Method and apparatus for amperometric diagnostic analysis

• US 6,413,411 B1
• Filed: 10/26/2000
• Issued: 07/02/2002
• Est. Priority Date: 02/09/1995
• Status: Expired due to Term

• Current Assignee: Decision IT Corp.
• Original Assignee: Tall Oak Ventures Co.
• Inventors: Talbott, Jonathan L., Jordan, Joseph, Pottgen, Paul A., Szuminsky, Neil J.
• Primary Examiner(s): Tung, T.
• Assistant Examiner(s): NOGUEROLA, ALEXANDER STEPHAN
• Application Number:
  US09/696,253
• Time in Patent Office: 614 Days
• Field of Search: 205/775, 205/777.5
• US Class Current: 205/777.5
• CPC Class Codes: G01N 27/3273 Devices therefor, e.g. test element readers, circuitry details not specific to biochemical electrodes G01N33/4875
• CPC Class Codes: Y10S 435/817 Enzyme or microbe electrode

Abstract

The present invention relates to a novel method and apparatus for the amperometric determination of an analyte, and in particular, to an apparatus for amperometric analysis utilizing a novel disposable electroanalytical cell for the quantitative determination of biologically important compounds from body fluids.

Claims

1. A method for measuring compounds in a sample fluid in a device including a housing having an access opening therethrough, a sample cell receivable into the access opening of the housing, the sample cell being composed of a first electrode which acts as a working electrode, a second electrode which acts to fix the system potential and provide opposing current flow with respect to the first electrode, the second electrode being made of the same electrically conducting material as the first electrode, and being operatively associated with the first electrode, the ratio of the surface area of the second electrode to the surface area of the first electrode being 1:

1 or less, and at least one non-conducting layer member having an opening therethrough, the at least one non-conducting layer member being disposed in contact with at least one of the first and second electrodes and being sealed against at least one of the first and second electrodes to form a known electrode area within the opening such that the opening forms a well to receive the sample fluid and to allow a user of the apparatus to place the sample fluid in the known electrode area in contact with the first electrode and the second electrode, comprising;

a) applying an electrical potential to both the first electrode and said second electrode;

b) creating an electrical circuit between the first electrode and the second electrode through the sample fluid;

c) measuring a first Cottrell current reading through the sample fluid at a first predetermined time after the electrical potential is applied and obtaining at least one additional Cottrell current reading through the sample fluid, the at least one additional Cottrell current reading occurring at a second predetermined time following the first predetermined time;

d) converting the first Cottrell current reading into a first analyte concentration measurement using a calibration slope and an intercept specific for the first Cottrell current measurement, converting the at least one additional Cottrell current reading into an additional analyte concentration using a calibration slope and an intercept specific for the at least one additional Cottrell current measurement, and comparing the first analyte concentration measurement with the at least one additional concentration measurement to confirm that they are within a prescribed percentage of each other; and

e) visually displaying the results of the analyte concentration measurements.

2. The method of claim 1, further comprising:

initiating an electrical potential upon insertion of the sample fluid to detect the presence of the sample fluid, signaling to commence a reaction timing sequence when the presence of the sample fluid is detected, and removing the potential during the reaction timing sequence.

3. The method of claim 1, wherein the first and second electrodes are spaced apart by a distance of at least about 0.1 mm and at most about 1 cm.

4. A method for obtaining measurements of an analyte contained in a sample in order to determine the concentration of analyte in the sample, in a device including a first electrical insulator, a pair of electrodes including working and counter electrodes, the working and counter electrodes being made of the same electrically conducting materials and being supported on the first electrical insulator, a second electrical insulator, overlaying the first electrical insulator and the working and counter electrodes and including a cutout portion that exposes surface areas of the working and counter electrodes, a reagent, substantially covering the exposed electrode surfaces in the cutout portion and including the oxidized form of a redox mediator, and an enzyme, the oxidized form of the redox mediator being capable of receiving at least one electron from a reaction involving enzyme, analyte, and the oxidized form of the redox mediator and being in sufficient amount to insure that current produced by diffusion limited electrooxidation as a result of the reaction is limited by the oxidation of the reduced form of the redox mediator at the working electrode surface, the enzyme being present in sufficient amount to catalyze the reaction involving the enzyme, analyte, and the oxidized form of the redox mediator, comprising:

(a) measuring a first Cottrell current attributable to the diffusion limited electrooxidation at a first predetermined time;

(b) measuring at least one second Cottrell current attributable to the diffusion limited electrooxidation at one or more subsequent predetermined times;

(c) converting the first Cottrell current into a first analyte concentration measurement using a calibration slope and an intercept specific for the first Cottrell current measurement;

(d) converting the at least one second Cottrell current reading into an additional analyte concentration using a calibration slope and an intercept specific for the at least one second Cottrell current measurement; and

(e) comparing the first analyte concentration measurement with the at least one additional concentration measurement to confirm that they are within a prescribed percentage of each other.

5. The method of claim 4, further comprising an initial step of incubating the reaction in an open circuit for a predetermined time.

6. The method of claim 4, wherein the initial step of incubating is initiated by adding the sample to the electrochemical cell.

7. A method for obtaining measurements of analytes contained in a sample in order to determine the concentration of analyte in the sample, in a system including reagents incorporated into a sample receiving portion of an electrochemical device that measures the analytes and that has a pair of electrodes including working and counter electrodes, the working and counter electrodes being made of the same electrically conducting materials, the ratio of the surface area of the counter electrode to the surface area of the working electrode being 1:

1 or less, the reagents including the oxidized form of a redox mediator, an enzyme, and a buffer, the oxidized form of the redox mediator being capable of receiving at least one electron from a reaction involving enzyme, analyte, and the oxidized form of the redox mediator and being present in sufficient amount to insure that current produced by diffusion limited electrooxidation as a result of the reaction following application of a potential to the working and counter electrodes is limited by the oxidation of the reduced form of the redox mediator at the working electrode surface, the enzyme being present in sufficient amount to catalyze the reaction involving the enzyme, analyte, and the oxidized form of the redox mediator, and the buffer having a higher oxidation potential than the reduced form of the redox mediator and being present in sufficient amount to provide and maintain a pH at which the enzyme catalyzes the reaction involving the enzyme, analyte, and the oxidized form of the redox mediator, comprising;

(a) measuring a first Cottrell current attributable to the diffusion limited electrooxidation at a first predetermined time;

(b) measuring at least one second Cottrell current attributable to the diffusion limited electrooxidation at one or more subsequent predetermined times;

(c) converting the first Cottrell current into a first analyte concentration measurement using a calibration slope and an intercept specific for the at least one second Cottrell current measurement; and

(d) comparing the first analyte concentration measurement with the at least one additional concentration measurement to confirm that they are within a prescribed percentage of each other.

8. A method for obtaining measurements of analytes contained in a sample in order to determine the concentration of analyte in the sample, in a system including reagents incorporated into a sample receiving portion of an electrochemical device that measures an analyte and that has a pair of electrodes including working and counter electrodes, the working and counter electrodes being made of the same electrically conducting materials, the ratio of the surface area of the counter electrode to the surface area of the working electrode being 1:

1 or less, the reagents including the reduced form of a redox mediator, an enzyme, and a buffer, the reduced form of the redox mediator being capable of donating at least one electron from a reaction involving enzyme, analyte, and the reduced form of the redox mediator and being present in sufficient amount to insure that current produced by diffusion limited electroreduction as a result of the reaction following application of a potential to the working and counter electrodes is limited by the reduction of the oxidized form of the redox mediator at the working electrode surface, the enzyme being present in sufficient amount to catalyze the reaction involving the enzyme, analyte, and the reduced form of the redox mediator, and the buffer having a lower reduction potential than the oxidized form of the redox mediator and being present in sufficient amount to provide and maintain a pH at which the enzyme catalyzes the reaction involving the enzyme, analyte, and the reduced form of the redox mediator, comprising;

(a) measuring a first Cottrell current attributable to the diffusion limited electroreduction at a first predetermined time;

(b) measuring at least one second Cottrell current attributable to the diffusion limited electroreduction at one or more subsequent predetermined times;

(c) converting the first Cottrell current into a first analyte concentration measurement using a calibration slope and an intercept specific for the first Cottrell current measurement;

(d) converting the at least one second Cottrell current reading into an additional analyte concentration using a calibration slope and an intercept specific for the at least one second Cottrell current measurement; and

(e) comparing the first analyte concentration measurement with the at least one additional concentration measurement to confirm that they are within a prescribed percentage of each other.

9. The method of claim 8, further comprising an initial step of incubating the reaction in an open circuit for a predetermined time.

10. The method of claim 9, wherein the initial step of incubating is initiated by adding the sample to the electrochemical cell.