U.S. patent application number 12/757695 was filed with the patent office on 2010-10-14 for method for estimating distribution of sample.
This patent application is currently assigned to BIONIME CORPORATION. Invention is credited to Cheng-Teng Hsu, Chun-Mu Huang.
Application Number | 20100258453 12/757695 |
Document ID | / |
Family ID | 42272495 |
Filed Date | 2010-10-14 |
United States Patent
Application |
20100258453 |
Kind Code |
A1 |
Huang; Chun-Mu ; et
al. |
October 14, 2010 |
METHOD FOR ESTIMATING DISTRIBUTION OF SAMPLE
Abstract
The present invention relates to a method for estimating a
distribution of a sample flowed from a first electrode toward a
second electrode of an electrochemical test strip. A working
voltage is provided between the first electrode and the second
electrode for obtaining a first and a second currents, where a
ratio of the first current to the second current is applied to
estimate the distribution of the sample on the first and the second
electrodes and an effectiveness of a measurement of a target
analyte of the sample.
Inventors: |
Huang; Chun-Mu; (Sanchung
City, TW) ; Hsu; Cheng-Teng; (Dali City, TW) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.
UNITED PLAZA, 30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
BIONIME CORPORATION
Dali City
TW
|
Family ID: |
42272495 |
Appl. No.: |
12/757695 |
Filed: |
April 9, 2010 |
Current U.S.
Class: |
205/777.5 ;
205/775 |
Current CPC
Class: |
G01N 27/404 20130101;
G01N 27/3273 20130101; G01N 27/3271 20130101; G01N 27/3272
20130101 |
Class at
Publication: |
205/777.5 ;
205/775 |
International
Class: |
G01N 27/26 20060101
G01N027/26 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2009 |
TW |
098111902 |
Claims
1. A determining method for a sensor having at least a first
electrode and a second electrode, comprising the steps of: (a)
providing a target sample flowing from the first electrode to the
second electrode; (b) applying a first DC voltage with a voltage
value across the first electrode and the second electrode for a
first duration to make a potential of the first electrode higher
than a potential of the second electrode and to generate a first
Cottrell current; (c) removing the first DC voltage; (d) applying a
second DC voltage with a voltage value across the first electrode
and the second electrode for a second duration to make the
potential of the second electrode higher than the potential of the
first electrode and to generate a second Cottrell current, wherein
the respective voltage values of the first and the second DC
voltages are equal; (e) removing the second DC voltage; (f)
repeating steps (b) to (e) at least twice; (g) adding up respective
values of the first Cottrell currents and respective values of the
second Cottrell currents respectively; and (h) obtaining a ratio of
a sum of the respective values of the first Cottrell currents over
a sum of the respective values of the second Cottrell currents to
determine a distribution of the target sample on the first and the
second electrodes.
2. A method according to claim 1, wherein the first and the second
DC voltages are determined via a cyclic voltammograms, and an S/N
ratios of the first DC voltage and the second DC voltage are not
smaller than 1.
3. A method according to claim 1, wherein the sensor has a
substrate on which the first and the second electrodes are
configured.
4. A method according to claim 1, wherein the first and the second
electrodes have an enzyme and an electron transfer mediator
thereon, and the enzyme makes the target sample generate a reaction
being one selected from a group consisting of an oxidation, a
reduction and a redox.
5. A method according to claim 1, wherein the first and the second
durations are between 3 ms to 2 s.
6. A method according to claim 1, wherein the first and the second
durations are equal.
7. A method according to claim 1, wherein the first and the second
DC voltages are removed for a first removing and a second removing
durations respectively, and the first removing and the second
removing durations are between 0 ms to 50 ms.
8. A method according to claim 1, wherein the first and the second
DC voltages are removed for a first removing and a second removing
durations respectively, and the first removing and the second
removing durations are equal.
9. A method according to claim 1, wherein the first electrode and
the second electrodes have respective electrochemical reaction
areas being equal to each other.
10. A method according to claim 9, wherein both the first and the
second electrodes are fully covered thereon by the target sample
when the ratio is 1.
11. A method according to claim 1, wherein the first electrode and
the second electrodes have respective electrochemical reaction
areas, and the electrochemical reaction area of the first electrode
is not equal to that of the second electrode.
12. A method according to claim 1, wherein the sensor is an
electrochemical sensor.
13. A method according to claim 1 being used for determining an
effectiveness of a detection to the target sample.
14. A method according to claim 13, wherein the detection is
effective when the ratio is between 0.3 and 3.0.
15. A method according to claim 1, wherein the value of the first
Cottrell current and the value of the second Cottrell current are
recorded during the first and the second durations
respectively.
16. A determining method for a distribution of a target sample,
comprising the steps of: (a) providing a first and a second
electrodes; (b) providing the target sample flowing from the first
electrode to the second electrode; (c) applying a first DC voltage
having a voltage value across the first electrode and the second
electrode to make a potential of the first electrode higher than a
potential of the second electrode and to generate a first sensing
current; (d) removing the first DC voltage; (e) applying a second
DC voltage having the voltage value across the first electrode and
the second electrode to make the potential of the second electrode
higher than the potential of the first electrode and to generate a
second sensing current; and (f) obtaining a ratio of a value of the
first sensing current over a value of the second sensing current to
determine the distribution of the target sample on the first and
the second electrodes.
17. A method according to claim 16, wherein the first and the
second electrodes are configured on an electrochemical strip.
18. A method according to claim 16, wherein the first and the
second DC voltages are applied for a period for 3 ms to 2 s.
19. A method according to claim 16, wherein the first and the
second sensing currents are Cottrell currents.
20. A determining method, comprising the steps of: (a) providing a
first and a second electrodes; (b) providing a target sample
flowing from the first electrode to the second electrode; (c)
making a potential of the first electrode higher than a potential
of the second electrode and to generate a first sensing current;
(d) making the potential of the second electrode higher than the
potential of the first electrode and to generate a second sensing
current; and (e) obtaining a ratio of a value of the first sensing
current over a value of the second sensing current to determine the
distribution of the target sample on the first and the second
electrodes.
Description
TECHNICAL FIELD
[0001] The present invention is related to a method for estimating
the effectiveness of the test and/or the measurement performed by a
meter. In particular, the present method uses a ratio obtained from
a series of values of currents to reveal the distribution of a
target sample covered on the electrodes of an electrochemical test
apparatus, e.g. an electrochemical test strip, and estimate the
effectiveness of the test and/or the measurement performed by the
meter being inserted with the electrochemical test strip.
DESCRIPTION OF RELATED ART
[0002] Electrochemical sensing systems for analyzing analytes in a
biological samples are widely used. For example, analytes such as
glucose level, cholesterol level or uric in a sample such as blood
may be analyzed. Generally speaking, such electrochemical sensor
systems include a test strip and a measuring meter. In particular,
those test strips are provided as single use and disposable ones
for easy home use.
[0003] The electrochemical sensor using enzymatic amperometric
methods are well known. The sensors of such systems have electrodes
which are coated with a reagent including enzymes. The electrodes
are used to sense an electrochemical current which is produced by a
reaction between the reagent and the analyte(s) in a test
sample.
[0004] The enzyme is used for a unity, well specified reaction with
a specific analyte in the test sample. This specific reaction
reduces the interference with other analytes. For example, a
reagent with a specific cholesterol enzyme may be used to test
cholesterol level in a sample. A reagent with a glucose oxidase may
be used to measure the glucose level in a blood sample.
[0005] The glucose oxidase does not react with the cholesterol, nor
with other sugars in the blood sample. The use of glucose oxidase
e.g. typically leads to a 99% unique selection of glucose within
the sample. Methods based on the use of enzyme are leading to most
accurate measurement results.
[0006] In the method for determining the concentration of the
analyte in the sample by the sensing current, the sensing current
is measured and called the Cottrell current. The Cottrell current
is obtained by the following equation (Cottrell Equation).
i(t)=KnFACD.sup.0.5t.sup.-0.5
Where, i is an instant value of the sensing current; K is a
constant; n is the transferred number of electrons; F is the
Faraday constant; A is the surface area of the working electrode; C
is the concentration of the analyte in the sample; D is the
diffusion coefficient of the reagent; and t is a specific time
after a predetermined voltage has been applied to the
electrodes.
[0007] Generally speaking, as to the constructions of known
disposable electrochemical test strips and measurement procedures
thereof, the following elements/steps are included.
[0008] 1. A base sheet is used to be the substrate.
[0009] 2. At least two separate electrodes are configured in the
base sheet, where both the two separate electrodes have two
terminals, a first and a second terminals. The first and the second
terminals of the first one of the electrodes are used to be a
"working electrode" and an output terminal of the working electrode
respectively, wherein the output terminal of the working electrode
is electrically connected to a measuring meter. The first and the
second terminals of the second one of the conductive electrodes are
used to be a "counter electrode" and an output terminal of the
counter electrode respectively, wherein the output terminal of the
counter electrode is electrically connected to the measuring meter.
The working electrode and the counter electrode are near configured
on the base sheet to form an electrode measuring region.
[0010] 3. The electrode measuring region is coated with chemical
reagents including the enzyme and used to chemically react with a
specific analyte in fluid sample.
[0011] 4. A working voltage provided by the measuring meter is
applied between the working electrode and the counter electrode.
The working voltage and the polarity thereof are used to make the
chemical reaction is under the oxidative state (where the working
voltage applied on the working electrode is positive at this time)
or reductive state (where the working voltage applied on the
working electrode is negative at this time). During the oxidative
state or the reductive state, the electrochemical current of the
chemical reaction can be measured and such the electrochemical
current is the Cottrell current.
[0012] 5. The concentration of the specific analyte can be obtained
by the measured electrochemical current (Cottrell current) and the
above-mentioned Cottrell Equation (i(t)=KnFACD.sup.0.5
t.sup.-0.5).
[0013] The chemical reagent with the enzyme coated on the working
electrode is used to generate a chemical reaction with the specific
analyte in the fluid sample. Then, the working voltage is applied
on the surface of the working electrode when the chemical reaction
reacts and thus the electrochemical current generated on the
oxidative region (or the reductive region) can be measured and is
the called Cottrell current. The counter electrode is used to be
the relative current loop when measuring the electrochemical
current (the Cottrell current).
[0014] The value of the working voltage applied in the chemical
reaction can be chosen from the known cyclic voltammograms to
obtain the appropriate oxidative and/or reductive potentials, which
is elaborated as follows.
[0015] 1. Circularly changing the value of the working voltage
applied on the working electrode to measure the various values of
currents corresponding to the circularly changed the working
voltages. From such procedure, the cyclic voltammograms as shown in
FIG. 1(A) can be obtained and the Point I reveals the anodic
(oxidative) peak current. The voltage corresponding to the anodic
peak current (Point I) is the anodic (oxidative) working voltage
(V.sub.I) which is the most appropriate and sensitive one for the
chemical reaction. By applying the anodic working voltage (V.sub.I)
to the working electrode, the optimum signal to noise ratio (S/N
ratio) will be obtained. Point I also reveals the optimum working
potential of the oxidative reaction by which the optimum Cottrell
current II can be obtained and the S/N ratio will be higher than or
equal to 1. If V.sub.II (corresponding to Point II) is applied to
the working electrode, the most optimum Cottrell current having the
optimum S/N ratio cannot be obtained.
[0016] 2. The voltage corresponding to the current peak (Point III)
of the cyclic voltammograms is the most sensitive cathode
(reductive) working voltage (V.sub.III) for the chemical reaction.
Point III reveals the optimum reactive working potential by which
the optimum Cottrell current IIII can be obtained and the S/N ratio
will be higher than or equal to 1.
[0017] 3. Selecting the appropriate voltage polarity and the value
of the working voltage based on the above-mentioned cyclic
voltammograms and procedures to apply thereto the working electrode
to measure and obtain the Cottrell current generated by the
analytes and the chemical reagents during the oxidation (or the
reduction).
[0018] It is known from the Cottrell Equation that the
concentration of analytes C is proportional to the value of the
sensing current i, and therefore that the concentration of analytes
C can be obtained by the value i(t) of the sensing current. In
addition, because the surface area A of the working electrode is
also proportional to the value of the sensing current i, A is taken
as a constant for decreasing the variables in the Cottrell
Equation. However, the precise definition of the presumption of the
surface area A being the constant is "the surface area A is the
constant when the electrochemical currents are measured", and
therefore the condition, the surface of the working electrode is
necessary being totally covered when measuring the electrochemical
currents, should be considered for assuring the surface area A of
the working electrode is the constant. If the surface of the
working electrode is not totally covered by the fluid sample but
the surface area A is calculated within the Cottrell Equation, an
incorrect value of concentration of analytes C would be
obtained.
[0019] In brief, the concentration of the analytes in the sample
fluid can be obtained and is proportional to the value of the
sensing current i. Additionally, since the surface area A of the
working electrode is also proportional to the value of the sensing
current i, the precisely defined surface area of the working
electrode of the test strip is also a key factor for an accurate
meter measuring the concentration of analytes in the sample.
[0020] Furthermore, the determination as to whether the sample
volume distributed in the reaction region of the electrochemical
strip is enough is another important factor for the measurement of
the concentration of the alanyte in the sample fluid. If there is
enough sample fluid distributing in the reaction region of the
electrochemical strip, the concentration of the alanyte in the
sample fluid can be obtained according to the sensing current i and
the Cottrell Equation. On the contrary, if sample fluid is not
enough for distributing in the reaction region of the
electrochemical strip, the concentration of the alanyte in the
sample fluid obtained according to the sensing current i and the
Cottrell Equation is an incorrect one. Accordingly, under the
circumstance of the surface area of the wording electrode being
precisely defined, that whether the sample volume distributed in
the reaction region of the electrochemical strip is enough is one
of the important factors for the measurement of the concentration
of the alanyte in the sample fluid.
[0021] Such these sensors (test strips) and meters were disclosed
in U.S. Pat. No. 5,266,179, U.S. Pat. No. 5,366,609, or EP
1272833.
[0022] The operation principle of the measuring meters disclosed in
these patent documents is generally the same. First, a test strip
is inserted into the measuring meter. A proper insertion of the
test strip within the meter is detected by mechanical and/or
electrical switches or contacts. Once a test strip is properly
inserted into the measuring meter, the user is asked to provide a
sample, typically a drop of blood. The sample of blood is then fed
to a reaction zone on the test strip. The reaction zone of the test
strip is provided with at least two electrodes which are covered by
the reagent.
[0023] In order to detect presence of a sample in the reaction
zone, a voltage is applied to the electrodes. The resistance of the
reagent between the electrodes without the presence of a sample is
high. As soon as a sample is present in the reaction region, the
resistance between the electrodes (working electrode and counter
electrode) is reduced. Reduction of the resistance leads to flow of
a current which may be detected as an indication of the presence of
a sample.
[0024] For a more detailed explanation of the known
detecting/measuring methods as above-mentioned, please refer to
FIGS. 1(B) and 1(C).
[0025] FIG. 1(B) shows the measuring method for the conventional
meter, and is also the content of U.S. Pat. No. 5,366,609. FIG.
1(C) is the amplified diagram of scope S shown in FIG. 1(B) and
shows the currents generated by the voltage applied to the
electrodes on the test strip during the sample detecting
period.
[0026] As shown in FIG. 1(B), when the test strip is inserted into
the meter at time 100, a voltage 102 with a fixed value is applied
to the electrodes of the test strip during a sample detecting
period 101 for detecting whether a sample is present in the
reaction region. Next, a drop of the sample is added to the test
strip at time 108.
[0027] Please also refer to FIG. 1(C). When the current reaches a
sample detecting threshold 112, i.e. the sample is detected being
present in the reaction region, a sample volume delaying period 114
starts. In order to estimate whether the sample volume is enough,
the meter will continuously applies the voltage 102 to the
electrodes of the test strip until time 103.
[0028] Then, values of current 109 is compared with a sample volume
threshold 113 for determining the end of sample volume delaying
period 114. If the value (intensity) of the current is lower than
sample volume threshold 113, the meter will alarm to point out that
the volume of the sample in the test strip is not enough, and then
stops the measurement of the sample.
[0029] If there is sufficient sample volume in the reaction region,
e.g. revealing by time 115 where value of current 109 is higher
than sample volume threshold 113, the meter will start the
subsequent step of performing an incubation period 105. During
incubation period 105, the meter removes the fixed voltage 102 and
does not apply any voltage, i.e. apply a zero voltage 104, to the
electrodes of the test strip. In incubation period 105, a specific
and predetermined time is provided for the sample to be mixed and
dissolved with the reagents coated on the electrodes.
[0030] When incubation period 105 finishes, the meter starts a
measurement period 106 and apply a predetermined voltage 107 to the
electrodes of the test strip during measurement period 106. During
measurement period 106, the value of current 110 between the
electrodes will be measured.
[0031] The determination and the calculation of the concentration
of the analyte in the sample is based on the aforementioned
Cottrell current, and during measurement period 106 the value of
concentration of the analyte in the sample, calculated according to
the Cottrell Equation, will be shown on the display of the
meter.
[0032] Therefore, the definition and determination of sample
detecting threshold 112 are very important for estimating whether
the sample volume is enough.
[0033] Employing experiments and researches full-heartily and
persistently, the applicant finally conceived method for estimating
distribution of sample.
SUMMARY OF THE INVENTION
[0034] The present invention provides a method for estimating the
distribution of a sample fluid covering on the surfaces of the
electrodes of a electrochemical test apparatus, where the results
of the present method can be used for estimating the percentage of
the surface of the electrode covered by the sample fluid to
estimate the effectiveness and/or correctness of the measurement of
the concentration of the analyte in the sample. Moreover, the
results of the present method can be used for estimating the
above-mentioned effectiveness and/or correctness either prior to
the formally measurement of the concentration of the analyte or
after the measurement of the concentration of the analyte.
[0035] A reaction DC voltage is applied to the electrochemical test
apparatus having at least a first and a second electrodes during
sample detecting period 101, wherein the reaction DC voltage is
determined by the oxidative (or reductive) voltage which is
obtained from the cyclic voltammetry and able to make the optimum
oxidation (or reduction) of the electrochemical reaction occur.
[0036] On another aspect, the present disclosure provides a method
for a sensor having at least a first electrode and a second
electrode, comprising the steps of (a) providing a target sample
flowing from the first electrode to the second electrode; (b)
applying a first DC voltage with a voltage value across the first
electrode and the second electrode for a first duration to make a
potential of the first electrode higher than a potential of the
second electrode and to generate a first Cottrell current; (c)
removing the first DC voltage; (d) applying a second DC voltage
with a voltage value across the first electrode and the second
electrode for a second duration to make the potential of the second
electrode higher than the potential of the first electrode and to
generate a second Cottrell current, wherein the respective voltage
values of the first and the second DC voltages are equal; (e)
removing the second DC voltage; (f) repeating steps (b) to (e) at
least twice; (g) adding up respective values of the first Cottrell
currents and respective values of the second Cottrell currents
respectively; and (h) obtaining a ratio of a sum of the respective
values of the first Cottrell currents over a sum of the respective
values of the second Cottrell currents to determine a distribution
of the target sample on the first and the second electrodes.
[0037] On another aspect, the present disclosure provides a
determining method for a distribution of a target sample,
comprising the steps of providing a first and a second electrodes;
providing the target sample flowing from the first electrode to the
second electrode; applying a first DC voltage having a voltage
value across the first electrode and the second electrode to make a
potential of the first electrode higher than a potential of the
second electrode and to generate a first sensing current; removing
the first DC voltage; applying a second DC voltage having the
voltage value across the first electrode and the second electrode
to make the potential of the second electrode higher than the
potential of the first electrode and to generate a second sensing
current; and obtaining a ratio of a value of the first sensing
current over a value of the second sensing current to determine the
distribution of the target sample on the first and the second
electrodes.
[0038] On another aspect, the present disclosure provides a
determining method, comprising the steps of providing a first and a
second electrodes; providing a target sample flowing from the first
electrode to the second electrode; making a potential of the first
electrode higher than a potential of the second electrode and to
generate a first sensing current; making the potential of the
second electrode higher than the potential of the first electrode
and to generate a second sensing current; and obtaining a ratio of
a value of the first sensing current over a value of the second
sensing current to determine the distribution of the target sample
on the first and the second electrodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1(A) is a known cyclic voltammograms for an
electrochemical, FIG. 1(B) shows the measuring method of U.S. Pat.
No. 5,366,609, and FIG. 1(C) is the amplified diagram of scope S
shown in FIG. 1(B).
[0040] FIG. 2(A) is a schematic diagram of the appearance of meter,
FIG. 2(B) is a schematic diagram showing the front view (the left
one) and back view (the right one) of an electrochemical test
strip, and FIG. 2(C) shows the internal circuit configuration of
the conventional meter used for the electrochemical test strip.
[0041] FIGS. 3(A), 3(B), 3(C), 3(D) and 3(E) are the
cross-sectional diagrams of the electrochemical test strip and
illustrate the process of the sample flowing into the
electrochemical test strip.
[0042] FIGS. 4(A), 4(B) and 4(C) show the internal circuit of the
present meter suitable for the electrochemical test strip.
[0043] FIGS. 5(A), 5(B), 5(C), 5(D), 5(E), 5(F) and 5(G) are
partially amplified diagrams of the electrochemical test strip and
illustrate the process of the sample flowing into the
electrochemical test strip.
[0044] FIGS. 6(A), 6(B), 6(C) and 6(D) show the voltage and the
current generated during the electrochemical reaction occurring on
the electrochemical test strip, and 6(E), 6(F), 6(G) 6(H) and 6(I)
are the cyclic voltammograms during the electrochemical reaction
occurring on the electrochemical test strip.
[0045] FIGS. 7(A) and 7(B) show the internal circuit of another
embodiment of the present meter.
[0046] FIG. 8 shows the internal circuit of another embodiment of
the present meter.
[0047] FIG. 9(A) is another embodiment of the electrochemical test
strip, and FIG. 9(B) is a sectional drawing of the electrochemical
test strip shown in FIG. 9(A).
[0048] FIG. 10(A) is another embodiment of the electrochemical test
strip, FIG. 10(B) is an explosion drawing of the electrochemical
test strip shown in FIG. 10(A), and FIGS. 10(C) and 10(D) are the
sectional drawings of the electrochemical test strip shown in FIG.
10(A) and illustrate the process of the sample flowing into the
electrochemical test strip.
[0049] FIG. 11(A) is another embodiment of the electrochemical test
strip, FIG. 11(B) is an explosion drawing of the electrochemical
test strip shown in FIG. 11(A), and FIG. 11(C) is a sectional
drawings of the electrochemical test strip shown in FIG. 11(A).
DESCRIPTION OF THE EMBODIMENTS
[0050] The present invention provides a method for estimating the
distribution of a sample fluid covering on the surfaces of the
electrodes of a electrochemical test apparatus to estimate the
effectiveness and/or correctness of the measurement of the
concentration of the analyte in the sample, which can be fully
understood and accomplish by the skilled person according to the
following embodiments. However, the practice of the present method
is not limited into following embodiments.
[0051] Please refer to FIG. 2(A), which shows the appearance of
meter 10 applied for the electrochemical test strip. The meter 10
includes a shell with a display 12 showing measurement results, and
a slot 11 to be inserted by a sensor, e.g. an electrochemical test
strip 20. FIG. 2(B) shows the front view (the left one) and the
back view (the right one) of electrochemical test strip 20, wherein
electrochemical test strip 20 has electrodes 21 and 22.
[0052] FIG. 2(C) shows the internal circuit configuration of
conventional meter 10 used for the electrochemical test strip 20.
The meter 10 has a processor unit 13, a displayer 14, a power
supply unit 15, a current measurement unit 16, a current 17, a
current-to-voltage converter 18, an analog-to-digital convertor 19,
a current buffer 120, a voltage regulator 121, a temperature sensor
122, and a strip detecting unit 124 having a switch SW, wherein
current-to-voltage converter 18 is configured in current
measurement unit 16 and used for converting current 17 between
contacts 24 and 25 into an analog voltage Vo (where Vo=I.times.Rf).
The analog voltage Vo will be converted into an equivalent digital
signal for being calculated by processor unit 13.
[0053] The divider formed by voltage regulator 121 and resistors R1
and R2 applies the voltage to contact Vc1, and current buffer 120
has a capability for driving high current and outputs a potential
identical to that of contact Vc1 at contact Vc2. Under this
situation, the potential of contact 125 is Vw, the potential of
contact 126 is Vc, and an electrode voltage 123 is Vwc which is
equal to the potential difference between Vw and Vc. Electrode
voltage 123 is applied between contacts 125 and 126 respectively
electrically connected to outputting contacts 24 and 25 of
electrochemical test strip 20.
[0054] Please refer to FIGS. 3(A) to 3(E), wherein these figures
illustrate the process that the sample flows into electrochemical
test strip 20 and fully covers on electrodes 21 and 22.
[0055] FIGS. 3(A) to 3(E) are sectional drawings of electrochemical
test strip 20 taken along the line A-A', wherein electrochemical
test strip 20 has a channel 23, outputting contacts 24 and 25, a
sample entrance 26, a cover 27, an air hole 28, a sample 29, a
groove 210, upper surfaces of electrodes 211 and 212, through holes
213 and reagent 214, electrodes 21 and 22 are configured in through
holes 213 in groove 210 of electrochemical test strip 20, and the
respective areas of upper surfaces 211 and 212 are the same.
Electrodes 21 and 22 are tightly surrounded by through holes 213
without any gap. The diameters of through holes 213 are designed to
be slightly smaller than that of electrodes 21 or 22, so that
electrodes 21 and 22 can be mechanically engaged in through holes
213.
[0056] Respective upper surfaces 211 and 212 of electrodes 21 and
22 form the working area of electrode, and respective sizes of
upper surfaces 211 and 212 can be the same to or different from
each other. The bottoms of electrodes 21 and 22 are outputting
contacts 24 and 25 of electrochemical test strip 20, and outputting
contacts 24 and 25 respectively connected to contacts 125 and 126
of meter 10 as shown in FIG. 2(C). Cover 27 is a hydrophilic one
and has air hole 28 linked with the outside world. Cover 27 is
further configured to cover groove 23 to form channel 23, wherein
channel 23 is a capillary and defines a reaction region which is
coated with reagent 214, and reagent 214 is covered on upper
surfaces 211 and 212 of electrodes 21 and 22. Reagent 214 includes
a known oxidative or reductive enzyme such as a glucose oxidase, an
electron transport intermediate such as the potassium ferrocyanide
(Fe(CN)63-), as well as some hydrophilic chemicals. The
compositions of reagent 214 are the common means and not the focal
point of the present invention. In addition, electrochemical test
strip 20 provides sample entrance 26 for receiving sample 29, e.g.
a drop of blood.
[0057] Please refer to FIG. 3(B). When placed on the opening of
sample entrance 26, sample 29 will automatically be sucked into
channel 23 due to the capillarity and/or the hydrophilic
interaction. In addition, FIGS. 3(B) to 3(E) show the flowing
process of sample 29 in channel 23. When sufficient sample 29 is
dropped to the opening of sample entrance 26, sample 29 will flow
along channel 23 as shown in FIGS. 3(C) and 3(D) until totally
covers electrodes 21 and 22 as shown in FIG. 3(E), in the meanwhile
the air in channel 23 is discharged through air hole 28.
[0058] As shown in FIG. 3(B), since sample 29 has not flowed onto
electrode 22 yet, electrodes 22 and 23 are not conducted to each
other and there is no sensing current generated therebetween
although the situation shown in FIG. 3(B) belongs to those of
sample detecting period 101 and the voltage has been applied to the
electrodes.
[0059] In FIG. 3(C), sample 29 has been completely covered
electrode 21 and partially covered electrode 22, and the sensing
current will be generated between electrode 21 and 22 if the
voltage is applied therebetween. At this time, meter 10 needs to
estimate whether the value of the sensing current between
electrodes 21 and 22 achieves sample detecting threshold 112, and
the determination of sample detecting threshold 112 is very
important.
[0060] From FIG. 3(C), it is apparently known that sample 29 does
not fully cover electrode 22. Accordingly, if sample detecting
threshold 112 is too low, the value of the sensing current between
electrodes 21 and 22 under the situation shown in FIG. 3(C) will
achieve sample detecting threshold 112 although sample 29 has not
fully covered electrode 22 yet, so that meter 10 will misjudge and
start the procedures of incubation period 105 and measurement
period 106 and the concentration of the analyte in sample 29
obtained from such these procedures is incorrect. However, if
sample detecting threshold 112 is too high, the value of the
sensing current will not achieve sample detecting threshold 112 and
meter 10 will not start the procedures of incubation period 105 and
measurement period 106 even channel 23 is full of sample 29 as
shown in FIG. 3(D) or 3(E). Moreover, the factors such as the
hematocrit (HCT), or the contents of oxygen, glucose or lipid in
the sample blood will interfere the sensing current, so that the
value of the sensing current may be unable to achieve sample
detecting threshold 112.
[0061] Therefore, the method which can correctively estimate
whether the volume of sample in the reaction region is sufficient
to obtain a correct sensing current is very important for such the
meter.
[0062] Please refer to FIG. 4(A), which shows the schematic diagram
of the internal circuit of the present meter 40 suitable for
electrochemical test strip 20. Although the present meter 40 shown
in FIG. 4(A) and the following figures has an appearance identical
to that of the conventional one, e.g. meter 20, the internal
circuit and the measuring method of the present meter 40 are much
advanced than that of the conventional one.
[0063] As for electrochemical test strip 20 in FIG. 4(A), it has
been illustrated as above and will not repeat in the following
passages.
[0064] FIG. 4(A) shows the internal configuration of meter 40.
Meter 40 has a processor unit 41, a displayer 42, a power supply
unit 43, a current measurement unit 44, a current 45, a
current-to-voltage converter 46, an analog-to-digital convertor 47,
a current buffer 48, a voltage regulator 49, a temperature sensor
410, a strip detecting unit 412 having a switch SW, and a voltage
switching unit 415 having a switch set 420, wherein
current-to-voltage converter 46 is configured in current
measurement unit 44 and used for converting current 45 between
electrodes 21 and 22 into an analog voltage Vo (where
Vo=I.times.Rf). The analog voltage Vo will be converted into an
equivalent digital signal for being calculated by processor unit
41.
[0065] In FIG. 4(A), the divider formed by voltage regulator 49 and
resistors R1 and R2 applies the voltage to contact Vc1, and current
buffer 48 has a capability for driving high current and outputs a
potential identical to that of contact Vc1 at contact Vc2. Under
this situation, the potential of contact 413 is Vw, the potential
of contact 414 is Vc, and a working voltage 411 is Vwc which is
equal to the potential difference between Vw and Vc and applied
between contacts 413 and 414.
[0066] Switch set 420 has four switches S1, S2, S3 and S4, each of
these four switches can be selected from a mechanical relay, an
electronic type of analog switch and a MOSFET or a bipolar
transistor to form a bridge switch for performing the switch. The
voltage switching unit 415 includes a control contact 416 for
receiving the digital control signal transmitted from processor
unit 41, and controlling the turn on/off of switches S1 and S4
accordingly. If the digital control signal received by control
contact 416 is 1, both of switches S1 and S4 will be turned on. On
the contrary, if the digital control signal received by control
contact 416 is 0, both of switches S1 and S4 will turn off.
[0067] Voltage switching unit 415 also includes an inventor 417
which is a basic component of the digital or the logic circuits and
used to reverse the input signal. On the binary logic, if the input
signal is 0, the output signal is 1; and when the input signal is
1, the output signal is 0. Such the principle is used to control
the turn on/off of switches S2 and S3 and makes the time that
switches S2 and S3 are turned off to be always different from that
of switches S1 and S4. In other words, only one of switches S2 and
S3, or switches S1 and S4 can be turned off (turned on) at a
time.
[0068] The control of voltage switching unit 415 is described as
follows. As shown in FIG. 4(B), when processor unit 41 provides a
digital signal 1 to control contact 416, the potentials of output X
and contact 413 are the same since switch S1 is turned on, and the
potentials of output X and contact 413 are Vx and Vw respectively;
and the potentials of output Y and contact 414 are the same since
switch S4 is turned on, and the potentials of output Y and contact
414 are Vy and Vc respectively.
[0069] Since Vx=Vw and Vy=Vc, the potential difference 411 between
outputs X and Y equals to the potential difference Vwc between
contacts 413 and 414. Presently, electrode 21 connected with output
X is the working electrode because of Vx>Vy.
[0070] As shown in FIG. 4(B), when processor unit 41 provides a
digital signal 0 to control contact 416, the potentials of output X
and contact 414 are the same since switch S2 is turned on, and the
potentials of output X and contact 414 are Vx and Vc respectively;
and the potentials of output Y and contact 413 are the same since
switch S3 is turned on, and the potentials of output Y and contact
413 are Vy and Vw respectively.
[0071] Since Vx=Vc and Vy=Vw, the potential difference 411 between
outputs X and Y also equals the potential difference Vwc.
Presently, electrode 22 connected with output Y is the working
electrode because of Vx<Vy.
[0072] FIGS. 5(A) to 5(G) and 6(A) to 6(I) show an embodiment of
the present method, wherein FIGS. 5(A) to 5(G) are partially
amplified diagrams of electrochemical test strip 20. The procedures
of the present method are described as follows.
[0073] (1) Inserting electrochemical test strip 20 into the slot of
meter 40 to turn on switch 412 so as to cause processor unit 41
circularly transmitting digital signals of 1 and 0 to control
contact 416. Presently, the DC voltages of outputs X and Y are
shown as FIGS. 6(A) and 6(C) respectively.
[0074] (2) Then, display 42 shows a request for the supply of
sample 29, typically a blood drop sample.
[0075] (3) When placed on the opening of sample entrance 26
(referring to FIG. 3(A) or 5(A)), sample 29 will automatically be
sucked into channel 23 due to the capillarity and/or the
hydrophilic interaction. FIGS. 5(B) to 5(G) show the flow of sample
29 in channel 23.
[0076] (4) From the time shown in FIG. 5(D), processor unit 41
starts receiving the sensing current generated between the
electrodes of electrochemical test strip 20.
[0077] (A) When the time is 0.about.to, the flow of sample of 29 is
shown as FIGS. 5(B) and 5(C), and the sensing currents respectively
received by outputs X and Y are shown as FIGS. 6(B) and 6(C).
Presently, sample 29 has not flowed onto upper surface 212 of
electrode so that there is no sensing current generated, and the
corresponding cyclic voltammograms is shown as FIG. 6(E).
[0078] (B) When the time is to.about.t2, sample 29 has partially
covered electrode surface 212 as shown in FIG. 5(D), and the
sensing current is initially generated as shown in FIGS. 6(B) and
6(D), wherein the sensing current received by output X has a value
of Ixa, and the sensing current received by output Y has a value of
Iya at this time. Since sample 29 has completely covered upper
surface 211, but only partially covers upper surface 212, so that
Ixa is much greater than Iya. When the time is to.about.t1, the
working voltage is Vwc, the working electrode is electrode 21 and
the area of the working electrode is the whole area of upper
surface 211. When the time is t1.about.t2, the working voltage is
still Vwc, the working electrode is electrode 22 and the area of
the working electrode is the area of upper surface 212 covered by
sample 29. According to the Cottrell Equation, since the sensing
current is proportional to the area of the working electrode, the
sensing current Iya measured during t1.about.t2 is smaller than
that (Ixa) measured during to.about.t1. In addition, the cyclic
voltammograms corresponding to t1.about.t2 is shown as FIG.
6(F).
[0079] (C) When the time is t2.about.t4, sample 29 has more covered
electrode surface 212 as shown in FIG. 5(E), the sensing current
received by output X has a value of Ixb, and the sensing current
received by output Y has a value of Iyb at this time, wherein Ixb
is slightly smaller than Ixa due to the consumption of current
during to.about.t2, but such the difference between Ixb and Ixa is
so minor and can be ignored. In addition, Iyb is greater than Iya
since the area of upper surface 212 covered by sample 29 as shown
in FIG. 5(E) is greater than that shown in FIG. 5(D). Presently,
the corresponding cyclic voltammograms is shown as FIG. 6(G).
[0080] (D) When the time is t4.about.t6, sample 29 has further more
covered electrode surface 212 as shown in FIG. 5(F), the sensing
current received by output X has a value of Ixc, and the sensing
current received by output Y has a value of Iyc at this time,
wherein Ixc is approximately equals to Ixb, and Iyc is greater than
Iyb since the area of upper surface 212 covered by sample 29 as
shown in FIG. 5(F) is greater than that shown in FIG. 5(E).
Presently, the corresponding cyclic voltammograms is shown as FIG.
6(H).
[0081] (E) When the time t6.about.t8, sample 29 has totally covered
electrode surface 212 as shown in FIG. 5(G), the sensing current
received by output X has a value of Ixd, and the sensing current
received by output Y has a value of Iyd at this time, wherein Ixd
is approximately equals to Ixc, Iyd is greater than Iyc, and Ixd is
approximately equals to Iyd since upper surface 212 has been
totally covered by sample 29 as shown in FIG. 5(G) and the
respective areas of upper surfaces 211 and 212 are the same.
Presently, the corresponding cyclic voltammograms is shown as FIG.
6(I).
[0082] (5) Upon processor unit 41 receives the sensing current, it
begins to calculate and estimate whether sample 29 in the reation
region is sufficient. Such the estimation can be preformed via
several ways. For example, processor unit 41 continuously receives
and operates the sensing currents received from outputs X and Y
during a specific period, and then starts the next step, i.e.
starts incubation period 105, upon the ratio of Iy (the sensing
current received from output Y) over Ix (the sensing current
received from output X) greater than or equal to a first
predetermined value, or the ratio of Ix/Iy smaller than or equal to
a second predetermined value; if the ratio of Iy/Ix (or Ix/Iy) can
not achieve the above-mentioned predetermined value after a
predefined period, displayer 42 will show the message of the
insufficiency of the volume of sample (i.e. volume of blood). In
another way, processor unit 41 respectively sums up the received
Ixs and the received Iys, and then starts the next step upon the
ratio of the sum of received Ixs over the sum of received Iys
(Ixs/Iys) is not smaller than (or not greater than) a predetermined
value; if the ratio of Ixs/Iys (or Iys/Ixs) can not achieve the
above-mentioned predetermined value after a predefined period,
displayer 42 will also show the message of the insufficiency of the
volume of sample.
[0083] (6) If processor unit 41 estimates that sample 29 in the
reaction region is sufficient, the standard procedures from
incubation period 105 to measurement period 106 will be performed
to obtain a correct value of sensing current. Processor unit 41
will operates this correct value of sensing current to obtain the
concentration of the target analyte in sample 29, and displayer 42
will show the value of the concentration of the target analyte.
[0084] The preferable range of ratio for estimating the
distribution of sample on the electrodes is obtained from the
experiments of which samples having various volumes are used. The
details of these experiments are described as follows.
[0085] (1) A test strip being suitable for a meter is provided,
wherein the sufficient volume of sample for filling the reaction
region of the test strip is 0.7 .mu.L, the test strip has a first
and a second electrodes, and the area of the first electrode is
smaller than that of the second electrode.
[0086] (2) Then, the samples is driven to flow from the first
electrode to the second electrode, wherein the sample has various
volumes from 0.3 .mu.L to 0.8 .mu.L and such the flowing process of
sample are performed several times.
[0087] (3) Applying a first DC voltage of 0.1V between the first
and the second electrodes for a first duration of 20 ms to cause
the potential of the first electrode higher than that of the second
electrode. The first Cottrell current generated during the first
duration is measured and recorded.
[0088] (4) The first DC voltage is removed for a first removing
duration of 20 ms. Additionally, the removing duration can be 0 ms
to 50 ms upon requests.
[0089] (5) Applying a second DC voltage of 0.1V between the first
and the second electrodes for a second duration of 20 ms to cause
the potential of the second electrode higher than that of the first
electrode. The second Cottrell current generated during the second
duration is measured and recorded. Additionally, the first and the
second durations can be the same or different from each other, and
the range of the two durations is 3 ms to 2 s upon requests.
[0090] (6) The ratio of the first Cottrell current over the second
Cottrell current is calculated.
[0091] Every sample having various volumes are processed according
to the above-mentioned steps (1) to (6) for more than ten times,
where the ranges of ratios for each sample and the coefficient of
variation (CV %) of the first Cottrell current are recorded as
shown in Table 1.
TABLE-US-00001 Range of ratio Coefficient of the first Range of
ratio Average of variation Cottrell of the second value of the (CV
%) of current/the Cottrell first Cottrell the first second
current/the Volume currents Cottrell Cottrell first Cottrell of
sample (.mu.A) current current current 0.3 .mu.L N/A N/A N/A N/A
0.4 .mu.L 2.89 11 0.1-0.5 2.0-10 0.45 .mu.L 3.55 4.52 0.3-0.6
1.6-3.3 0.5 .mu.L 3.85 3.82 0.6-0.9 1.1-1.6 0.6 .mu.L 4.00 2.14
1.0-1.4 0.7-1.0 0.7 .mu.L 3.95 1.39 1.3-1.6 0.6-0.8 (volume for
filling the reaction region) 0.8 .mu.L 3.98 2.05 1.3-1.7
0.6-0.8
[0092] Based on Table 1, it can be realized if the sample volume is
too small, e.g. 0.3 .mu.L, the Cottrell current is unable to be
generated since the sample volume of 0.3 .mu.L is insufficient for
the sample flowing from the first electrode to contact the second
electrode. Although the first Cottrell current can be obtained when
the sample volume is 0.4 .mu.L, the CV % is poor (where CV
%>10%). When the sample volume raises to 0.45 .mu.L to 0.8
.mu.L, the CV % of the first Cottrell current is preferable and
acceptable (where CV %<5%), and the ranges of ratio of the first
Cottrell current/the second Cottrell current, and the second
Cottrell current/the first Cottrell current are 0.3 to 1.7 and 0.6
to 3.3 respectively. In other words, it reveals that the sample has
a preferable distribution/cover within the reaction region of the
test strip if the ratio of the Cottrell currents is between 0.3 to
3.3.
[0093] FIGS. 7(A) and 7(B) show another embodiment of the present
invention, where the configuration of voltage switching unit 715 is
different from that of voltage switching unit 415 as shown in FIG.
4(B). Voltage switching unit 715 receives the control signals
transmitted from processor unit 701 by a control contact 716 and
switches the switches S1, S2 and S3 accordingly, which is described
as follows.
[0094] When S1 and S2 is connected as shown in FIG. 7(A), that:
Vx=Vref=V1=Vr;
Vy=V2=[(R2+R3)/(R1+R2+R3)]Vr; and
Vxy=Vx-Vy=Vr-[(R2+R3)/(R1+R2+R3)]Vr=[R1/(R1+R2+R3)]Vr. Therefore,
Vx>Vy and electrode 21 connected to output X is the working
electrode at this time.
[0095] When S1 and S3 is connected as shown in FIG. 7(B), that:
Vx=V3=[R3/(R1+R2+R3)]Vr;
Vy=V2=[(R2+R3)/(R1+R2+R3)]Vr; and
Vxy=Vx-Vy=[R3/(R1+R2+R3)]Vr-[(R2+R3)/(R1+R2+R3)]Vr=[-R2/(R1+R2+R3)]Vr.
Therefore, Vy>Vx and electrode 22 connected to output Y is the
working electrode at this time.
[0096] If R1 is defined as the same as R2, the voltage differences
Vxy under the mode of S1 connected to S2 and the voltage under the
mode of S1 connected to S3 have the same value and the respective
polarities thereof are inversed.
[0097] Based on this embodiment of switches among switches S1, S2
and S3, the value of sensing current shown in FIGS. 6(A) to 6(I)
can also be obtained accordingly so as to estimate whether the
sample volume is sufficient for the test strip.
[0098] FIG. 8 shows another embodiment of the present invention,
where the configuration of voltage switching unit 815 is different
from those of voltage switching units 415 and 715. In the
embodiment shown in FIG. 8, Vx (voltage on output X) equals to Vr
(voltage on contact 811), and is a constant voltage, and voltage
switching unit 815 receives the control signals transmitted from
processor unit 801, converts the control signal into the analog
voltage by a digital-to-analog voltage converter 816, provides the
analog voltage Vc1 to contact 812 and enhances the output driving
force of the current by a current buffer OP2. At this time, Vy
equals to Vc1 and Vy is adjusted by the control signals of
processor unit 801 to achieve the switch of the voltage. The above
descriptions are further elaborated as follows.
[0099] The absolute value of the working voltage Vxy applied
between outputs X and Y is predetermined as Q.
[0100] Processor unit 801 transmits the digital control signals to
adjust Vc1 at a first time, so that:
Vc1=Vy=Vx-Q; and
Vxy=Vx-Vy=Vx-(Vx-Q)=Q. Therefore, Vx>Vy and electrode 21
connected to output X is the working electrode at this first
time.
[0101] Processor unit 801 transmits the digital control signals to
adjust Vc1 at a second time, so that:
Vc1=Vy=Vx+Q; and
Vxy=Vx-Vy=Vx-(Vx+Q)=-Q. Therefore, Vy>Vx and electrode 22
connected to output Y is the working electrode at this second
time.
[0102] Based on this embodiment that Vc1 is adjusted and switched
according to the digital control signals transmitted from processor
unit 801 at the first and the second times, and the value of
sensing current shown in FIGS. 6(A) to 6(I) can also be obtained
accordingly so as to estimate whether the sample volume is
sufficient for the test strip.
[0103] Through the present invention, when sample enters into
sample entrance 26 and processor units 41, 701 and 801 receives a
sensing current, the sensing current is estimated whether achieves
sample detecting threshold 112. If the sensing current achieves
sample detecting threshold 112, the standard procedures from
incubation period 105 to measurement period 106 are performed. The
switch of voltage as mentioned in the above embodiments can be
performed at any time within incubation period 105 to measurement
period 106, and Ix and Iy are obtained for further operating by
processor units 41, 701 and 801. The effectiveness of the operating
results at or after the end of measurement period is further
confirmed based on the steps disclosed in the above embodiments. In
other words, the present method can be performed at any time within
sample detecting period 101, incubation period 105 and measurement
period 106 to estimate the effectiveness of the operating results
at or after the end of measurement period.
[0104] Please refer to FIGS. 9(A) and 9(B), which show another
embodiment of electrochemical test strip shown in FIG. 2(B), and
9(B) is a sectional drawing of electrochemical test strip 90 taken
along the line B-B'. Electrochemical test strip 90 has two
electrodes 91 and 92 and a reference electrode 93, wherein each of
electrodes 91 and 92 will be the working electrode at a specific
time when the voltage switching unit (415, 715 or 815) operates as
above-mentioned and the Cottrell current is generated accordingly.
When the meter estimates the blood sample volume in electrochemical
test strip 90 as sufficient, reference electrode 93 assists in
further stabilizing predetermined voltage 107 applied to electrodes
91 and 92 during measurement period 106 to obtain a more accurate
sensing current.
[0105] FIGS. 10(A) to 10(D) and FIGS. 11(A) to 11(C) respectively
show electrochemical test strips 1001 and 1101, each of which has
the thin-film electrodes. FIGS. 10(C) and (D) are sectional
drawings of electrochemical test strip 1001 taken along the line
C-C'. FIG. 11(C) is a sectional drawing of electrochemical test
strip 1101 taken along the line D-D'. The formations and the
structures of electrochemical test strips 1001 and 1101 are
disclosed in U.S. Pat. No. 5,997,817, U.S. Pat. No. 5,985,116 and
EP 1098000, and thin film electrodes 1002, 1003, 1102, 1103 and
1104 can be formed by the screen printing or the metal
deposition.
[0106] As shown in FIG. 10(C), when a blood sample 1008 starts to
flow into channel 1010 of electrochemical test strip 1001 from
sample entrance 1009, there will no sensing current be generated.
However, with blood sample 1008 further flowing to cover electrode
1002 and contact electrode 1003 as shown in FIG. 10(D), the value
of sensing current shown in FIGS. 6(A) to 6(I) can also be obtained
accordingly so as to estimate whether the sample volume is
sufficient for electrochemical test strip 1001.
[0107] A preferable embodiment is shown in FIGS. 11(A) to 11(C),
where electrochemical test strip 1101 has a third thin-file
electrode 1104 which is a thin-film reference electrode. Based on
the present methods as above-mentioned, the value of sensing
current shown in FIGS. 6(A) to 6(I) can also be obtained
accordingly so as to estimate whether the sample volume is
sufficient for electrochemical test strip 1101.
[0108] While the disclosure has been described in terms of what is
presently considered to be the most practical and preferred
embodiments, it is to be understood that the disclosure needs not
be limited to the disclose embodiments. Therefore, it is intended
to cover various modifications and similar arrangements included
within the spirit and scope of the appended claims, which are to be
accorded with the broadest interpretation so as to encompass all
such modifications and similar structures.
* * * * *