Biosensing instrument and method

• US 5,243,516 A
• Filed: 12/15/1989
• Issued: 09/07/1993
• Est. Priority Date: 12/15/1989
• Status: Expired due to Term

• Current Assignee: Roche Diabetes Care Inc. (Roche Holding AG)
• Original Assignee: Boehringer Mannheim Corporation
• Inventors: White, Bradley E.
• Primary Examiner(s): Envall, Jr., Roy N.
• Assistant Examiner(s): Huntley, David
• Application Number:
  US07/451,309
• Time in Patent Office: 1,362 Days
• Field of Search: 364/413.07, 364/413.11, 204/401, 204/403, 204/406, 435/817
• US Class Current: 435/287.2
• CPC Class Codes: G01N 27/3273 Devices therefor, e.g. test element readers, circuitry details not specific to biochemical electrodes G01N33/4875

Abstract

A biosensing system is described which determines whether a measured current is varying in accordance with a predetermined Cottrell current relationship. The system includes a test cell with at least a pair of electrodes which extend into a reaction zone, which reaction zone includes analyte reactants. An analog signal detector, in combination with a microprocessor, take plurality of current measurements between the electrodes over a plurality of succeeding measurement times, after a sample is placed in contact with the analyte reactants in the reaction zone. The microprocessor also stores a plurality of succeeding cpmparison constants which are derived by taking the inverse ratio of the square root of a measurement time divided by the square root of a subsequent measurement time. The microprocessor selects a pair of succeeding measurement times; derives a ratio of the currents measured at those times; and then compares the ratio of those currents with the comparison constant previously derived for the pair of succeeding measurement times. If the comparison indicates that the measured current ratio is dissimilar from the comparison constant, an indication is developed that the current between the electrodes is not varying in accordance with the Cottrell relationship. The plurality of current measurements are also used to calculate total charge transferred, Q. Q can then be used as a second means of calculating the final result.

Claims

1. A biosensor system for determining whether a current through a reaction zone is varying in accordance with a predetermined Cottrell current relationship, the combination comprising:

a test cell including electrode means and a reaction zone with analyte reactant;

means for obtaining a plurality of readings of current in said reaction zone over a plurality of measurement times, after a sample containing an analyte is placed in said reaction zone;

means for storing at least a comparison constant for a pair of succeeding measurement times, said comparison constant evidencing the inverse ratio of the square root of a measurement time divided by the square root of a subsequent measurement time;

means for deriving a ratio of the current readings obtained at said pair of succeeding measurement times; and

means for comparing said ratio of said current readings and said comparison constant for said pair of succeeding measurement times to determine if they are similar and if not, reporting an error condition.

2. The system as defined in claim 1 wherein:

said storing means includes a plurality of comparison constants for a plurality of succeeding measurement times; and

said deriving means derives ratios of current readings taken at said succeeding measurement times, and said comparison means compares said ratios with corresponding comparison constants, whereby said system determines if said current readings are following said Cottrell current relationship.

3. The system as defined in claim 2 wherein said test cell includes two electrodes which extend into a reaction zone, said electrodes covered by an analyte reactant containing layer.

4. In a system for measuring a current i passing through a reaction zone of a test cell, which current, in dependence upon the concentration of an analyte in the reaction zone, changes to follow one of a family of curves whose shape is defined by the Cottrell equation, a method for determining that said current is changing in accordance with the Cottrell equation, comprising the steps of:

(a) measuring said current i at a plurality of measurement times t_n, t_n+1, t_n+2 . . . to derive current values i_n, i_n+1, i_n+2 . . . ;

(b) calculating at least the value of the ratio of ##EQU5## to obtain a comparison constant;

(c) calculating the value of the ratio of ##EQU6## (d) comparing the comparison constant calculated in step b and with the ratio calculated in step c; and

(e) if said comparison indicates a dissimilarity, providing a signal indicating that said measured current in said test cell is not changing in accordance with said Cottrell equation.

5. The method as defined in claim 4 wherein the ratio defined in step b is calculated for a plurality measurement times to obtain a plurality of comparison constants.

6. The method as defined in claim 5 wherein a ratio, as defined in step c, is calculated for currents measured at each of the measurement times which are used to derive the comparison constants of claim 5.

7. The method of claim 6 wherein step d compares the comparison constants with ratios derived in step c for corresponding measurement times and step e provides a signal if any of said comparisons indicate a dissimilarity.

8. The method of claim 7 wherein said comparison constants obtained by step b are precalculated and stored.