Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – Involving enzyme or micro-organism
Reexamination Certificate
1998-08-24
2001-06-26
Tung, T. (Department: 1743)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
Involving enzyme or micro-organism
C205S775000, C204S402000, C204S403060
Reexamination Certificate
active
06251260
ABSTRACT:
FIELD OF THE INVENTION
The invention is generally related to a method of determining a concentration of an analyte in a solution through measuring a potential, the potential varying about linearly with the concentration of the analyte. The method of the invention enables reproducible electrochemical determination of analyte concentration with electrodes having a variety of sizes, in cells having a variety of volumes, while resolving small changes in the concentration of the analyte.
BACKGROUND OF THE INVENTION
The concentration of glucose and other chemicals and biochemicals can be monitored electrochemically through potentiometry, amperometry or coulometry. (See , for example, Hall, E. A. H.,
Biosensors
, Prentice Hall, N.J., 1991, Chapters 8 and 9). While amperometry requires knowledge of the area of the electrode and coulometry requires knowledge of the liquid volume analyzed, potentiometry does not require such knowledge. In high volume manufacturing, control of electrode dimensions or microcell volumes is of essence, respectively in amperometric or coulometric biosensors, but not in potentiometric ones. The disadvantage of potentiometric devices has been that their output scaled with the logarithm of the concentration of the analyte rather than with its concentration. Consequently, the penalty in potentiometry has been the inability to resolve small changes in concentrations.
Potentiometric assays, unlike amperometric or coulometric ones, do not require accurate definition and knowledge of the area of the measuring electrode or microcell volume. Large scale manufacturing of devices for potentiometric assay, for example of strips for single-use potentiometric self-monitoring of blood glucose concentrations by diabetic patients, would therefore not require the tight control of size, microroughness, or microcell volume that is required for large scale manufacturing of available amperometric, chronoamperometric or chronocoulometric strips. However, the potential increases or decreases usually approximately linearly with the logarithm of the analyte concentration, while the current in amperometry and the charge in coulometry increases usually approximately linearly with the analyte concentration. For this reason, changes in glucose concentration were previously better resolved by amperometry or coulometry than by potentiometry. Also, in large arrays of sensors, such as those produced, for example, through combinatorial processes to have large numbers of different elements, it is necessary to compare the magnitude of signals from different sensing elements. Better resolution of differences between elements of an array, in which not all elements are necessarily of the same size, is enabled through potentiometry, if the potentiometrically derived signal scales about linearly with the concentration of the analyte rather than with the logarithm of its concentration.
SUMMARY OF THE INVENTION
A method has now been developed that allows the realization of the advantages of both the electrode area or cell volume independence of potentiometry, and the linear, rather than logarithmic, scaling of the signal with analyte concentration. These advantages are simultaneously realized when the electrode is coated with a resistive, but nevertheless electron-conducting, film. The analyte is electrooxidized or electroreduced on or in this film.
In one example of a glucose sensor, a working electrode includes a film that has a redox polymer that electrically connects (“wires”) reaction centers of an enzyme, such as glucose oxidase, catalyzing the electrooxidation of glucose at the electrode. After a potential pulse is applied to the “wired” enzyme electrode so that the electrode-bound redox centers are electrooxidized, the floating electrode potential decays to a value that varies linearly with the concentration of glucose. It is believed that the dependence of this potential on analyte concentration is linear when the potential is dominated by the ohmic resistance of the redox polymer film, not by the overpotential of electron transfer from the electrode to the film.
The instant invention thus provides a potentiometric analyte sensor and method for determination of an analyte in a sample using a potentiometric assay system, where the potential varies approximately linearly with the concentration of the analyte.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.
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Heller Adam
Yarnitzky Chaim
Merchant & Gould P.C.
Noguerola Alex
TheraSense Inc.
Tung T.
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