U.S. patent application number 10/326008 was filed with the patent office on 2004-06-24 for analyte test intrument having improved versatility.
Invention is credited to Karinka, Shridhara Alva, Sanghera, Gurdial, Wang, Yi.
Application Number | 20040118704 10/326008 |
Document ID | / |
Family ID | 32593915 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040118704 |
Kind Code |
A1 |
Wang, Yi ; et al. |
June 24, 2004 |
Analyte test intrument having improved versatility
Abstract
An analyte test instrument that has a test strip circuitry that
can be configured using information provided by a calibration strip
to perform assays with test strips having two electrodes and test
strips having three electrodes. The analyte test instrument of this
invention comprises: (a) a test port for receiving a test strip;
(b) a microprocessor for executing instructions downloaded into the
analyte test instrument; (c) a test strip circuit capable of having
a plurality of configurations, the configurations being set by the
microprocessor, whereby an assay can be performed using the test
strip.
Inventors: |
Wang, Yi; (Southborough,
MA) ; Karinka, Shridhara Alva; (Lowell, MA) ;
Sanghera, Gurdial; (Oxon, GB) |
Correspondence
Address: |
STEVEN F. WEINSTOCK
ABBOTT LABORATORIES
100 ABBOTT PARK ROAD
DEPT. 377/AP6A
ABBOTT PARK
IL
60064-6008
US
|
Family ID: |
32593915 |
Appl. No.: |
10/326008 |
Filed: |
December 19, 2002 |
Current U.S.
Class: |
205/792 ;
204/403.01 |
Current CPC
Class: |
G01N 33/48785 20130101;
G01N 27/3272 20130101; G01N 27/3273 20130101; G01N 33/48771
20130101 |
Class at
Publication: |
205/792 ;
204/403.01 |
International
Class: |
G01N 027/26 |
Claims
What is claimed is:
1. An analyte test instrument suitable for performing an assay with
a test strip, said analyte test instrument comprising: (a) a test
port for receiving a test strip; (b) a microprocessor for executing
instructions downloaded into said instrument; and (c) a test strip
circuit capable of having a plurality of configurations, said
configurations being set by said microprocessor, whereby an assay
can be performed using said test strip.
2. The analyte test instrument of claim 1, further including a
memory for storing instructions and information.
3. The analyte test instrument of claim 2, wherein said
instructions are selected from the group consisting of measurement
delay time(s), sample incubation time(s), number of measurements to
be taken during an assay, threshold(s) against which voltage
level(s) can be compared, value(s) of excitation voltage level(s)
applied to a test strip during an assay, analyte value conversion
factors, failsafe assay threshold value(s), and configurations of
said test strip circuit of said analyte test instrument.
4. The analyte test instrument of claim 2, wherein said test port
is capable of receiving a calibration strip, said calibration strip
being removable from said test port to allow a test strip to be
inserted into said test port.
5. The analyte test instrument of claim 1, wherein at least one of
said plurality of configurations can be used to perform an assay
with a test strip having two electrodes.
6. The analyte test instrument of claim 1, wherein at least one of
said plurality of configurations can be used to perform an assay
with a test strip having three electrodes.
7. The analyte test instrument of claim 1, further comprising a
push button.
8. The analyte test instrument of claim 1, further comprising a
display.
9. The analyte test instrument of claim 1, wherein said test port
comprises two sets of electrical contacts, whereby a first set of
electrical contacts engages a first major surface of a test strip
and a second set of electrical contacts engages a second major
surface of said test strip.
10. The analyte test instrument of claim 1, wherein said test strip
is capable of performing an assay for determining concentration of
an analyte in a biological sample, said analyte selected from the
group consisting of glucose, lactate, and ketone bodies.
11. A method for determining the concentration of at least one
analyte in a biological sample, said method comprising the steps
of: (a) providing said analyte test instrument of claim 1; (b)
inserting a test strip into said test port of said analyte test
instrument; (c) applying a biological sample to said test strip;
(d) allowing said analyte test instrument to set said configuration
of said test strip circuit to a mode suitable for performing said
determination; and (e) measuring an electrical response provided by
said test strip by means of said test strip circuit.
12. The method of claim 11, wherein said configurations include a
first configuration, said first configuration for use with a test
strip having two electrodes, and a second configuration, said
second configuration for use with a test strip having three
electrodes.
13. The method of claim 11, further including the step of allowing
said analyte test instrument to identify said test strip when said
test strip is inserted into said test port.
14. The method of claim 13, wherein said identification step is
performed by having electrical contacts located in said test port
interact or fail to interact with electrically conductive material
applied to at least one major surface of said test strip.
15. The method of claim 13, wherein said identification step
indicates the analyte to be determined with said test strip.
16. The method of claim 11, wherein said microprocessor converts
said electrical response provided by said test strip into a value
that represents the concentration of said analyte.
17. The method of claim 16, further including the step of reporting
said concentration of said analyte to a user of said analyte test
instrument.
18. The method of claim 11, further including the step of
calibrating said analyte test instrument for each of a plurality of
assays that can be performed with said analyte test instrument.
19. The method of claim 18, wherein said calibration step is
performed with a calibration strip that has been inserted into said
test port.
20. The method of claim 19, further including the step of providing
instructions during said calibration step for effecting the
switching of said configuration of said test strip circuit from a
first configuration, said first configuration for use with a test
strip having two electrodes, and a second configuration, said
second configuration for use with a test strip having three
electrodes.
21. The method of claim 20, wherein said instruction providing step
is performed with a calibration strip inserted into said test
port.
22. The method of claim 11, further including the step of
calibrating said analyte test instrument for each of a plurality of
assays, said calibration step involving (a) insertion of a
calibration strip into a port in said analyte test instrument, said
calibration strip containing instructions for switching the test
strip circuit configuration from a first mode to a second mode
during said determination, said instructions capable of being
downloaded into said analyte test instrument, and (b) removal of
said calibration strip from said test port.
23. The method of claim 11, wherein said analyte is selected from
the group consisting of glucose, lactate, and ketone bodies.
24. An analyte test instrument suitable for performing an assay
with a test strip, said analyte test instrument comprising: (a) a
test port for receiving a test strip; (b) a microprocessor for
executing instructions downloaded into said instrument; and (c) a
test strip circuit capable of having a plurality of configurations,
said configurations being set by said microprocessor, wherein at
least one of said instruction enables said microprocessor to switch
configuration of said test strip circuit during an assay.
25. The analyte test instrument of claim 24, further including a
memory for storing instructions and information.
26. The analyte test instrument of claim 25, wherein said
instructions are selected from the group consisting of measurement
delay time(s), sample incubation time(s), number of measurements to
be taken during an assay, threshold(s) against which voltage
level(s) can be compared, value(s) of excitation voltage level(s)
applied to a test strip during an assay, analyte value conversion
factors, failsafe assay threshold value(s), and configurations of
said test strip circuit of said analyte test instrument.
27. The analyte test instrument of claim 25, wherein said test port
is capable of receiving a calibration strip, said calibration strip
being removable from said test port to allow a test strip is
inserted into said test port.
28. The analyte test instrument of claim 24, wherein at least one
of said plurality of configurations can be used to perform an assay
with a test strip having two electrodes.
29. The analyte test instrument of claim 24, wherein at least one
of said plurality of configurations can be used to perform an assay
with a test strip having three electrodes.
30. The analyte test instrument of claim 24, further comprising a
push button.
31. The analyte test instrument of claim 24, further comprising a
display.
32. The analyte test instrument of claim 24, wherein said test port
comprises two sets of electrical contacts, whereby a first set of
electrical contacts engages a first major surface of a test strip
and a second set of electrical contacts engages a second major
surface of said test strip.
33. The analyte test instrument of claim 24, wherein said test
strip is capable of performing an assay for determining
concentration of an analyte in a biological sample, said analyte
selected from the group consisting of glucose, lactate, and ketone
bodies.
34. A method for determining the concentration of at least one
analyte in a biological sample, said method comprising the steps
of: (a) providing the analyte test instrument of claim 24; (b)
inserting a test strip into said test port of said analyte test
instrument; (c) applying a biological sample to said test strip;
(d) allowing said analyte test instrument to set said configuration
of said test strip circuit to a mode suitable for performing said
determination; and (e) measuring an electrical response provided by
said test strip by means of said test strip circuit.
35. The method of claim 34, wherein said configurations include a
first configuration, said first configuration for use with a test
strip having two electrodes, and a second configuration, said
second configuration for use with a test strip having three
electrodes.
36. The method of claim 34, further including the step of allowing
said analyte test instrument to identify said test strip when said
test strip is inserted into said test port.
37. The method of claim 36, wherein said identification step is
performed by having electrical contacts located in said test port
interact or fail to interact with electrically conductive material
applied to at least one major surface or said test strip.
38. The method of claim 36, wherein said identification step
indicates the analyte to be determined with said test strip.
39. The method of claim 34, wherein said microprocessor converts
said electrical response provided by said test strip into a value
that represents the concentration of said analyte.
40. The method of claim 39, further including the step of reporting
said concentration of said analyte to a user of said analyte test
instrument.
41. The method of claim 34, further including the step of
calibrating said analyte test instrument for each of a plurality of
assays that can be performed with said analyte test instrument.
42. The method of claim 41, wherein said calibration step is
performed with a calibration strip that has been inserted into said
test port.
43. The method of claim 42, further including the step of providing
instructions during said calibration step for effecting the
switching of said configuration of said test strip circuit from a
first configuration, said first configuration for use with a test
strip having two electrodes, and a second configuration, said
second configuration for use with a test strip having three
electrodes.
44. The method of claim 43, wherein said instruction providing step
is performed with a calibration strip inserted into said test
port.
45. The method of claim 34, further including the step of
calibrating said analyte test instrument for each of a plurality of
assays, said calibration step involving (a) insertion of a
calibration strip into a port in said analyte test instrument, said
calibration strip containing instructions for switching the test
strip circuit configuration from a first mode to a second mode
during said determination, said instructions capable of being
downloaded into said analyte test instrument, and (b) removal of
said calibration strip from said test port.
46. The method of claim 34, wherein said analyte is selected from
the group consisting of glucose, lactate, and ketone bodies.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to analyte test instruments that
perform electrochemical assays on biological samples. More
particularly, the invention relates to analyte test instruments
that can perform electrochemical assays by using different modes of
operation.
[0003] 2. Discussion of the Art
[0004] Electrochemical assays for determining the concentrations of
analytes in samples comprising complex mixtures of liquids have
been developed. Such electrochemical assays can be performed with
test strips, i.e., biosensors in the form of strips. Test strips
can function in an invasive manner (i.e., as probes that come into
contact with a body fluid, such as whole blood or subcutaneous
fluid). Test strips can function in a non-invasive manner (i.e., as
strips that come into contact with blood withdrawn by a syringe or
a lancing device). In particular, test strips for biomedical
applications (e.g., whole blood analyses) have been developed for
the determination of glucose levels in biological samples.
[0005] An analyte test instrument is an instrument can be used to
perform electrochemical assays to determine the concentration of an
analyte (e.g., glucose) in a biological sample (e.g., blood). To
operate such an instrument, a user inserts a test strip into a test
port in the instrument. The instrument displays a "ready"
indication to the user and allows sufficient time for the user to
deposit a biological sample on the test strip. When a sufficient
quantity of the sample reaches the working electrode of the test
strip, an electrochemical reaction occurs. The reaction produces an
electrical response, such as a change in current. The electrical
response is detectable by the analyte test instrument. The analyte
test instrument converts the detected signal into data that
corresponds to information relating to the analyte and displays the
information to the user. The instrument may be able to store a
series of such measurements and provide the stored information to
the user via a display or to an external processor via a data
link.
[0006] All commercially available electrochemical assays employing
test strips for determining the concentration of glucose employ
test strips having two electrodes. See, for example, WO 99/19507,
incorporated herein by reference, which describes a test strip
having two electrodes. In a test strip having two electrodes, the
test strip has (1) a working electrode and (2) a dual-purpose
reference/counter electrode. The reaction that takes place at the
working electrode is the reaction that is required to be monitored
and controlled. The second electrode is called a dual-purpose
reference/counter electrode because this electrode acts as a
reference electrode as well as a counter electrode. No current
passes through an ideal reference electrode, and such an electrode
maintains a steady potential; current does pass through a
dual-purpose reference/counter electrode, and thus, the
dual-purpose reference/counter electrode does not maintain a steady
potential during the measurement. At low currents and/or at short
durations of time for measurement, the shift in potential is small
enough such that the response at the working electrode is not
significantly affected, and hence the dual-purpose
reference/counter electrode is designated a dual-purpose
reference/counter electrode. The dual-purpose reference/counter
electrode continues to carry out the function of a counter
electrode; however, in this case, the potential that is applied
between the dual-purpose reference/counter electrode and the
working electrode cannot be altered to compensate for changes in
potential at the working electrode.
[0007] Electrochemical assays employing test strips having three
electrodes employ a test strip having (1) a working electrode, (2)
a reference electrode, and (3) a counter electrode. See, for
example, U.S. Ser. No. 10/062,313, filed Feb. 1, 2002, incorporated
herein by reference. As in the test strip having two electrodes,
the reaction that takes place at the working electrode is the
reaction that is required to be monitored and controlled. The
functions of the reference electrode and the counter electrode are
to ensure that the working electrode actually experiences the
conditions desired, i.e. the correct potential intended to be
applied. The function of the reference electrode is to measure the
potential at the interface of the working electrode and the sample
as accurately as possible. In an ideal situation, no current passes
through the reference electrode. The function of the counter
electrode is to ensure that the correct potential difference
between the reference electrode and the working electrode is being
applied. The potential difference between the working electrode and
the reference electrode is assumed to be the same as the desired
potential at the working electrode. If the potential measured at
the working electrode is not the potential desired at the working
electrode, the potential that is applied between the counter
electrode and the working electrode is altered accordingly, i.e.,
the potential is either increased or decreased. The reaction at the
counter electrode, as measured by the current, is also equal and
opposite to the charge transfer reaction, as measured by the
current, occurring at the working electrode, i.e., if an oxidation
reaction is occurring at the working electrode then a reduction
reaction will take place at the counter electrode, thereby allowing
the sample to remain electrically neutral.
[0008] An analyte test instrument designed for test strips having
two electrodes could not be used if an assay employing a test strip
having three electrodes needs to be performed. The user would have
to use a separate analyte test instrument. If the user wanted to
perform a set of assays that required strips having two electrodes
and a set of assays that required strips having three electrodes,
these assays could not be performed on the same analyte test
instrument.
[0009] An analyte test instrument for electrochemical assays often
requires the user to calibrate the instrument for each batch of
test strips. U.S. Pat. No. 5,366,609, incorporated herein by
reference, describes a calibration technique that requires a
read-only-memory (ROM) key for operation and calibration of an
analyte test instrument. A ROM key is inserted into a port (i.e.,
the ROM key port) that is distinct from the port for a test strip
(i.e., the test port). A test strip is inserted into the test port
after the ROM key is inserted into the ROM key port. The ROM key
must remain in the ROM key port during both the calibration and the
operation of the instrument. The ROM key contains specific data,
including algorithms, for carrying out procedures for determining
the concentration of an analyte in a biological sample applied to
one of a batch of test strips associated with the ROM key. The data
stored in the ROM key include measurement delay times, incubation
times, the number of measurements to be taken during a measurement
period, various thresholds against which voltage levels can be
compared, values of excitation voltage levels applied to the strip
during a test procedure, glucose value conversion factors, and a
variety of failsafe test threshold values. In addition, the ROM key
can contain some or all of the code for the microprocessor that
controls the performing of the assay. A microprocessor in the
analyte test instrument uses the algorithms, the conversion
factors, and the code provided by the ROM key as needed.
[0010] U.S. Pat. No. 6,377,894, incorporated herein by reference,
describes an instrument requiring a ROM key for operation and
calibration of the instrument. The ROM key is inserted into the
test port of the instrument and data is downloaded from the ROM key
by the instrument and stored in the memory of the instrument. The
ROM key contains data needed for carrying out procedures for
determining the concentration of an analyte in a biological sample
applied to a test strip. The ROM key is removed so that test strips
can be inserted into the test port to perform assays. Different ROM
keys can be inserted into the instrument to provide data for the
testing of different analytes on the same instrument. The
instrument can communicate with the ROM key to determine the
analyte for which the ROM key contains information. Calibration
information can be stored in different locations in the memory of
the instrument for each analyte the instrument is capable of
testing. When a test strip is inserted into the test port, the
instrument has the ability to recognize which analyte is being
tested. The microprocessor in the instrument then recalls the
instructions for carrying out procedures for determining the
concentration of that analyte, and the instrument then performs the
appropriate test.
[0011] The aforementioned patents do not describe how the
electrical circuitry of the instrument can be reconfigured so that
analytical tests that require different circuit configurations can
be performed on the same instrument. The aforementioned patents do
not describe how stored information relating to the configuration
of the electrical circuitry of the instrument can be modified when
an assay for a specific analyte needs to be modified. The
aforementioned patents do not describe how stored information can
be used to reconfigure the electrical circuitry of the instrument
while a test strip is being used. Accordingly, it would be
desirable to provide an analyte test instrument that addresses the
foregoing deficiencies.
SUMMARY OF THE INVENTION
[0012] In one aspect, this invention provides an analyte test
instrument that has test strip circuitry that can be placed into
different configurations by means of information provided by a
calibration strip to perform assays with test strips having two
electrodes and test strips having three electrodes. In another
aspect, this invention provides methods for using the analyte test
instrument to perform assays with test strips having two electrodes
and test strips having three electrodes. The analyte test
instrument of this invention comprises:
[0013] (a) a test port for receiving a test strip;
[0014] (b) a microprocessor for executing instructions downloaded
into the instrument; and
[0015] (c) a test strip circuit capable of having a plurality of
configurations, the configurations being set by the microprocessor,
whereby an assay can be performed using a test strip that has been
inserted into the test port.
[0016] In preferred embodiments, the analyte test instrument
further includes a memory for storing instructions and information
required for the operation of the instrument. However, in other
embodiments, the memory can be removably attached to the
instrument, as described previously in U.S. Pat. No. 5,366,609.
[0017] In one embodiment, the invention provides an analyte test
instrument that can perform assays on a variety of different
analytes. In order to perform these assays, a calibration strip is
inserted into the test port. After communication is established
between the calibration strip and the analyte test instrument,
information (i.e., data or programs or both) involving the
method(s) for performing the assay(s) are downloaded from the
calibration strip, and, if the analyte test instrument has a
memory, preferably stored in the memory of the analyte test
instrument. In the analyte test instrument having a memory, the
information is stored in the analyte test instrument after the
calibration strip is removed. The stored information specifies
whether the method(s) of the assay(s) requires a test strip having
two electrodes or test strip having three electrodes.
[0018] In the performance of an assay, a test strip is inserted
into the test port, and the identity of the assay is indicated,
preferably by means of a pattern of conductive material applied to
a major surface of the test strip, preferably the major surface
that does not support the electrodes. The analyte test instrument
then determines from the downloaded information whether the assay
calls for a test strip having two electrodes or for a test strip
having three electrodes. The appropriate electrical switches in the
test strip circuit of the analyte test instrument are then opened
or closed to establish the configuration of the test strip circuit
appropriate for the test strip utilized in the assay, that is, a
test strip having two electrodes or a test strip having three
electrodes. A sample to be analyzed, typically a biological sample,
is then applied to the test strip, and a reaction that generates an
electrical response occurs. The electrical response is detected and
measured by the analyte test instrument, and the concentration of
the analyte tested is determined by means of the downloaded
calibration information. The analyte test instrument then displays
the concentration of the analyte. Assays that call for a test strip
having two electrodes and assays that call for a test strip having
three electrodes can be performed on the same analyte test
instrument.
[0019] In another embodiment, the analyte test instrument of this
invention features the capability of changing the method for
performing an assay to determine the concentration of a particular
analyte. In order to change the method for performing the assay, a
new calibration strip is inserted into the test port. The
instructions for the performing the new method of the assay for the
particular analyte are then downloaded to the analyte test
instrument, and, if the analyte test instrument has a memory,
preferably stored in the memory of the analyte test instrument.
When the test strip is inserted into the test port, the identity of
the assay is determined. The appropriate electrical switches in the
test strip circuit of the analyte test instrument are then opened
or closed to establish the appropriate circuit configuration for
the test strip utilized in the assay, that is, a test strip having
two electrodes or a test strip having three electrodes. The circuit
configurations are based on the information from the calibration
strip most recently downloaded to the analyte test instrument. The
same analyte test instrument can be used to perform an assay even
if the test method is changed one employing a test strip having two
electrodes to one employing a test strip having three electrodes,
and vice versa.
[0020] In another embodiment of this invention, the analyte test
instrument can employ both a two-electrode mode and a
three-electrode mode during the same assay. The expression
"two-electrode mode" refers to the test strip circuitry employed
for operating an analyte test instrument with a test strip having
two electrodes. The expression "three-electrode mode" refers to the
test strip circuitry employed for operating an analyte test
instrument with a test strip having three electrodes. The
information previously downloaded from the calibration strip, and,
preferably, stored in the memory of the analyte test instrument,
specifies what portion of the assay employs a test strip circuit
configuration in a two-electrode mode and what portion of the assay
employs a test strip circuit configuration in a three-electrode
mode. A test strip is inserted into the test port, and the identity
of the assasy is indicated, preferably from a pattern of conductive
material that has been applied to a major surface of the test
strip, preferably the major surface that does not support the
electrodes. The analyte test instrument then determines from the
aforementioned downloaded information whether the assay requires a
test strip circuit configuration in a two-electrode mode or a test
strip circuit configuration in a three-electrode mode at the start
of the assay. The appropriate electrical switches in the analyte
test instrument are then opened or closed to establish the
appropriate electrode mode. A sample to be analyzed, typically a
biological sample, is then applied to the test strip, and a
reaction that generates an electrical response occurs. During the
performance of the assay, the appropriate electrical switches in
the analyte test instrument are then opened or closed to establish
the test strip circuit configuration for the appropriate electrode
mode, which is a different electrode mode than was used at the
start of the assay. The electrical response is detected and
measured by the analyte test instrument, and the concentration of
the analyte is determined by means of the downloaded calibration
information. The analyte test instrument can then display the
concentration of the analyte.
[0021] One example wherein the test strip circuit configuration is
switched during an assay involves an assay in which it may be
preferred to use a test strip having three electrodes for the
advantages provided by the use of a test strip having three
electrodes, such as, for example, improved control of voltage at
the working electrode. However, it may be desired to exclude the
working electrode of the test strip having three electrodes during
the sample detection phase of the assay. In this case, the test
strip circuit for the two-electrode mode is preferred during this
sample detection phase of the assay. Accordingly, test strip
circuit configurations for both the two-electrode mode and the
three-electrode mode are desired within the course of an assay. It
is assumed that an assay involves operational steps beginning with
the insertion of the test strip into the analyte test instrument
and obtaining the result of the assay.
[0022] The analyte test instrument of this invention makes it
possible for the user to perform assays with test strips having two
electrodes and test strips having three electrodes with the same
instrument. The analyte test instrument of this invention makes it
possible for an assay to be modified without having to discard the
instrument. The analyte test instrument of this invention makes it
possible for the mode of operation to change during the performance
of an assay without intervention from the user.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a perspective view of an embodiment of an analyte
test instrument suitable for use in this invention.
[0024] FIG. 2 is a block diagram that illustrates electronic
components of an analyte test instrument suitable for use in this
invention.
[0025] FIG. 3A is a perspective view of a test strip that is
suitable for use with the analyte test instrument of this
invention.
[0026] FIG. 3B is a perspective view of a calibration strip that is
suitable for use with the analyte test instrument of this
invention.
[0027] FIG. 4A illustrates a top plan view of test strip that is
suitable for use with the analyte test instrument of this
invention.
[0028] FIG. 4B illustrates a bottom plan view of test strip that is
suitable for use with the analyte test instrument of this
invention.
[0029] FIG. 5 is a flow chart illustrating a method for calibrating
the analyte test instrument of this invention.
[0030] FIG. 6 is a flow chart illustrating a method for calibrating
the analyte test instrument of this invention.
[0031] FIGS. 7A, 7B, and 8 are schematic diagrams that illustrates
a test strip circuit that can be used to perform assays with two
different types of test strips.
DETAILED DESCRIPTION
[0032] As used herein, the expression "test strip having two
electrodes" and other expressions relating to tests strips having
two electrodes refer to test strips that have a working electrode
and a dual-purpose reference/counter electrode. The expression
"test strip having three electrodes" and other expressions relating
to tests strips having three electrodes refer to test strips that
have a working electrode, a counter electrode, and a reference
electrode, the reference electrode being separate from the counter
electrode. A "test strip having two electrodes" can have one or
more additional electrodes, so long as the strip has a dual-purpose
reference/counter electrode that performs the functions of both a
reference electrode and a counter electrode. For example, a test
strip having two electrodes can have a trigger electrode, which is
an electrode that detects when a sufficient quantity of sample has
been applied to the test strip. A "test strip having three
electrodes" can have one or more additional electrodes, so long as
the test strip has one electrode for performing the function of a
reference electrode and another electrode for performing the
function of a counter electrode. For example, a test strip having
three electrodes can have a dummy electrode, which is an electrode
that is similar to the working electrode, but lacks the substance
that reacts with the analyte (see, for example, U.S. Pat. No.
5,628,890), or a trigger electrode dedicated to the sole function
of detecting when a sufficient quantity of sample has been applied
to the test strip (see, for example, U.S. Pat. No. 5,582,697).
[0033] As stated previously, all commercially available
electrochemical test strips for determining the concentration of
glucose employ two electrodes--(1) a working electrode and (2) a
dual-purpose reference/ counter electrode. As stated previously,
electrochemical systems having three electrodes employ (1) a
working electrode, (2) a reference electrode, and (3) a counter
electrode.
[0034] Electrochemical systems employing test strips having three
electrodes have the requirement that little or no current pass
between the working electrode and the reference electrode. This
requirement is achieved by using high impedance operational
amplifiers in the electrical circuits of these systems. High
impedance operational amplifiers are expensive; consequently,
electrochemical systems that perform assays with test strips having
three electrodes are expensive. These expensive systems are
generally used only in research and are not practical from a cost
standpoint for use by diabetics for glucose monitoring at home.
[0035] A test strip having three electrodes would be preferred in
any electrochemical measurement that involves the application of an
external voltage and measurement of current. However, due to
constraints of sample volume (lower volume requirements), all
electrochemical test strips commercially available use only two
electrodes. Precise control of the voltage difference between the
working electrode and the reference electrode must be maintained,
but such control is difficult to achieve in a test strip having two
electrodes. In known analyte test instruments, the electrical
components of an analyte test instrument designed for test strips
employing two electrodes would not operate with test strips
employing three electrodes.
[0036] Referring now to FIG. 1, an analyte test instrument 100
comprises a housing 102, which contains the electrical and
electronic components of the analyte test instrument. The analyte
test instrument 100 comprises a test port 110, a push button 120,
and a display 130. The test port 110 is a multi-purpose test port,
which comprises a slot into which a user inserts test strips and
calibration strips. The test port 110 comprises a slot assembly
capable of receiving a strip, such as a test strip or a calibration
strip. The test port 110 can have a plurality of electrical
contacts capable of electrically engaging such a strip when the
strip is inserted into the test port 110. The push button 120
allows the user to control the analyte test instrument 100. In
particular, the push button 120 is used to turn the instrument on
and off, to recall information stored in the instrument, to respond
to messages displayed, and to set some of the configuration control
parameters for the instrument. The push button 120 can also provide
access to menus generated by software contained in the analyte test
instrument 100. The display 130 is a device that gives information
in a visual form. The display 130 is typically a screen. The
information given typically includes, but is not limited to, test
results, messages to the user, information stored in the memory of
the analyte test instrument.
[0037] In one embodiment, one or more replaceable batteries (not
shown) installed via a battery compartment at the rear of the
analyte test instrument 100 (not shown) provide power for the
analyte test instrument 100. It should be understood, however, that
any source of power capable of providing a suitable direct (DC)
voltage can provide power to the analyte test instrument 100.
[0038] FIG. 2 is a block diagram that shows the interrelationship
among the electronic components of an analyte test instrument 100.
In addition to the aforementioned test port 110, push button 120,
and display 130, all of which are accessible from the exterior of
the analyte test instrument 100, the analyte test instrument 100
comprises a processing circuit 210, at least one device circuit
212, at least one test strip circuit 214, a microprocessor 216, and
a memory 218.
[0039] The purpose of the processing circuit 210 is to enable a
strip that is engaged in the test port 110 to communicate with the
microprocessor 216 and the memory 218. For example, the processing
circuit 210 can send signals to the test port 110 to determine the
identity of the strip inserted therein, i.e., to determine whether
the strip is a calibration strip or a test strip.
[0040] The device circuit(s) 212 and the test strip circuit(s) 214
can comprise analog, digital, or mixed-signal circuits,
application-specific integrated circuits (ASICS), and passive and
active electrical components. The device circuit(s) 212 can perform
various electrical functions required by the analyte test
instrument 100, such as driving the display function 130 and the
clock functions for a microprocessor 216. In other words, the
device circuit(s) carries instructions from the microprocessor 216
to various functional components of the analyte test instrument 100
so that these components can perform their intended functions. Test
strip circuit(s) 214 can perform analog-to-digital (A/D) conversion
of signals received at the test port 110 from a test strip and can
perform digital-to-analog (D/A) conversion of signals received from
the microprocessor 216. In other words, the test strip circuit(s)
transmits information between the microprocessor 216 and the test
strip. For example, the test strip circuit(s) is used to ensure
that the proper voltage is being applied to the test strip and that
the proper value of current generated at the test strip is being
measured by the microprocessor 216.
[0041] The microprocessor 216 is an integrated circuit that
contains the entire central processing unit of a computer. The
memory 218 is a unit of a computer that preserves information for
the purpose of retrieval. Such information may include, but is not
limited to, measurement delay time(s), sample incubation time(s),
number of measurements to be taken during an assay, threshold(s)
against which voltage level(s) can be compared, value(s) of
excitation voltage level(s) applied to a test strip during an
assay, analyte value conversion factors, failsafe assay threshold
value(s), and configurations of circuitry of the analyte test
instrument.
[0042] In a preferred embodiment, the memory 218 comprises at least
1K of random access memory (RAM). In more preferred embodiments,
the memory 218 has sufficient additional capacity to store a
multiplicity of assay results.
[0043] Instrument software 220 is responsive to information
received at the test port 110 from a calibration strip. The
instrument software 220 uses the information received to control
the operation of the analyte test instrument 100. the instrument
software 220 also controls operations of the analyte test
instrument 100 that are independent of information introduced or
generated at the test port 110. For example, the instrument
software 220 can enable the user to recall assay results and assay
information, can provide various warning, error, and prompting
messages, can permit setting of date and time, can control
transmission of data to external devices, can monitor power level
or battery level or both, and can provide indications to the user
if power drops below a specified level.
[0044] In the embodiment illustrated in FIG. 2, the test port 110
includes six electrical contacts, which are labeled IDENT1, IDENT2,
IDENT3, SENS1, SENS2, and SENS3. When a strip is inserted into the
test port 110, the major surfaces of the strip engage the
electrical contacts of the test port 110, thereby enabling the
analyte test instrument 110 to identify a pattern of conductive
material on the top major surface of the strip, on the bottom major
surface of the strip, or on both major surfaces of the strip. In a
preferred embodiment, the pattern of conductive material on an
inserted strip that interacts with the electrical contacts IDENT1,
IDENT2, and IDENT3 indicates whether the inserted strip is a
calibration strip or a test strip. This embodiment is shown in
FIGS. 4A and 4B, which will be described later. If the inserted
strip is a test strip, the type of analyte to be determined by the
assay to be performed with the test strip is also identified (e.g.,
glucose, ketone bodies, etc.). The engagement of the electrical
contacts and the strip identification process are described in more
detail in U.S. Pat. No. 6,377,894, incorporated herein by
reference. The electrical contacts labeled SENS1, SENS2, and SENS3
relate to the electrodes that are involved in performing analytical
tests.
[0045] FIG. 3A illustrates in more detail a test strip 230. A
plurality of electrical contacts 232 is provided at the end 234 of
the test strip 230 that is inserted into the test port 110. Upon
insertion of the test strip 230 into the test port 110, the
electrical contacts 232 contact the electrical contacts SENS1,
SENS2, and SENS3. Typically, a sample, e.g., a drop of blood,
undergoing the assay is placed for testing on the reaction area 236
of the test strip 230. The reaction area 236 is the area where the
sample contacts the electrodes of the test strip 230 (i.e., the
working electrode and the dual purpose reference/counter electrode
in the strip having two electrodes and the working electrode, the
reference electrode, and the counter electrode in the strip having
three electrodes). When a sufficient quantity of sample is
deposited on the reaction area 236, an electrochemical reaction
occurs, whereby a flow of electrons produces an electrical
response, such as a change in current. The response is detectable
by the analyte test instrument 100. The analyte test instrument 100
converts the detected response into data that is correlated with
information relating to the analyte and displays the information to
the user.
[0046] FIG. 3B illustrates a ROM-type calibration strip 240. In one
embodiment, a ROM-type calibration strip 240 is associated with a
package (not shown) of test strips 230. A plurality of electrical
contacts 242 is provided at the end 244 of the calibration strip
240 that is inserted into the test port 110. In one embodiment, the
calibration code 246 and manufacturing lot number 248 are printed
on the calibration strip 240 and are visible to the user. In
another embodiment, the lot number is stored in a read-only-memory
(ROM) 250 in binary coded decimal (BCD) format.
[0047] The ROM 250, which is in electrical communication with the
electrical contacts 242, encodes information relating to
algorithm(s) for processing data obtained in an assay with a test
strip. The ROM 250 can also encode information relating to the
calibration code 246 and manufacturing lot number 248 as well as
other parameters, as described in U.S. Pat. No. 6,377,894,
incorporated herein by reference. The assays are not performed with
the calibration strip 240. Rather, the calibration strip 240
delivers the information, the algorithms, the parameters, and the
procedures that are required to characterize an assay to the
analyte test instrument 100. The ROM 250 is capable of storing and
downloading to the analyte test instrument 100 parameters that
characterize an assay as having a two-electrode format or a
three-electrode format.
[0048] Referring to FIGS. 4A and 4B, a test strip 400 has a pattern
of conductive material 402 on the major surface 404 thereof that
does not support the electrodes 406. The electrodes 406 are
supported on the major surface 408 of the test strip 400. Different
patterns of conductive material 402 can be used to specify
different assays (e.g., glucose, ketone bodies, etc.). For each
different assay, the pattern of conductive material 402 is disposed
in such a way that the electrical contacts IDENT1, IDENT2, and
IDENT3 of the test port 110 interact with the conductive material
in the pattern to identify the type of assay that will be performed
by the test strip 400, such as, for example, glucose, ketone
bodies, lactate. A device circuit 212, such as an ASIC (see FIG.
2), identifies the type of assay that will be performed by the test
strip 400 by determining the pattern of connection of the
conductive material 402 on the major surface 404 of the test strip
400.
[0049] When a strip (e.g., calibration strip, glucose test strip,
ketone bodies test strip, etc.) is inserted into test port 110 of
the analyte test instrument 100, the analyte test instrument 100
detects the presence of the strip and performs a procedure to
determine whether the strip is a calibration strip or a test strip
for determination of the concentration of an analyte. First, the
instrument software 220 polls the test port 110 to identify the
function of the strip that has been inserted, i.e. calibration
strip, test strip for determination of the concentration of an
analyte. In one embodiment, the instrument software 220 attempts to
communicate with the inserted strip by means of a protocol capable
of operating with a serial EE-squared interface, such as that
defined by the Dallas ROM protocol of Dallas Semiconductor, Dallas
Tex. Such an interface provides single-wire communication. If the
attempt to communicate is successful, the instrument software 220
proceeds to the ROM calibration procedure. If the attempt to
communicate is unsuccessful, the instrument software 220 puts the
analyte test instrument 100 into a brief wait mode (a predetermined
time period), e.g., three to five minutes. If the analyte test
instrument 100 fails to receive a signal indicating that a sample
has been received during the waiting period, the analyte test
instrument 100 shuts itself off automatically.
[0050] The receipt of a signal by microprocessor 216 indicates that
the user is performing an assay for determination of the
concentration of an analyte. Referring to FIG. 3A, when a test
strip 230 is inserted into the test port 110, the electrical
contacts 232 communicate with the analyte test instrument 100. When
a sample (not shown) is added to the reaction area 236, the sample
reacts with the reagents in the reaction area, thereby causing a
flow of electrons to produce an electrical response, such as a
change in current. The response is detectable by the analyte test
instrument 100. The analyte test instrument 100 converts the
detected signal into data corresponding to information relating to
the analyte and displays the information to the user.
[0051] FIG. 5 illustrates the ROM calibration procedure when a
calibration strip is introduced into the test port 110. When the
instrument software 220 identifies the calibration strip 240 (step
710), data from the ROM 250 is downloaded to the analyte test
instrument 100 (step 720). After the data from the ROM 250 has been
downloaded to the analyte test instrument 100, the display 130
displays the lot number downloaded from the calibration strip 240
(step 730), as an indication that the calibration is complete. This
data is stored in the memory 218 (step 740). The user can then
remove the calibration strip from the test port 110 (step 750). The
downloaded data remains in the memory 218 for use by the analyte
test instrument 110 until a new calibration procedure is performed
(step 760). In some embodiments, the analyte test instrument 100
can store more than one set of calibration data in the memory 218.
For example, an analyte test instrument 100 capable of performing
assays with a plurality of test strips 230 (e.g., glucose, ketone
bodies), can store a set of calibration data for each type of test
strip 230.
[0052] As described in U.S. Pat. No. 6,377,894, incorporated herein
by reference, the downloaded and stored data comprises parameters,
algorithms, operational procedures, and the like for controlling
the operation of the analyte test instrument 100. In a preferred
embodiment of this invention, the data comprise information that
instructs the analyte test instrument to perform an assay with a
test strip having two electrodes or with a test strip having three
electrodes. In another preferred embodiment, the data comprise
information that instructs the analyte test instrument 100 to begin
an assay in a mode where the circuitry anticipates a test strip
having two electrodes and then switch to a mode where the circuitry
is changed to accommodate a test strip having three electrodes.
Operation
[0053] FIG. 6 depicts a flow chart of a method of performing an
assay with the analyte test instrument of this invention. A
calibration strip 240 is inserted into the test port 110 and
information about types of assays (e.g., glucose, ketone bodies)
and the configuration of the test strip circuit 214 (i.e., two
electrodes or three electrodes) are downloaded and stored in the
memory 218 of the analyte test instrument 100 (step 800). The
calibration strip 240 is removed from the test port 110. A test
strip 230 is inserted into the test port 110 (step 810). The
microprocessor 216 of the analyte test instrument 100 determines
whether the strip inserted into the test port 110 is a test strip
230 or a calibration strip 240 by transmitting a digital signal
along a wire to the strip. If no signal is received from the strip,
the microprocessor 216 has determined that the strip is a test
strip 230. The microprocessor 216 then determines the pattern of
electrical contacts on the major surface of the test strip 230 that
does not support the electrodes (step 820). The aforementioned
pattern of electrical contacts provides a signal to the
microprocessor 216 indicating the assay that can be performed with
the test strip 230 that has been inserted into the test port 110,
such as, for example, a glucose assay, a ketone bodies assay. The
microprocessor 216 then sets the switches of the test strip circuit
214 to the mode for a test strip having two electrodes (step 830).
A sample is then introduced to the reaction area 236 of the test
strip 230. A voltage is applied, and after a brief period of time,
a small current can be detected (step 840). The current indicates
that a sample, which covers the electrodes, has been detected (step
850). When the current is detected, the microprocessor 216
instructs a switch (not shown) in the device circuit 212 to open,
thereby disconnecting the electrodes on the test strip from the
test strip circuit 214 for a specified period of time (step 860),
which period has been preset by the microprocessor 216. After the
specified period of time, the switch (not shown) in the device
circuit 212 is closed and the test strip circuit 214 remains in the
two-electrode mode if the test strip is one having two electrodes,
or the switches (not shown) in the test strip circuit 214 are set
for a test strip having three electrodes (step 870) if the test
strip is one having three electrodes. The appropriate electrode
mode is determined by the microprocessor 216. The appropriate level
of voltage is applied, and the current resulting from the
electrochemical reaction between the sample and the reagents on the
test strip is measured (step 880). The microprocessor 216 then
converts the current measured into the appropriate value of
concentration of analyte by means of parameters and algorithms that
had been previously supplied by the calibration strip 240 and
stored in the memory 218. The microprocessor 216 then instructs the
display 130 to show the value of the concentration of analyte (step
890). Assays for different types of analytes and assays employing
different types of test strips, i.e., test strips having two
electrodes and test strips having three electrodes, can be carried
out on the same analyte test instrument 100. If the characteristics
of test strip for a particular assay are changed, such as, for
example, a new assay for glucose is developed, the instructions for
the analyte test instrument can be changed merely by using a new
calibration strip; the analyte test instrument need not be
discarded.
[0054] FIG. 7A, FIG. 7B, and FIG. 8 illustrate a test strip circuit
214 that can be used to perform assays with two different types of
test strips--a test strip having two electrodes and a test strip
having three electrodes. FIG. 7A and FIG. 7B show a top view of a
test strip 900 having three electrodes, the test strip inserted in
the test port 110. The test strip 900 is shown without its
insulating coating, whereby a working electrode 902, a counter
electrode 904, and a reference electrode 906 are visible. The
electrical contacts 908 at the end 910 of the test strip 900 are
also visible. FIG. 8 shows a top view of a test strip 900a having
two electrodes, the test strip inserted in the test port 110. The
test strip 900a is shown without its insulating coating, whereby a
working electrode 912, a dual-purpose reference/counter electrode
914, and a trigger electrode 916 are visible. The electrical
contacts 918 at the end 920 of the test strip 900a are also
visible. FIG. 3A shows a test strip 230 having an insulating
coating 238 present. In FIG. 7A, the electrical contacts 908 at the
end 910 of the test strip 900 are shown inserted into the test port
110, where they make contact with electrical contacts SENS1, SENS2,
and SENS3. These electrical contacts are depicted in FIG. 2. The
electrical contacts SENS1, SENS2, SENS3 make electrical contact
with the active electrical components of the test strip circuit 214
through wires 922, 924, and 926, respectively. The wires 922 and
924 have switches 928 and 930, respectively, controlled by the
microprocessor 216, located between the electrical contacts (not
shown) of the test port 110 and the test strip circuit 214. The
switches 928 and 930 are used to connect or disconnect the
electrical contacts SENS1 and SENS3 from the test strip circuit
214. FIG. 7A also shows operational amplifiers 932 and 934;
resistors 940, 942, and 944; microprocessor-controlled switch 946;
two analog-to-digital (A/D) converters 950 and 952; and two
digital-to-analog (D/A) converters 954 and 956. The microprocessor
216 shown in FIG. 7A is part of the processing circuit 210. The
processing circuit is shown schematically in FIG. 2.
[0055] The test strip circuit 214 is first set in the two-electrode
mode by the microprocessor 216. FIG. 7A shows switch 946 set in the
two-electrode mode. The working electrode 902 is disconnected from
the test strip circuit 214 by means of a microprocessor-controlled
switch 928 in the wire 922. The D/A converter 956 receives a
digital voltage instruction from the microprocessor 216 and applies
an analog voltage, 400 mV, between the counter electrode 904 and
the reference electrode 906 by means of the operational amplifier
932. The microprocessor 216 continues to interrogate the A/D
converter 952. When a sufficient quantity of the sample is applied
to the test strip 900 to result in a fluid connection between the
counter electrode 904 and the reference electrode 906, a current
begins to flow between the two electrodes. When the current reaches
a threshold, e.g., 0.5 microamperes, the microprocessor 216 opens
the switch 930 in the wire 924 leading to the reference electrode
906 for a short period of time, e.g., from about 0 to about 10
seconds. The next instructions from the microprocessor 216 differ,
depending on whether the assay employs a test strip having two
electrodes or a test strip having three electrodes.
[0056] If the assay involves a test strip employing three
electrodes, the switch 946 is set at shown in FIG. 7B. The
microprocessor-controlled switches 928 and 930 in the wires 922 and
924, respectively, are closed. The D/A converter 954 receives a
digital voltage instruction from the microprocessor 216 and applies
an analog voltage, 200 mV, to the working electrode 902 by means of
the operational amplifier 934. The current originating at the
working electrode 902 as a result of the reaction of the sample
with the reagent is converted by the A/D converter 950 to a digital
signal that is received by the microprocessor 216. The
microprocessor 216 receives the digital signal from the A/D
converter 950 at a specific time or at specific times. The
microprocessor 216 can receive data from the A/D converter 950 at
more than one time window, and the data from the different time
windows can be used to perform error checks on the assay. Typical
time windows for the microprocessor 216 to receive data are 4 to 5
seconds and 8 to 10 seconds. The microprocessor 216 uses the
digital signal to calculate a concentration of analyte in the
sample by using calibration factors supplied by a calibration
strip. The concentration can then be displayed on the display 130
of the analyte test instrument 100.
[0057] If the assay employs a test strip having two electrodes, the
switch 946 remains in the position shown in FIG. 8. The test strip
circuit 214 is first set in the two-electrode mode by the
microprocessor 216. FIG. 8 shows the switch 946 set in the
two-electrode mode. The working electrode 912 is disconnected from
the test strip circuit 214 by means of the
microprocessor-controlled switch 928 in the wire 922. The D/A
converter 956 receives a digital voltage instruction from the
microprocessor 216 and applies an analog voltage, 400 mV, between
the trigger electrode 916 and the dual-purpose reference/counter
electrode 914 by means of the operational amplifier 932. The
microprocessor 216 continually interrogates the D/A converter 952.
When a sufficient quantity of sample is applied to the test strip
900a to result in a fluid connection between the fill trigger
electrode 916 and the dual-purpose reference/counter electrode 914,
a current begins to flow between the two electrodes. When the
current reaches a threshold, e.g., 0.5 microamperes, the
microprocessor 216 opens the switch 930 in the wire 924 leading to
the trigger electrode 916 for a short period of time, e.g., from
about 0 to about 10 seconds. Because the assay employs a test strip
having two electrodes, the switch 946 remains in the position shown
in FIG. 8. The microprocessor-controlled switch 928 in the wire 922
is closed. The D/A converter 954 receives a digital voltage
instruction from the microprocessor 216 and applies an analog
voltage, 200 mV, to the working electrode 912 by means of the
operational amplifier 934. The current originating from the working
electrode 912 resulting from the reaction of the sample with the
reagent is converted by the A/D converter 950 into a digital signal
that is received by the microprocessor 216. The microprocessor 216
receives the digital signal from the A/D converter 950 at a
specific time or at specific times. The microprocessor 216 can
receive data from the A/D converter 950 at more than one time
window, and the data from the different time windows can be used to
perform error checks on the assay. Typical time windows for the
microprocessor 216 to receive data are 4 to 5 seconds and 8 to 10
seconds. The microprocessor 216 uses the digital signal to
calculate a concentration of analyte in the sample by using
calibration factors supplied by a calibration strip. The
concentration can then be displayed on the display 130 of the
analyte test instrument 100.
[0058] FIG. 7A, FIG. 7B, and FIG. 8 demonstrate that the same test
strip circuit 214 can be used to analyze test strips having either
two electrodes or three electrodes. The analyte test instrument of
this invention is therefore more versatile than analyte test
instruments of the prior art. The analyte test instrument of this
invention can identify the type of test strip inserted into the
instrument (i.e., one having two electrodes or one having three
electrodes), and, by using stored calibration information, can
configure the analyte test instrument appropriately without relying
on input from the user. The analyte test instrument of this
invention is therefore easier for the user to switch from one
circuit to another than are analyte test instruments of the prior
art.
[0059] The test strip circuit of the analyte test instrument of
this invention and the method wherein a two-electrode mode is
employed at the beginning of the assay to detect when the test
strip is filled allows measurements to be made with much less
expensive operational amplifiers, thereby reducing the cost of the
analyte test instrument while providing performance characteristics
of expensive analyte test instruments.
[0060] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and spirit of this invention, and it should be understood
that this invention is not to be unduly limited to the illustrative
embodiments set forth herein.
* * * * *