Method and apparatus for amperometric diagnostic analysis

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.

We claim: 
     
       1. A method of measuring the amount of a selected compound in body fluids comprising, a) providing a measuring cell having at least a first and second electrode and said cell containing an oxidant and a buffer,   b) placing a sample of fluid to be tested in said cell,   c) reconstituting said oxidant and buffer with said sample fluid to generate a predetermined reaction,   d) allowing said reaction to proceed substantially to completion,   e) applying a potential across said electrodes and sample, and   f) measuring the resulting Cottrell current to determine the concentration of said selected compound present in said sample.   
     
     
       2. A method as set forth in claim 1, wherein the compound is selected from the group consisting of glucose, cholesterol, TSH, T4, hormones, antiarrhythmics, antiepileptics and nontherapeutic drugs. 
     
     
       3. A method as set forth in claim 1, wherein the oxidant is a material selected from the group consisting of benzoquinone, ferricyanide, ferricinium, .Iadd.orthophenanthroline .Iaddend.and Cobalt (III) dipyridyl. 
     
     
       4. The method as set forth in claim 1 including providing as said first electrode a working electrode and as said second electrode a reference electrode.   
     
     
       5. The method of claim 1 including also providing in said cell . .and.!. .Iadd.an .Iaddend.enzyme as a catalyst and said enzyme is an oxidoreductase. 
     
     
       6. The method of claim 1 including selecting said buffer from the group consisting of phosphate, TRIS, MOPS, MES, HEPES, Tricine, Bicine, ACES, CAPS and TAPS. . .7. A method for measuring the amount of glucose in blood, comprising a) providing a measuring cell having at least a first and second electrode and said cell containing an oxidant, a buffer and an enzyme,   b) placing a blood sample to be tested in said cell,   c) reconstituting said oxidant, buffer and enzyme with said blood sample to generate a predetermined reaction,   d) essentially immediately applying a potential across said electrodes and blood sample, and   e) measuring the resultant Cottrell current when the reaction has proceeded to completion to determine the concentration of said glucose present in   
     
     
        blood sample..!.. .8.  The method of claim 7 including selecting said oxidant from the group consisting of benzoquinone, ferricyanide, ferricinium, Cobalt (III) orthophenantroline, and Cobalt (III) dipyridyl..!.. .9. The method of claim 7 including providing as said first electrode a working electrode and said second electrode a reference electrode..!.. .10. The method of claim 7 including adding as said enzyme, 
     
     
        glucose oxydase..!.11. The method of claim 1 wherein .Iadd.the sample of fluid is blood and .Iaddend.in step b) said placing of the blood sample to be tested in the cell generates a current and initiates a timing sequence, and wherein the reaction of step d) is allowed to proceed with an open circuit between said first and second . .electrode.!. .Iadd.electrodes.Iaddend.. .Iadd.12. A method of measuring the amount of an analyte in a blood sample, comprising: a) adding the blood sample to an electrochemical cell that includes an electron transfer agent that will react in a reaction involving the analyte, thereby forming a detectable species;   b) incubating the reaction involving analyte and electron transfer agent in an open circuit until the reaction has substantially completed;   c) applying a sufficient potential difference between the electrodes of the electrochemical cell, after the incubation step, to readily transfer at least one electron between the detectable species and one of the electrodes, thereby resulting in a Cottrell current;   d) measuring the Cottrell current; and   e) correlating the measured Cottrell current to the amount of analyte in   
     
     
        the blood sample..Iaddend..Iadd.13.  The method of claim 12, wherein adding the blood sample to the electrochemical cell causes a sudden charging current, which automatically initiates incubation step b) performed under open circuit..Iaddend..Iadd.14. The method of claim 13, wherein the Cottrell current is measured at a preset time following the incubation step..Iaddend..Iadd.15. The method of claim 12, wherein the electrochemical cell further includes a catalyst in sufficient amount to catalyze the reaction involving the analyte and the electron transfer agent..Iaddend..Iadd.16. The method of claim 15, wherein the catalyst is an enzyme..Iaddend..Iadd.17. The method of claim 16, wherein the analyte is glucose and the enzyme is glucose oxidase..Iaddend..Iadd.18. The method of claim 12, wherein the electron transfer agent is included in a reagent layer that is coated directly onto the electrochemical cell or is incorporated into a supporting matrix that is placed into the electrochemical cell..Iaddend..Iadd.19. The method of claim 18, wherein the supporting matrix is filter paper, membrane filter, woven fabric, or nonwoven fabric..Iaddend..Iadd.20. The method of claim 18, wherein the reagent layer further includes a binder..Iaddend..Iadd.21. The method of claim 20, wherein the binder is gelatin, carrageenan, methylcellulose, polyvinyl alcohol, or polyvinylpyrrolidone..Iaddend..Iadd.22. The method of claim 21, wherein a dispersing, spreading, or wicking layer overlays the reagent layer..Iaddend..Iadd.23. The method of claim 18, wherein adding the blood sample to the electrochemical cell causes a sudden charging current, which automatically initiates incubation step b) performed under open circuit..Iaddend..Iadd.24. The method of claim 23, wherein the Cottrell current is measured at a preset time following the incubation step..Iaddend..Iadd.25. The method of claim 24, wherein the reagent layer further includes an enzyme catalyst in sufficient amount to catalyze the reaction involving the analyte and the electron transfer 
     
     
        agent..Iaddend..Iadd.26.  The method of claim 25, wherein the analyte is glucose in a concentration from about 1 milligram glucose per deciliter of blood sample to about 1000 milligrams glucose per deciliter of blood sample, and the fluid sample is blood..Iaddend..Iadd.27. The method of claim 26, wherein the electron transfer agent is ferricyanide, ferricinium, cobalt (III) orthophenanthroline, cobalt (III) dipyridyl, or benzoquinone..Iaddend..Iadd.28. The method of claim 12, wherein the analyte is glucose, TSH, T 4 , a hormone, a cardiac glycoside, an antiarrhythmic, an antiepileptic, an antibiotic, cholesterol, or a non-therapeutic drug..Iaddend..Iadd.29. The method of claim 25, wherein the analyte is glucose in a concentration from about 1 milligram glucose per deciliter of blood sample to about 1000 milligrams glucose per deciliter of blood sample, the incubation period is from about 15 seconds to about 160 seconds, and current measurements are made in the range from about 2 seconds to about 30 seconds following the incubation step..Iaddend..Iadd.30. A method of measuring the amount of an analyte in a blood sample, comprising: a) adding the blood sample to an electrochemical cell that includes an electron transfer agent,   a first catalyst in sufficient amount to catalyze a first reaction involving the analyte, and   a second catalyst in sufficient amount to catalyze a second reaction involving a product of the first reaction and the electron transfer agent, thereby forming a detectable species;     b) incubating the first and second reactions in an open circuit until the reactions have substantially completed;   c) applying a sufficient potential difference between electrodes of the electrochemical cell, after the incubation step, to readily transfer at least one electron between the detectable species and one of the electrodes, thereby resulting in a Cottrell current;   d) measuring the Cottrell current; and   e) correlating the measured Cottrell current to the amount of analyte in   
     
     
        the blood sample..Iaddend..Iadd.31.  The method of claim 30, wherein adding the blood sample to the electrochemical cell causes a sudden charging current, which automatically initiates incubation step b) performed under open circuit..Iaddend..Iadd.32. The method of claim 31, wherein the Cottrell current is measured at a preset time following the incubation step..Iaddend..Iadd.33. A method of measuring the amount of cholesterol in a blood sample, comprising: a) adding the blood sample to an electrochemical cell that includes an electron transfer agent,   cholesterol esterase in sufficient amount to catalyze the hydrolysis of cholesterol esters in the blood sample, thereby forming cholesterol,   cholesterol oxidase in sufficient amount to catalyze a reaction involving cholesterol and the electron transfer agent, thereby forming a detectable species;     b) incubating the reactions of step a) in an open circuit until those reactions have substantially completed;   c) applying a sufficient potential difference between electrodes of the electrochemical cell, after the incubation step, to readily transfer at least one electron between the detectable species and one of the electrodes, thereby resulting in a Cottrell current;   d) measuring the Cottrell current; and   e) correlating the measured Cottrell current to the amount of cholesterol in the blood sample..Iaddend..Iadd.34. The method of claim 33, wherein adding the blood sample to the electrochemical cell causes a sudden charging current, which automatically initiates incubation step b) performed under open circuit..Iaddend..Iadd.35. The method of claim 34, wherein the Cottrell current is measured at a preset time following the incubation step..Iaddend..Iadd.36. The method of claim 35, wherein the electron transfer agent is ferricyanide or   
     
     
        benzoquinone..Iaddend..Iadd.     A method of measuring the amount of an analyte in a blood sample, comprising: a) adding the blood sample to an electrochemical cell that includes first and second electron transfer agents,   a first catalyst in sufficient amount to catalyze a first reaction involving the analyte,   a second catalyst in sufficient amount to catalyze a second reaction involving a product of the first reaction and the first electron transfer agent, thereby forming an intermediate species that reacts with the second electron transfer agent, thereby forming a detectable species;     b) incubating the reactions of step a) in an open circuit until those reactions have substantially completed;   c) applying a sufficient potential difference between electrodes of the electrochemical cell, after the incubation step, to readily transfer at least one electron between the detectable species and one of the electrodes, thereby resulting in a Cottrell current;   d) measuring the Cottrell current; and   e) correlating the measured Cottrell current to the amount of analyte in the blood sample..Iaddend..Iadd.38. A method of measuring the amount of cholesterol in a blood sample, comprising:   a) adding the blood sample to an electrochemical cell that includes first and second electron transfer agents,   cholesterol esterase in sufficient amount to catalyze the hydrolysis of cholesterol esters in the blood sample, thereby forming cholesterol,   cholesterol oxidase in sufficient amount to catalyze a reaction involving cholesterol and the first electron transfer agent, thereby forming an intermediate species that reacts with the second electron transfer agent, thereby forming a detectable species;     b) incubating the reactions of step a) in an open circuit until those reactions have substantially completed;   c) applying a sufficient potential difference between the electrodes of the electrochemical cell, after the incubation step, to readily transfer at least one electron between the detectable species and one of the electrodes, thereby resulting in a Cottrell current;   d) measuring the Cottrell current; and   e) correlating the measured Cottrell current to the amount of cholesterol   
     
     
        in the blood sample..Iaddend..Iadd.39.  The method of claim 38, wherein adding the blood sample to the electrochemical cell causes a sudden charging current, which automatically initiates incubation step b) performed under open circuit..Iaddend..Iadd.40. The method of claim 39, wherein the Cottrell current is measured at a preset time following the incubation step..Iaddend..Iadd.41. The method of claim 40, wherein the first electron transfer agent is benzoquinone, phenazine ethosulfate, phenazine methosulfate, tetramethylbenzidine, a derivative of benzoquinone, naphthoquinone, a derivative of naphthoquinone, anthraquinone, a derivative of anthraquinone, catechol, phenylenediamine, tetramethylphenylenediamine, or a derivative of phenylenediamine..Iaddend..Iadd.42. The method of claim 41, wherein the 
     
     
        second electron transfer agent is ferricyanide..Iaddend..Iadd.43.  A method for measuring the amount of a selected compound in a blood sample, comprising: providing a measuring cell having at least first and second electrodes for contact with the blood sample introduced into the cell,   applying a potential to the electrodes to detect the presence of the blood sample in the cell,   placing the blood sample into the cell,   removing the potential to the electrodes after the blood sample is detected in the cell,   selectively oxidizing the compound in the blood sample with an oxidized electron acceptor to produce an oxidized form of the selected compound and a reduced electron acceptor, and   re-applying a potential across the cell electrodes after the selective oxidation of the compound in the blood sample has substantially completed and measuring the resulting Cottrell current, said current being proportional to the concentration of the reduced electron acceptor and the selected compound in the blood sample..Iaddend..Iadd.44. The method of claim 43, wherein placing the fluid sample into the measuring cell causes a sudden charging current, which automatically initiates removal of the potential from the electrodes and performance of the selective oxidation of the selected compound under open circuit..Iaddend..Iadd.45. The method of claim 44, wherein the Cottrell current is measured at the preset time after re-application of a potential across the measuring cell electrodes..Iaddend..Iadd.46. The method of claim 47, wherein placing the volume of blood into the measuring cell causes a sudden charging current, which automatically initiates removal of the potential across the electrodes and performance of the oxidation of glucose in the blood under   
     
     
        open circuit..Iaddend..Iadd.47.  A method for measuring the amount of glucose in blood, comprising: providing a measuring cell with at least first and second electrodes for contact with blood introduced into the cell,   applying a potential across the electrodes,   placing a volume of blood into the cell,   removing the potential across the electrodes after the volume of blood is placed into the measuring cell,   oxidizing the glucose in the blood with an oxidized electron acceptor in the presence of glucose oxidase to produce gluconic acid and a reduced electron acceptor,   re-applying a potential across the measuring cell electrodes after the oxidation of glucose has substantially completed, and   measuring the Cottrell current through the cell, the Cottrell current being proportional to the glucose concentration in the blood..Iaddend..Iadd.48. The method of claim 46, wherein the Cottrell current is measured at a preset time after re-application of a potential across the measuring cell electrodes..Iaddend.