measuring
system determining the measurement of the test-sensor temperature
according to the amount of reflected light received by the
detector. The meter determines a concentration of the analyte in
the sample according to the measurement of the reaction and the
measurement of the test-sensor temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates a general diagnostic system, including a
test sensor and a meter, according to an embodiment of the present
invention.
[0013] FIG. 2 illustrates the embodiment of FIG. 1 with the test
sensor inserted into the meter.
[0014] FIG. 3A illustrates a partial plan view of a meter according
to an embodiment of the present invention.
[0015] FIG. 3B illustrates an enlarged transparent partial view of
the meter of FIG. 3A.
[0016] FIG. 3C illustrates an internal side view of the meter of
FIG. 3A.
[0017] FIG. 3D illustrates yet another internal view of the meter
of FIG. 3A.
[0018] FIG. 3E illustrates yet another internal view of the meter
of FIG. 3A.
[0019] FIG. 3F illustrates an example processing system for the
meter of FIG. 3A.
[0020] FIG. 4A illustrates a thermopile sensor and a thermistor
that may be used by an embodiment of the present invention.
[0021] FIG. 4B illustrates a bottom view of the thermopile sensor
and the thermistor of FIG. 4A.
[0022] FIG. 5 illustrates a configuration for an optical-sensing
system that may be used by an embodiment of the present
invention.
[0023] FIG. 6 illustrates a view of a test sensor employing a
thermochromic liquid crystals according to an embodiment of the
present invention.
[0024] FIG. 7 illustrates molecular changes of the thermochromic
liquid crystal with temperature.
[0025] FIG. 8 illustrates the range of the color of the
thermochromic liquid crystal depending on temperature.
[0026] FIG. 9 illustrates a graph of temperature vs. time and
optical intensity (RGB) vs. time from an example experimental
setup.
[0027] FIG. 10 illustrates a graph of temperature vs. color
intensity (RGB) converted from the data of the graph of FIG. 9.
[0028] FIG. 11A illustrates a subroutine for optical processing to
convert RGB data into temperature data.
[0029] FIG. 11B illustrates a general algorithm to process optical
data to convert RGB data into temperature data.
[0030] FIG. 12 illustrates a graph of temperature vs. time and
optical intensity (RGB) vs. time for 20.degree. C. to 40.degree. C.
temperature tests.
[0031] FIG. 13 illustrates a graph of temperature vs. color
intensity (RGB) converted from the data of the graph of FIG.
12.
[0032] FIG. 14 illustrates TCLC-based temperature and thermocouple
data corresponding to the data of FIGS. 12 and 13.
[0033] FIG. 15 illustrates a "sliced-pie TCLC configuration" for
measuring temperatures with an array of TCLC materials according to
aspects of the present invention.
[0034] FIG. 16 illustrates a configuration for another
optical-sensing system that may be used by an embodiment of the
present invention.
[0035] FIG. 17 illustrates a configuration for a further
optical-sensing system that may be used by an embodiment of the
present invention.
[0036] FIG. 18 illustrates a configuration for yet another
optical-sensing system that may be used by an embodiment of the
present invention.
[0037] FIG. 19 illustrates a system for calibrating a device, such
as a CGM sensor, with a controller having a temperature-measuring
system according to aspects of the present invention.
[0038] While the invention is susceptible to various modifications
and alternative forms, specific embodiments are shown by way of
example in the drawings and are described in detail herein. It
should be understood, however, that the invention is not intended
to be limited to the particular forms disclosed. Rather, the
invention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS
[0039] Aspects of the present invention provide methods and
assemblies for measuring the temperature of a reagent on a test
sensor used to collect a sample of body fluid. The reagent reacts
with an analyte in the sample of body fluid and the level of
reaction may be measured to determine the concentration of analyte
in the sample. The level of reaction may be affected by changes in
temperature of the reagent. By measuring the temperature of the
reagent, aspects of the present invention may account for the
reagent's sensitivity to temperature and thus obtain a more
accurate calculation of the concentration of analyte in the
sample.
[0040] Referring to FIG. 1, a diagnostic system 10 with a test
sensor 100 and a meter 200 is illustrated. The test sensor 100 is
configured to receive a fluid sample and is analyzed using the
meter 200. Analytes that may be analyzed include glucose, lipid
profiles (e.g., cholesterol, triglycerides, LDL and HDL),
microalbumin, hemoglobin A.sub.1C, fructose, lactate, or bilirubin.
It is contemplated that other analyte concentrations may be
determined. The analytes may be in, for example, a whole blood
sample, a blood serum sample, a blood plasma sample, other body
fluids like ISF (interstitial fluid) and urine, and non-body
fluids. As used within this application, the term "concentration"
refers to an analyte concentration, activity (e.g., enzymes and
electrolytes), titers (e.g., antibodies), or any other measure
concentration used to measure the desired analyte.
[0041] As shown in FIG. 1, the test sensor 100 includes a body 105
having a fluid-receiving area 110 for receiving a sample of body
fluid. For example, a user may employ a lancet or a lancing device
to pierce a finger or other area of the body to produce the blood
sample at the skin surface. The user may then collect this blood
sample by placing an opening 107 of the test sensor 100 into
contact with the sample. The blood sample may flow from the opening
107 to the fluid-receiving area 110 via a capillary channel 108, as
generally depicted in the embodiment of FIG. 1. The fluid-receiving
area 110 may contain a reagent 115 which reacts with the sample to
indicate the concentration of an analyte in the sample. The test
sensor 100 also has a meter-contact area 112 which is received by
the meter 200 as described in detail further below.
[0042] The test sensor 100 may be an electrochemical test sensor.
An electrochemical test sensor typically includes a plurality of
electrodes and a fluid-receiving area that contains an enzyme. The
fluid-receiving area includes a reagent for converting an analyte
of interest (e.g., glucose) in a fluid sample (e.g., blood) into a
chemical species that is electrochemically measurable, in terms of
the electrical current it produces, by the components of the
electrode pattern. The reagent typically contains an enzyme such
as, for example, glucose oxidase, which reacts with the analyte and
with an electron acceptor such as a ferricyanide salt to produce an
electrochemically measurable species that can be detected by the
electrodes. It is contemplated that other enzymes may be used to
react with glucose such as glucose dehydrogenase. In general, the
enzyme is selected to react with the desired analyte or analytes to
be tested so as to assist in determining an analyte concentration
of a fluid sample. If the concentration of another analyte is to be
determined, an appropriate enzyme is selected to react with the
analyte. Examples of electrochemical test sensors, including their
operation, may be found in, for example, U.S. Pat. No. 6,531,040
assigned to Bayer Corporation. It is contemplated, however, that
other electrochemical test sensors may be employed.
[0043] Alternatively, the test sensor 100 may be an optical test
sensor. Optical test sensor systems may use techniques such as, for
example, transmission spectroscopy, diffuse reflectance, or
fluorescence spectroscopy for measuring the analyte concentration.
An indicator reagent system and an analyte in a sample of body
fluid are reacted to produce a chromatic reaction, as the reaction
between the reagent and analyte causes the sample to change color.
The degree of color change is indicative of the analyte
concentration in the body fluid. The color change of the sample is
evaluated to measure the absorbance level of the transmitted light.
Transmission spectroscopy is described in, for example, U.S. Pat.
No. 5,866,349. Diffuse reflectance and fluorescence spectroscopy
are described in, for example, U.S. Pat. No. 5,518,689 (titled
"Diffuse Light Reflectance Read Head"), U.S. Pat. No. 5,611,999
(titled "Diffuse Light Reflectance Read Head"), and U.S. Pat. No.
5,194,393 (titled "Optical Biosensor and Method of Use").
[0044] As further illustrated in FIG. 1, the meter 200 includes a
body portion 205 with a test sensor opening 210, which includes a
connector for receiving and/or holding a test sensor 100. The meter
200 also includes a measurement system 220 for measuring the
concentration of analyte for the sample in fluid-receiving area
110. For example, the measurement system 220 may include contacts
for the electrodes to detect the electrochemical reaction for an
electrochemical test sensor. Alternatively, the measurement system
220 may include an optical detector to detect the chromatic
reaction for an optical test sensor. To process information from
the measurement system 220 and to generally control the operation
of the meter 200, the meter 200 may employ at least one processing
system 230, which may execute programmed instructions according to
a measurement algorithm. Data processed by the processing system
230 may be stored in a conventional memory device 235. Furthermore,
the meter may have a user interface 240 which includes a display
245, which, for example, may be a liquid-crystal display.
Pushbuttons, a scroll wheel, touch screens, or any combination
thereof, may also be provided as a part of the user interface 240
to allow a user to interact with the meter 200. The display 245
typically shows information regarding the testing procedure and/or
information in response to signals input by the user. The result of
the testing may also be announced audibly, by, for example, using a
speaker.
[0045] In general operation, a user removes a test sensor 100 from
a package, such as a container, at time t.sub.0. The user then
inserts the test sensor 100 into the test-sensor opening 210 at
time t.sub.1, as shown in FIG. 2. Upon insertion of the test sensor
100 at time t.sub.1, the meter 200 is activated, i.e. wakes up, to
begin a predefined testing procedure according to one method. In
particular, a signal is sent from the test-sensor opening 210 to
wake up the measurement system 220. This signal, for example, may
be mechanically or electrically generated. The user then places the
test sensor 100 at time t.sub.s into contact with a sample of body
fluid, which is received into the fluid-receiving area 110. The
sample then reacts with the reagent 115, and the measurement system
220 measures the level of reaction. The processing system 230
receives information on the reaction, e.g. in the form of a
electrical signal, and determines the amount of analyte
concentration in the sample according to the measurement algorithm.
The results of this measurement may then be recorded in memory
device 235 and/or displayed to the user via the display 245.
[0046] Diagnostic systems, such as blood-glucose testing systems,
typically calculate the actual glucose value based on a measured
output and the known reactivity of the reagent-sensing element
(e.g., test sensor 100) used to perform the test. Calibration
information is generally used to compensate for different
characteristics of test sensors, which will vary on a
batch-to-batch basis. The calibration information may be, for
example, the lot specific reagent calibration information for the
test sensor. The calibration information may be in the form of a
calibration code. Selected information associated with the test
sensor (which may vary on a batch-to-batch basis) is tested to
determine the calibration information to be used in association
with the meter. The reactivity or lot-calibration information of
the test sensor may be provided on a calibration circuit that is
associated with the sensor package or the test sensor. This
calibration circuit may be inserted by the end user. In other
cases, the calibration is automatically done using an
auto-calibration circuit via a label on the sensor package or the
test sensor. In these cases, calibration is transparent to the end
user and does not require that the end user insert a calibration
circuit into the meter or enter coding information. Some
embodiments of the present invention may provide either a manual-
or auto-calibrating diagnostic system. In the example shown in FIG.
1, the diagnostic system 10 is auto-calibrating, so the test sensor
100 may include an auto-calibration information area 120, which may
include a label, at the meter-contact area 112.
[0047] As discussed previously, the temperature of the reagent on
the test sensor 100 may affect the accuracy of the concentration of
analyte calculated by the meter 200, as the level of reaction
between the analyte and the reagent 115 may be dependent on the
temperature of the reagent 115. As such, some embodiments of the
present invention determine a temperature for the reagent 115 and
use this calculated temperature to produce a more accurate
measurement of the analyte concentration. In particular, the meter
200 has a temperature-measuring system 250 and the processing
system 230 uses this calculated temperature from the
temperature-measuring system 250 as a variable input for a
measurement algorithm.
[0048] In operation, when a test sensor 100 is inserted at time
t.sub.1 into the test-sensor opening 210 of the meter, the
temperature of the test sensor 100 is also measured with the
temperature-measuring system 250. Although the system 250 may
actually measure the temperature of the test sensor 100, i.e., the
meter-contact area 112, instead of the temperature of the reagent
115, the temperatures of the test sensor 100 and the reagent 115
are generally at equilibrium with the ambient temperature when the
test sensor 100 is inserted into the test-sensor opening 210 at
time t.sub.1. As shown in FIG. 2, when the test sensor 100 is
inserted into the test-sensor opening 210, the meter-contact area
112 is positioned in the test-sensor opening 210, but the
fluid-receiving area 110 may be positioned distally from the meter
200. As such, the meter-contact area 112 may be heated by sources
of heat in the meter 200, such as components receiving power from a
power source. However, the fluid-receiving area 110 and the reagent
115 may be sufficiently spaced from the sources of heat to remain
substantially at ambient temperature. Thus, determining the ambient
temperature provides a useful estimate of the temperature of the
reagent 115, which is used as a factor in determining analyte
concentration. It is noted that for a brief time, the temperature
of the fluid-receiving area 110 may increase at time t.sub.s when
it receives the fluid sample, which may retain some heat from the
body. It has been determined that for a short time period, e.g.,
approximately 0.5 seconds to approximately 5 seconds, after the
test sensor 100 has been inserted into the test-sensor opening 210
at time t.sub.1, the ambient temperature can still be determined
from the meter-contact area 112 before the temperature of the area
112 increases due to heat from the meter 200 or decreases due to
cooling from the meter 200. The time period for determining the
ambient temperature from the meter-contact area 112 may vary from
the time that the test sensor is inserted, e.g., approximately 0.5
seconds to approximately 5 seconds, depending on factors, such as
the type of meter being used, etc. It is understood that the time
range provided here, i.e., approximately 0.5 seconds to
approximately 5 seconds, is provided as an example and that other
time periods may be appropriate. Other such factors are discussed
further below. Accordingly, some embodiments of the present
invention may measure the temperature of area 112 at time t.sub.1
when the effects of heat or cooling from the meter 200 are still at
a minimum.
[0049] Although some embodiments may measure the temperature of
area 112 at time t.sub.1 described above, other embodiments may
measure the temperature at other times. Even if the effects of heat
or cooling from the meter 200 have already changed the temperature
of the area 112 at the time of measurement, the temperature of the
area 112 prior to the effects of heat or cooling may be determined
by applying an algorithm to the measurement. For example, the
temperature as a function of time, i.e., a temperature-time curve,
may be applied to extrapolate backwards from the measurement to
determine a temperature at time t.sub.1, before the actual
measurement time.
[0050] As shown in FIG. 2 and FIGS. 3A-E, the temperature-measuring
system 250 is positioned in the test-sensor opening 210 of the
meter body 205, such that the temperature-measuring system 250 may
be positioned in proximity to the test sensor 100 when it is
inserted into the test-sensor opening 210. In the embodiment
illustrated by FIGS. 3A-E, the temperature-measuring system 250
includes a thermopile sensor 250A disposed at a position 251 within
the test-sensor opening 210, for example on a printed circuit board
231.
[0051] Although some embodiments may include a
temperature-measuring system 250 disposed at a position 251 within
the test-sensor opening 210, a temperature-measuring system 250 may
be disposed at other areas to allow temperature measurement of test
sensor 100. For example, the temperature-measuring system 250 may
be positioned on a structure, such as an arm, that extends
outwardly from the meter body 205 to measure an area of the test
sensor 100 that is positioned outside the test-sensor opening 210
when the test sensor 100 is inserted into the test-sensor opening
210. The structure may extend permanently from the meter body 205
or may be operated manually or triggered automatically to extend or
swing out into an appropriate position for measuring an area of the
test sensor 100. Moreover, other embodiments may include more than
one structure disposed anywhere relative to the meter body 205 for
measuring more than one area of the test sensor 100. Temperature
measurements from more than one area may provide a more accurate
determination of the temperature for the reagent 115. For example,
unlike the configuration of FIG. 3E, the test sensor 100 may be
inserted transversely, rather then longitudinally, into a
test-sensor opening 210, so that more than one area along the test
sensor 100 may be accessed to obtain temperature measurements.
[0052] In general, all materials at temperatures above absolute
zero continuously emit energy. Infrared radiation is part of the
electromagnetic spectrum and occupies frequencies between visible
light and radio waves. The infrared (IR) part of the spectrum spans
wavelengths from about 0.7 micrometers to about 1000 micrometers.
The wave band usually used for temperature measurement is from
about 0.7 to about 20 micrometers. The thermopile sensor 250A
measures the actual sensor strip temperature by using blackbody
radiation emitted from the test sensor 100. By knowing the amount
of infrared energy emitted by the test sensor 100 and its
emissivity, the actual temperature of the test sensor 100 can be
determined. In particular, the thermopile sensor 250A may generate
a voltage proportional to incident infrared radiation. Because the
temperature of a surface of the test sensor 250A is related to the
incident infrared radiation, the temperature of the surface can be
determined from the thermopile sensor 250A.
[0053] When the test sensor 100 is received into the test-sensor
opening 210, the position 251 of the thermopile sensor 250A is
proximate, or substantially adjacent, to the test sensor 100. The
position 251 ensures that the infrared radiation detected by the
thermopile sensor 250A comes substantially from the test sensor
100. In other words, the thermopile sensor 250A may be positioned
to minimize the effect of light from external sources, e.g.,
ambient light, on the readings of the thermopile sensor 250A. While
FIG. 3E, for example, show the thermopile sensor 250A below the
test sensor 100, it is understood that the thermopile sensor may be
positioned in other appropriate positions relative to the test
sensor.
[0054] FIG. 3F illustrates aspects of a processing system 230 that
may be employed for implementing the thermopile sensor 250A in the
meter 200. First, an output electrical signal from the thermopile
sensor 250A is received by an analog amplifier 230A. The amplified
analog signal from the analog amplifier 230A is passed to an
analog-to-digital converter 230C via an analog filter 230B. The
analog-to-digital converter 230C digitizes the amplified analog
signal, which may subsequently be filtered by a digital filter
230D. The digital signal is then transmitted to a microcontroller
230E. The microcontroller 230E calculates the temperature of the
test sensor 100 based on the magnitude of the output electrical
signal from the thermopile sensor 250A and the calculated
temperature is employed to correct the initial blood glucose
measurement from the measurement system 220. For some embodiments,
it is contemplated that the analog filter 230B, the
analog-to-digital converter 230C, and the digital filter 230D may
be incorporated into the microcontroller 230E. In some embodiments,
the analog filter 230B and the analog-to-digital converter 230C may
be integrated into an application-specific integrated circuit
(ASIC). In further embodiments, a memory, such as an EEPROM, may be
employed to store calibration data and the like. Moreover, it is
further contemplated that in some embodiments the analog filter
230B and the digital filter 230D may be optional. It is also noted
that although the thermopile sensor 250A in FIG. 3F is positioned
opposite from the electrical contacts 221 that receive the test
sensor electrodes, other embodiments may position the thermopile
sensor to be on the same side of the test sensor.
[0055] FIGS. 4A and 4B illustrate a typical thermopile sensor 250A,
which includes a series of thermal elements hermetically sealed in
a metal housing 255A. In particular, the thermopile sensor 250A may
include an optical filter 257A and an absorbing area 258A. It is
contemplated that the thermopile sensor 250A may be housed in a
variety of TO housings or surface mount device housings. The time
constant for the thermopile sensor 250A is of the order of 100 ms
or less, which corresponds operationally with diagnostic systems 10
which have typical test times of the order of approximately 5
seconds. In general, the thermopile sensor 250A provides sufficient
sensitivity, a small temperature coefficient of sensitivity, as
well as high reproducibility and reliability.
[0056] As illustrated in FIGS. 4A and 4B, the temperature-measuring
system 250 may optionally include an additional reference
temperature sensor 260A, such as a sensor, thermistor,
semiconductor temperature sensor, or the like. This reference
temperature resistor, or thermistor, 260A may also be included in
the housing 255A. As such, the temperature-measuring system 250
shown in FIGS. 3A-F can provide the temperature of the test sensor
100 and the reference temperature of the meter body 205 as variable
inputs for the measurement algorithm run by the processing system
230. Accordingly, the temperature-measuring system 250 of FIGS. 4A
and 4B has two pins, e.g. pins 1 and 3, corresponding to the
thermopile sensor 250A and two pins, e.g. pins 2 and 4,
corresponding to the thermistor 260A. Thus, the meter 200 measures
the voltage across the pins 1 and 3, which indicates the amount of
infrared radiation associated with the temperature of the test
sensor 200. In addition, the meter measures the resistance across
pins 2 and 4, which indicates the temperature of the meter body
205. It is contemplated that other types of contact structures,
such as pads, may be employed, and embodiments are not limited to
the use of the pins shown in FIGS. 4A and 4B.
[0057] For example, the meter 200 may be equipped with a Heimann
HMS Z11-F5.5 Ultrasmall Thermopile Sensor (Heimann Sensor GmbH,
Dresden, Germany), which provides a Complementary Metal Oxide
Semiconductor (CMOS) compatible sensor chip plus a thermistor
reference chip. The HMS Z11-F5.5 is 3.55 mm in diameter and 2.4 mm
in height. It is contemplated that other thermopile sensors may be
used, having different dimensions. Advantageously, the compact
dimensions of such a thermopile sensor enable the thermopile sensor
to be packaged within known meter configurations and positioned at
the test-sensor opening into which the test sensor is inserted.
[0058] In one study, a meter was configured with a Heimann HMS B21
Thermopile Sensor (Heimann Sensor GmbH). The HMS B21 Thermopile
Sensor operates similar to the HMS Z11-F5.5 Ultrasmall Thermopile
Sensor, described previously, but has larger dimensions, i.e., 8.2
mm in diameter and 3 mm in height. The study showed that although
the meter body had a temperature of approximately 30.degree. C.,
the thermopile sensor was able to measure the temperature of an
inserted test strip at room temperature, i.e. approximately
20.degree. C. It is contemplated that other thermopile sensors may
be used
[0059] In some embodiments, the temperature-measuring device 250
may also be employed to measure temperature change that indicates
the actual concentration of an analyte. For instance, reaction
between the analyte and the reagent may generate measurable heat
that indicates the concentration of the analyte in the sample.
[0060] In an alternative embodiment, the temperature-measuring
system 250 may include an optical-sensing system 250B as shown in
FIG. 5. Rather than measuring infrared radiation to calculate the
temperature of the test sensor 100, the meter 200 may measure
changes to temperature-sensitive or thermochromic materials that
are applied to the test sensor 100. Thermochromic materials change
color according to changes in temperature.
[0061] In general, thermochromism is the reversible change in the
spectral properties of a substance that accompanies heating and
cooling. Although the actual meaning of the word specifies a
visible color change, thermochromism may also include some cases
for which the spectral transition is either better observed outside
of the visible region or not observed in the visible at all.
Thermochromism may occur in solid or liquid phase.
[0062] Light can interact with materials in the form of reflection,
adsorption or scattering, and temperature-dependent modifications
of each of these light-material interactions can lead to
thermochromism. These thermochromic materials may include leuco
dyes and cholesteric liquid crystals. Other thermocromic materials
also include electroactive polymers, such as polyacetylenes,
polythiophenes, or polyanilines. Classes of thermochromic materials
are illustrated according to the physical background in TABLE
1.
TABLE-US-00001 TABLE 1 Thermochromic Material Material feature
Interaction Cholesteric liquid crystals Periodic structure
Reflection Crystalline colloidal arrays embedded in a gel network
Inorganic salts Conjugated polymers Chromophoric group Absorption
Hydrogel-indicator dye systems Leuco dye-developer-solvent systems
Hydrogel exhibiting LCST Areas with different Scattering Polymer
blends exhibiting refractive indices LCST
[0063] Such temperature-sensitive materials may generally be
applied on any portion of the meter-contact area 112. In the
embodiment of FIG. 1, a thermochromic material may be applied to
the auto-calibration information area 120. Referring back to FIG.
5, a general configuration for the optical-sensing system 250B is
illustrated. The optical-sensing system 250B may include a light
source 252B and a detector 254B. The light source 252B transmits
photons from the thermchromic material, and the detector 254B
receives the photons that are reflected from the thennchromic
material. For example, the light source 252B may be one or more
laser LEDs, while the detector 254B may be one or more photodiodes.
For materials, such as ChromaZone (a microencapsulated
thermochromic pigment) which changes from color to colorless as the
temperature increases, and vice versa, the temperature can be
determined by measuring the level of reflection from the
material.
[0064] Although the optical-sensing system 250B may actually
measure the temperature of the test sensor 100, i.e. the
meter-contact area 112, instead of the temperature of the reagent
115, the temperatures of the test sensor 100 and the reagent 115
are generally at equilibrium with the ambient temperature when the
test sensor 100 when the test sensor 100 is inserted into the
test-sensor opening 210 at time t.sub.1. As described previously,
when the test sensor 100 is inserted into the test-sensor opening
210, the meter-contact area 112 is positioned in the test-sensor
opening 210, but the fluid-receiving area 110 may be positioned
distally from the meter 200. As such, the meter-contact area 112
may be heated by sources of heat in the meter 200, such as
components receiving power from a power source. However, the
fluid-receiving area 110 and the reagent 115 may be sufficiently
spaced from the sources of heat to remain substantially at ambient
temperature. Thus, determining the ambient temperature provides a
useful estimate of the temperature of the reagent 115, which is
used as a factor in determining analyte concentration. It has been
determined that for a short period time, e.g., approximately 0.5
seconds to approximately 5 seconds, after the test sensor 100 has
been inserted into the test-sensor opening 210 at time t.sub.1, the
ambient temperature can still be determined from the meter-contact
area 112 before the temperature of the area 112 increases due to
the heat from the meter 200 or decreases due to the cooling from
the meter 200. Accordingly, some embodiments of the present
invention measure the temperature of area 112 at time t.sub.1 when
the effects of heat or cooling from the meter 200 are still at a
minimum. As described previously, other embodiments may measure the
temperature at other times and account for the effects of heating
or cooling from the meter 200 by applying an algorithm.
Furthermore, as also described previously, alternative embodiments
may include more than one structure disposed anywhere relative to
the meter body 205 for measuring more than one area of the test
sensor 100 inside or the outside test-sensor opening 210.
[0065] To further explain aspects of embodiments employing a
thermochromic material, thermochromic liquid crystals (TCLCs) are
described in detail. Thin film TCLCs are commercially available.
For example, FIG. 6 illustrates a test sensor 100 that is
configured to use a TCLC 130B. The TCLC 130B is applied in an area
133B that is defined by a thin cured material 132B, such as an
epoxy resin, which is applied to a back layer or window 135B. A
front window or substrate 134B is formed over the TCLC 130B.
[0066] In some embodiments, an array of thermochromic materials
corresponding to varying temperature ranges may be employed to
measure the temperatures. For example, FIG. 12 illustrates "a
sliced-pie TCLC configuration" 300 including eight TCLC circular
segments 310, each being sensitive for a smaller temperature range.
Eight miniature LEDs 320 are sequentially employed, and a single
miniaturized RGB 330 is placed in the center to detects the
corresponding color.
[0067] TCLCs may provide certain advantages over other
thermochromic materials. For example, while leuco dyes may provide
a wide range of colors, TCLCs may respond more precisely and can be
engineered for more accuracy than leuco dyes. It is understood,
however, that the examples provided herein are provided for
illustrative purposes only.
[0068] TCLCs are characterized by well analyzed reflections of the
visible light within a certain bandwidth of temperature. Typically,
TCLC's are specified for their color play. The resulting color play
is highly sensitive to changes in temperature. A certain
temperature leads to a certain reflected wavelength spectrum, with
a local maximum at a certain wavelength and a narrow bandwidth.
Accordingly, the optical-sensing system 250B may employ a liquid
crystal temperature sensor that can be optimized to read a
temperature range of approximately 5.degree. C. to 40.degree. C.,
for example. In this example, the lower end of the range of
5.degree. C. may be referred to as the "Red Start" temperature, and
the higher end of 40.degree. C. may be referred to as the "Blue
Start" temperature. The bandwidth between the Red Start and Blue
Start temperatures is thus 35.degree. C. It is contemplated that
Red and Blue Starts may vary from these examples.
[0069] When the temperature of the TCLC is below the Red Start
temperature, TCLC, particularly when applied in thin layers, are
optically inactive or transparent. Below the start temperature of
the color change, TCLCs hydrodynamically behave like a high
viscosity paste. They are transparent when applied in thin layers,
or milky-white in bulk. In this initial state, the molecules are
still ordered and close to each other as in a solid crystal, as
shown in FIG. 7. As the temperature increases toward the Red Start
temperature, the molecules are separated into layers as they pass
through the Smectic phase, but in this Mesomorphic state, the
crystals are still optically inactive or transparent.
[0070] Above the Red Start temperature, the molecules are in the
cholesteric state, where they are optically active and reflect the
light selectively and strongly depending on temperature. With
increasing temperature, the light reflected from the thermochromic
layer changes, in sequence, from red to orange, to yellow, to
green, and then to blue. The molecules are now arranged in layers,
within which the alignment is identical. In between layers,
however, the molecule orientation is twisted by a certain angle.
The light passing the liquid crystal (LC) undergoes Bragg
diffraction on these layers, and the wavelength with the greatest
constructive interference is reflected back, which is perceived as
a spectral color. As the crystal undergoes changes in temperature,
thermal expansion occurs, resulting in change of spacing between
the layers, and therefore in the reflected wavelength.
Specifically, cumulatively an overall helix-shaped architecture is
formed, and the molecular director traces out a helix in space. The
degree of twist is defined by the pitch length L.sub.0, which is
the height of the helical structure after one 360.degree. rotation.
The angle between two layers and thereby the pitch length of the
helix is proportional to the wavelength .lamda..sub.0 of the
selectively reflected light. This relationship can be described by
the Bragg diffraction equation, where n.sub.mean is the mean
refraction index and .phi. is the angle of the incident light beam
with respect to the normal of the surface:
.lamda..sub.0=L.sub.0n.sub.meansin .phi. (1)
[0071] If the temperature increases beyond the Blue Start
temperature, the molecular structure of the helix disbands and the
molecules are uniformly distributed like in an isotropic liquid. In
this state, the crystals are optically inactive again. Exceeding
the Blue Start temperature may lead to a permanent damage of the
TCLCs, depending on time and extent of the overheating.
[0072] The bandwidth of the TCLCs is defined as optical active
range and is limited downward by a Red-start temperature and upward
by a Blue-end temperature. The light passing the liquid crystal
undergoes Bragg diffraction on these layers, and the wavelength
with the greatest constructive interference is reflected back,
which is perceived as a spectral color. As the crystal undergoes
changes in temperature, thermal expansion occurs, resulting in
change of spacing between the layers, and therefore in the
reflected wavelength. The color of the thermochromic liquid crystal
can therefore continuously range from black through the spectral
colors to black again, depending on the temperature. as shown in
FIG. 8.
[0073] As the TCLCs only have thermochromic properties when they
are in the Cholesteric state, a thermochromic material having a
specified temperature range can be engineered by mixing different
cholesteric compounds.
[0074] To demonstrate the principle of some aspects of employing
TCLCs, an experiment was conducted. The first step included
preparing some cholesteryl ester liquid crystals using a known
method, based on G. H. Brown and J. J. Wolken, Liquid Crystals and
Biological Systems, Academic Press, N Y, 1979, pp. 165-167 and W.
Elser and R. D. Ennulat, Adv. Liq. Cryst. 2, 73 (1976), the
contents of which are incorporated herein by reference. The start
materials were: (A) Cholesteryl oleyl carbonate, (Aldrich
15,115-7), (B) Cholesteryl pelargonate (Cholesteryl nonanoate)
(Aldrich C7,880-1), and (C) Cholesteryl benzoate (Aldrich
C7,580-2). Different compositions of the mixture of these three
chemicals A, B, and C producing a liquid crystal film change color
over different temperature ranges as shown in TABLE 2.
TABLE-US-00002 TABLE 2 A = Cholesteryl B = Cholesteryl C =
Cholesteryl Transition oleyl Carbonate, g pelargonate, g benzoate,
g range, .degree. C. 0.65 0.25 0.10 17-23 0.70 0.10 0.20 20-25 0.45
0.45 0.10 26.5-30.5 0.43 0.47 0.10 29-32 0.44 0.46 0.10 30-33 0.42
0.48 0.10 31-34 0.40 0.50 0.10 32-35 0.38 0.52 0.10 33-36 0.36 0.54
0.10 34-37 0.34 0.56 0.10 35-38 0.32 0.58 0.10 36-39 0.30 0.60 0.10
37-40
[0075] These liquid crystals reversibly change color as the
temperature changes. An advantage of liquid crystals is their
ability to map out thermal regions of different temperature. The
liquid crystal mixture changes color with temperature. The TCLC
film may degrade when exposed to moisture or air, but as long as
they are stored in a sealed container the mixture may be prepared
months in advance.
[0076] The example experimental setup in the demonstration included
the TCLC films from Liquid Crystal Resources Inc (Glenview, Ill.),
an optical Red-Green-Blue (RGB) sensor and software TCS230EVM from
Texas Advanced Optoelectronic Solutions (Plano, Tex.), a
programmable heating and cooling plate IC35 from Torrey Pines
Scientific, Inc. (San Marcos, Calif.). Several K type thermocouples
from Omega Engineering Inc, Stamford Conn. were used to ascertain
the temperature on the heating-cooling plate. The TLC film was
attached to the heater/cooler plate, and temperature was set at
5-45.degree. C., in 5.degree. C. steps. Three thermocouples were
taped to the film and one to the plate. Two different TLC films
were used: 5-20.degree. C. and 20-40.degree. C. Both temperature
and RGB data were captured at a frequency of 20 Hz using DAQ.
[0077] The results of the example experimental setup above are
described. The temperature vs. time and optical intensity vs. time
data illustrated in FIG. 9 were converted to temperature vs. color
intensity data illustrated in FIG. 10.
[0078] FIG. 11A illustrates a subroutine for optical processing to
convert RGB data into temperature data. The optical data acquired
is in a three-column format with r.sub.s, g.sub.s, b.sub.s being
the values for red, green and blue sample. The data is used to
evaluate the ratios rg and rb. The ratios are then matched to the
mapping file which has the calibration data red, green, blue and
temperature data r.sub.c, g.sub.c, b.sub.c and T. FIG. 11B
illustrates a general algorithm to process optical data to convert
RGB data into temperature data.
[0079] Data for the 20.degree. C. to 40.degree. C. temperature
tests are shown in FIG. 12. As shown in FIG. 13, the
temperature-time and color intensity-time data are converted to
temperature-color intensity data. The TCLC-based temperature are
compared with thermocouple data in FIG. 15.
[0080] After applying the algorithms of FIGS. 11A and 11B, the
temperatures calculated from the RGB sensor follow the thermocouple
data closely. Accordingly, the demonstration above shows that
optical data can be converted into temperature data and the use of
optical data from TCLC film for temperature measurement is
feasible. In general, a TCLC film may be used in conjunction with
an RGB sensor for measuring the sensor temperature. The change in
color of the film may be calibrated to a temperature of the strip.
Furthermore, studies have shown that the technique of using a TCLC
film works for varying temperature differences between the sensor
and the meter. In one aspect, the temperature difference may be
approximately 45.degree. C. In another aspect, the temperature
difference may be approximately 25.degree. C. In yet another
aspect, the temperature difference may be approximately 10.degree.
C.
[0081] To measure the color of the TCLC, in one embodiment, the
optical-sensing system 250B may employ the general configuration
shown in FIG. 5. In particular, the light source 252B may be three
LEDs corresponding to red, green, and blue wavelengths, or may be a
single LED emitting white light. Three separate photodiodes with
filters measure the reflection R.sub.r, R.sub.g, and R.sub.h from
the TCLC corresponding to red, green, and blue wavelengths,
respectively. The ratio R.sub.r:R.sub.g:R.sub.b changes according
to color change in the TCLC. As the TCLC changes from red to green
to blue with increasing temperatures, the ratios R.sub.r:R.sub.b
and R.sub.r:R.sub.g decrease with the increase in temperature.
Thus, the temperature of the TCLC may be determined from the ratio
R.sub.r:R.sub.g:R.sub.b. Other ratios between R.sub.r, R.sub.g, and
R.sub.b may be employed by other embodiments. In addition, a
calibration feature may be required for this embodiment.
[0082] In yet another embodiment, the optical-sensing system 250B
may also employ the general configuration shown in FIG. 5. However,
the light source 252B may be a LED emitting a white light, while
the detector 254B may be an integrated red/green/blue (RGB) color
sensor detecting the level of red, green, and blue light reflecting
from the TCLC. The amounts of red, green, and blue light indicate
the color and thus the temperature of the TCLC.
[0083] In a further embodiment, the optical-sensing system 250B
also employs the general configuration shown in FIG. 5. In this
embodiment, the light source 252B may be a LED emitting photons of
a certain wavelength, while the detector 254B may be a photodiode
measuring the reflection of photons of the certain wavelength. The
amount of reflection changes as the color of the TCLC changes.
Thus, the measured reflection indicates the temperature of the
TCLC.
[0084] Rather than using the general configuration of FIG. 5, the
optical-sensing system 250B in an alternative embodiment may employ
an assembly that integrates illumination optics and receiver
circuitry, including a red/green/blue (RGB) color sensor. This
"hybrid" assembly, or combined structure, employs separate LED
light sources to transmit red, green, and blue light to the TCLC.
The reflected signal for each color may then be measured and
converted into 16-bit data, for example, to enable color
recognition, and thus a temperature reading, by the processing
system 230.
[0085] Referring to FIG. 16, another embodiment for a
temperature-measuring system 250 is illustrated. In particular, the
embodiment of FIG. 16 employs an optical-sensing system 250C that
includes a light source 252C and a detector array 254C. The light
source 252C may be a laser that emits a high coherence of a fixed
wavelength .lamda.. (Alternatively, the light source 252C may
include a light-emitting diode (LED) and filters to generate light,
e.g., a narrow band light beam, of fixed wavelength .lamda..) The
wavelength .lamda., for example, may be in the visible range, e.g.,
approximately 700 nm. However, the wavelength .lamda. may generally
be in the range of approximately 450 nm to approximately 1800 nm.
Meanwhile, the detector array 254C may include a linear photodiode
array, e.g., silicon- or germanium-based photodiode array, that is
capable of receiving and detecting light at any location along the
length of the array. The detector array 254C generates a voltage or
current signal that communicates the location. where light has been
detected.
[0086] In contrast to the optical-sensing system 250B of FIG. 5,
which measures changes to thermochromic materials applied to the
test sensor 100, the optical-sensing system 250C measures changes
to the structure of a grating 130C disposed along the surface of
the test sensor 100. As described in further detail below, the
structure of the grating 130C provides an indicator for
temperature. In particular, the grating 130C includes a series of
parallel linear structures 131C, which are spaced equally at a
fixed distance d. For example, the distance d may be approximately
600 nm. However, the distance d may vary in relation to the
wavelength .lamda.. On some typical test sensors, the grating 130C
may be sized approximately 1 mm.times.1 mm. In some embodiments,
the grating 130C may be formed directly on the test sensor 100,
which may be made from a polymer, such as PET (polyethylene
terephalate). For example, a series of equidistant parallel grooves
may be rolled into the material of the test sensor 100. In another
example, laser processing may be employed to engrave a series of
equidistant parallel grooves into the surface of the test sensor
100. In other embodiments, the grating 130C may be formed from
another material and placed or affixed onto the surface of the test
sensor 100. For example, a material may be applied to the surface
of the test sensor 100 by deposition to provide a grating
structure. In general, the grating 130C has substantially the same
temperature of the underlying test sensor 100.
[0087] As shown in FIG. 16, the light source 252C directs light of
fixed wavelength toward the grating 130C at a given angle of
incidence. The grating 130C causes diffraction of the light, and
the diffracted light is received by the detector array 254C.
According to the diffraction equation:
m.lamda.=d sin .theta. (2),
where d is the distance between the linear structures 131C for the
grating 130C, .lamda. is the wavelength of the incident light from
light source 252C, .theta. is the angle at which the light is
directed from the grating 130C, and m is an integer representing
each maxima for the diffracted light. For a given maxima in the
diffraction pattern, light of wavelength .lamda. reflects at a
specific angle .theta. off the grating 130C. The optical-sensing
system 250C may be configured so that the detector 254C detects
light corresponding to a given maxima, e.g., first order maxima at
m=1. The angle .theta. from the grating 130C can be determined
according to the location where the detector array 254C receives
the light from the grating 130C. Thus, for a given wavelength
.lamda. , the angle .theta. measured with the detector 254C
indicates the distance d between the structures 131C.
[0088] The grating 130C is formed from a material that is sensitive
to temperature. In general, the material expands when the
temperature T increases, and the material contracts when the
temperature T decreases. Correspondingly, the distance d between
the linear structures 131C changes according to the temperature of
the material. In other words, the distance d increases when the
temperature T increases and decreases when the temperature T
decreases. The distance d is a function of temperature, d(T), and
from equation (2) above:
sin .theta.=m .lamda./d(T) (3).
[0089] Thus, the angle .theta. is also a function of temperature
and can be measured with the detector 254C to determine the
temperature T of the grating material. Because the grating 130C is
thermally coupled to the test sensor 100, the temperature T of the
grating material also indicates the temperature of the underlying
test sensor 100. Preferably, the grating 130C is formed from a
material with a sufficiently high coefficient of thermal expansion,
so that the grating 130B has a highly detectable sensitivity to
temperature and the temperature measurement can be achieved with
greater accuracy. In addition, a more accurate determination of the
angle .theta. may be achieved by positioning the detector array
254C at a greater distance from the grating 130C, although the
positioning of the detector array 254C may depend on how the
optical-sensing system 250C is assembled in the meter 200. The
correlation between the measured angle .theta. and the temperature
T can be determined empirically for a given material and
configuration of the grating 130C. As a result, the optical-sensing
system 250C illustrated in FIG. 16 may be employed to estimate the
temperature of the reagent and, as described previously, to obtain
a more accurate calculation of the concentration of analyte in a
sample collected on the test sensor 100.
[0090] Referring to FIG. 17, another embodiment for a
temperature-measuring system 250 is illustrated. The embodiment of
FIG. 17 employs an optical-sensing system 250D that includes a
light source 252D and a detector 254D. However, instead of
providing a laser of a fixed wavelength .lamda. , the light source
252D emits white light. In one embodiment, the light source 252D
may be an LED. Meanwhile, the detector 254D may include an
integrated red/green/blue (RGB) color sensor. For example, the
detector 254D may include RGB photodiodes that provide a voltage or
current signal that indicates the level of red, green, and blue
components in the light received by the detector 254D.
[0091] A grating 130D similar to the grating 130D of FIG. 16 is
disposed along the surface of the test sensor 100. The grating 130D
includes a series of parallel linear structures 131D, which are
equally spaced at a fixed distance d. As described previously, the
material forming the grating 130D expands and contracts in response
to the temperature. Correspondingly, the distance d increases and
decreases when the material responds to the temperature.
[0092] As shown in FIG. 17, the light source 252D directs white
light toward the grating 130D. The grating 130D causes diffraction
of the white light, and some of the diffracted light is received by
the detector 254D. According to the wavelength dependence shown in
the grating equation (2) above, the grating 130D separates the
incident white light into its constituent wavelength components,
and each wavelength component is emitted from the grating 130D at a
particular angle .theta.. The detector 254D is not configured as an
array that receives all wavelength components from the grating
130D. Thus, as shown in FIG. 17, the detector 254D receives the
diffracted light within a range of angles .theta.. The detector
254D detects the red, green, and blue components of the light it
receives. A RGB numerical value can be generated to represent the
level of red, green, and blue components in the light received by
the detector 254D.
[0093] However, as described previously, the distance d between the
linear structures 131D changes when the temperature changes. The
change in distance d also changes the diffraction of light from the
grating 130D. In particular, the angle .theta. changes for each
wavelength component in the incident white light. Moreover, the
light received by the detector 254D within the range of angles
.theta. changes. With the change in the received light, the red,
green, and blue components measured by the detector 254D also
changes. In other words, the light received by the detector 254D
experiences a color shift when the temperature changes. For
example, a color shift that increases the level of blue in the
received light may indicate a decrease in temperature, while a
color shift that increases the level of red in the received light
may indicate an increase in temperature. Correspondingly, the RGB
numerical value representing the level of red, green, and blue
components in the received light also changes.
[0094] Accordingly, the color, i.e. the RGB numerical value, of the
light received by the detector 254D can be measured to determine
the temperature T of the grating material. Because the grating 130D
is thermally coupled to the test sensor 100, the temperature T of
the grating material also indicates the temperature of the
underlying test sensor 100. Preferably, the grating 130D is formed
from a material with a sufficiently high coefficient of thermal
expansion, so that the grating 130D has a highly detectable
sensitivity to temperature and the temperature measurement is
accurate. The correlation between the color and the temperature T
can be determined empirically for a given material and
configuration of the grating 130C. As a result, the optical-sensing
system 250D illustrated in FIG. 17 may be employed to estimate the
temperature of the reagent and, as described previously, to obtain
a more accurate calculation of the concentration of analyte in the
sample collected on the test sensor 100.
[0095] Referring to FIG. 18, yet another embodiment for a
temperature-measuring system 250 is illustrated. The embodiment of
FIG. 18 employs an optical-sensing system 250E that includes a
light source 252E and a detector 254E. The light source 252E may be
a laser that emits a high coherence of a fixed wavelength .lamda. .
(Alternatively, the light source 252C may include a light-emitting
diode (LED) and filters to generate light, e.g., a narrow band
light beam, of fixed wavelength .lamda. .) Meanwhile, the detector
254E may include a single photodiode that provides a current or
voltage signal indicating the amount of light received by the
photodiode. Rather than a grating, however, a polarizing material
130E is disposed along the surface of the test sensor 100.
[0096] As shown in FIG. 18, the light source 252D directs the laser
toward the polarizing material 130E and light is reflected from the
polarizing material 130E to the detector 254E. The polarizing
material 130E causes a change in the polarization of the light from
the light source 252E. As shown further in FIG. 18, a polarizing
filter 255E is disposed between the polarizing material 130E and
the detector 254E, so that only light that is polarized in a
particular direction passes to the detector 254E. Thus, the amount
of light received by the detector 254E depends on the polarization
of the reflected light. However, the structure of the polarizing
material 130E and thus the degree of polarization of the reflected
light depends on the temperature. Any change in the degree of
polarization of the reflected light results in a change in the
amount of light received by the detector 254E. Thus, the amount of
light the detector 254D receives can be measured to determine the
temperature T of the polarizing material 130E. Because the
polarizing material 130E is thermally coupled to the test sensor
100, the temperature T of the polarizing material 130E also
indicates the temperature of the underlying test sensor 100. The
correlation between the amount of light received by the detector
254E and the temperature T can be determined empirically for a
given polarizing material 130E. As a result, the optical-sensing
system 250E illustrated in FIG. 18 may be employed to estimate the
temperature of the reagent and, as described previously, to obtain
a more accurate calculation of the concentration of analyte in the
sample collected on the test sensor 100.
[0097] Although the embodiments described herein provide more
accurate temperature readings than conventional systems, it has
been discovered that further accuracy may be achieved by optimal
positioning of the sensor of the temperature-measuring system 250
within the test-sensor opening 210. For example, as shown in FIG.
3E, the thermopile sensor 250A occupies a position 251 within the
test-sensor opening 210. In some embodiments, this may mean that
the sensor 250A is positioned near the electrical contacts that
receive the test sensor electrodes. When the thermopile sensor 250A
is positioned more deeply within the interior of the meter 210 in
the direction X shown FIG. 3E, the thermopile sensor 250A measures
the temperature at a region 113 of the meter-contact area 112 where
heat transfer from the meter 200 is minimized. In one aspect,
convective heat transfer is reduced at positions deeper within the
test-sensor opening 210. Thus, the temperature at a region deeper
within the test-sensor opening 210 changes more slowly, so that
there is a greater chance of obtaining an accurate measurement of
the temperature of the test sensor 100 without the effects of heat
transfer from the meter 200.
[0098] In the embodiments described herein, heat transfer to the
measured region 113 on the test sensor 100 may also be minimized by
providing a space between the region 113 and the thermopile sensor
250A to create an insulating air pocket around the region 113. In
addition, conductive heat transfer to the test sensor 100 may be
reduced by employing point contacts, rather than surface contacts,
where any contact between the meter 200 and the test sensor 100 is
necessary.
[0099] In general, the meter 200 employs an architecture that
combines an analog front end with a digital engine. Typically, the
analog front end relates to components such as the measurement
system 220. Meanwhile, the digital engine executes data processing
functions and controls electronic components such as the user
interface 240. It is contemplated that the architecture in the
embodiments described herein can be configured so that the
temperature-measuring system 250 may be integrated with the analog
front end or the digital engine. Advantageously, when the
temperature-measuring system 250 is integrated with the analog
front end, fewer electronic components are required for designing
and implementing the temperature-measuring system 250. On the other
hand, when temperature-measuring system 250 is integrated with the
digital engine, the architecture enables different configurations
for an analog front end to be designed and implemented with the
digital engine without having to design each front end
configuration to handle temperature measurement functions.
[0100] Although the embodiments described herein may measure the
temperature of one or more areas of a test sensor to determine the
temperature of a reagent disposed on the test sensor, it is
contemplated that the temperature of the reagent may be measured
directly according to the techniques described. For example, a
thermochromic material may be applied at or near the reagent to
measure the temperature of the reagent.
[0101] The temperature measurement techniques described herein may
also be used in a controller employed in combination with a
continuous glucose monitoring (CGM) system 400 as shown in FIG. 19.
Typically in the CGM system 400, a CGM sensor 410 is attached to a
user. The CGM sensor 410 may be placed in contact or optical
communication with the user's blood or interstitial fluid to
measure a desired analyte concentration in the sample. The CGM
sensor 410 may measure a desired analyte concentration of the user
through the skin. Once the CGM sensor 410 has measured a analyte
concentration, i.e., glucose, as known to those in the art, a
signal is sent to a controller 420 or similar device. The CGM
system 400 may take measurements at different time intervals. As
illustrated, the controller 420 is remote from the CGM sensor 410
in FIG. 19, but in other embodiments, the controller 420 may be
attached to the CGM sensor 410. However, most CGM systems must be
calibrated at different time intervals such that the CGM system
produces a more accurate value. To calibrate the CGM system 400, a
discrete blood glucose meter, such as the embodiments described
above, may be used to provide an accurate reading at a given time
frame. The reading can then be used to calibrate CGM system 400.
The meter used for such a task may be a meter 200 or other meters
described previously herein or the meter may simply be a module 430
that is contained within controller 420. The controller 420
provides similar functions as meter 200 and has like components as
previous embodiments discussed herein. The module 430 may be
integral with controller 420 or simply be a component part that is
added into the controller. The module 430 has an opening 432 to
receive a test sensor strip, which may be similar to sensor 100 or
other embodiments as previously described herein and can calculate
the concentration of glucose in a sample as earlier described with
reference to previous embodiments. In an alternate embodiment, some
of the software or other electrical components required to
calculate the concentration of glucose in the sample may be
contained on the controller 420 apart from the module 430. In
either case the module 430 may have a connector 434 that
electrically or optically connects the module 430 to the controller
420. The controller may also have a display 440 so as to display
the measured glucose reading. The module 430, similar to previous
embodiments may include one or more temperature measuring systems
250. The temperature measuring system 250 may employ the
measurement techniques described herein or may include aspects of
the temperature measuring systems described herein. For example,
the temperature measuring system 250 may include a thermopile
sensor or employ an optical-sensing system to provide more accurate
measurements that account for temperature effects. The components
may be positioned or configured similarly as previously
discussed.
[0102] While various embodiments in accordance with the present
invention have been shown and described, it is understood that the
invention is not limited thereto. The present invention may be
changed, modified and further applied by those skilled in the art.
Therefore, this invention is not limited to the detail shown and
described previously, but also includes all such changes and
modifications.
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