ELECTROCHEMICAL-SENSOR DESIGN

• US 20040200720A1
• Filed: 05/21/2001
• Published: 10/14/2004
• Est. Priority Date: 08/02/1999
• Status: Active Grant

• Current Assignee: Ascensia Diabetes Care Holdings AG (PHC Holdings Corporation)
• Original Assignee: Bayer Corporation (Bayer AG)
• Inventors: Noell, J. Oakey, Huang, Dijia, Edelbrock, Andrew J., Musho, Matthew K.
• Granted Patent: US 6,841,052 B2
• Time in Patent Office: Days
• US Class Current: 204/403.01
• CPC Class Codes: C12Q 1/001 Enzyme electrodes
• CPC Class Codes: G01N 27/3274 Corrective measures, e.g. error detection, compensation for temperature or hematocrit, calibration coding of calibration information G01N33/48771

Abstract

Disclosed is an improved electrochemical sensor having a base bearing a working and counter electrode which provides a flow path for a fluid test sample. The working electrode has a reaction layer on its surface which contains an enzyme capable of reacting with an analyte to produce electrons which are received by the working electrode. The base is mated with a cover to form a capillary space into which the test fluid is drawn. The improvement involves configuring the working and counter electrodes so that a major portion of the counter electrode is located downstream on the flow path from the working electrode with the exception of a small sub-element of the counter electrode which is in electrical communication with the primary portion of the counter electrode and located upstream of the working electrode. This configuration provides the sensor with the capability of sending a greatly reduced electrical signal to the device'"'"'s detecting element in the event that the capillary space is incompletely filled with test fluid. This reduced signal can be manipulated to produce an error signal which affirmatively apprises the device'"'"'s user that such incomplete filling has occurred.

Claims

1-13. -13. (canceled)

14. A system for detecting the concentration of analyte in a fluid test sample which comprises an electrochemical sensor for detecting the concentration of analyte in a fluid test sample, the sensor comprising a base which provides a flow path for the fluid test sample having on its surface a counter electrode and a working electrode in electrical communication with a detector of electrical current, a reaction layer on the surface of at least the working electrode comprising an enzyme which reacts with the analyte to produce electrons that are transferred to the working electrode, and a cover which when mated with the base member forms a capillary space with an opening for the introduction of fluid test sample thereto which space contains the flow Path for the fluid test sample in which the counter and working electrodes are situated so that the major portion of the counter electrode is located downstream of the opening from the working electrode with a sub-element of the counter electrode being upstream of the working electrode so that when electrical communication between only the sub-element and working electrode takes Place there is insufficient flow of electrical current through the detector to constitute a valid test for the concentration of analyte in the fluid test sample and the detector is preprogrammed to emit an error signal in the event of such insufficient flow of electrical current,

wherein the sensor is in electrical connection with a meter which has been algorithmically programmed to a) make multiple current measurements at different time periods when a driving potential is applied between the electrodes, b) convert the multiple current measurements into error checking parameters and c) check the values of these parameters against their corresponding tolerance bands to determine if a short fill has occurred.

15. The system of claim 14 wherein the analyte is glucose and the system is programmed to apply a 0.4V potential for 10 seconds after the fluid test sample is applied, which is a first 10-second period, open the circuit so as to create OV potential for 10 seconds, which is a second 10-second period, apply a 0.4V potential for 10 seconds, which is a third 10-second period, and

A) make a current measurement at the end of the first 10 second period which is designated as I_b10, 5 seconds into the third 10 second period designated as I_r5 and at the end of the third 10 second period designated as I_r10,

B) determine the decay factor which describes the shape of the current time course by solving the equation:

$k=\frac{\ln <br><br>\left(I_{\mathrm{r5}}\right)-\ln <br><br>\left(I_{r<br><br>\text{\hspace{1em}<br><br>}<br><br>10}\right)}{\ln <br><br>\left(10\right)-\ln <br><br>\left(5\right)}$

and the Read-to-Burn ratio, (R/B) by solving the equation;

R/B=I_r10/I_b10

C) check the values of the decay factor and the Read-to-Burn ratio against their tolerance limits for k as;

Condition 1 (Decay factor checking);

$\mathrm{if}<br><br><br><br>k-\left(a_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1}+b_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1}<br><br>\text{\hspace{1em}<br><br>}·<br><br>\text{\hspace{1em}<br><br>}<br><br>G\right)<br><br>><br><br>w_k<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{is}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{true}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{when}<br><br>\text{\hspace{1em}<br><br>}<br><br>G\le <br><br>d_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1},\text{\hspace{1em}<br><br>}<br><br>\mathrm{or}$$\mathrm{if}<br><br><br><br>k-\left(a_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>2}+b_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>2}<br><br>\text{\hspace{1em}<br><br>}·<br><br>\text{\hspace{1em}<br><br>}<br><br>G\right)<br><br>><br><br>w_k<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{is}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{true}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{when}<br><br>\text{\hspace{1em}<br><br>}<br><br>d_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>1}<<br><br>G\le <br><br>d_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>2},\text{\hspace{1em}<br><br>}<br><br>\mathrm{or}$$\mathrm{if}<br><br><br><br>k-\left(a_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>3}+b_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>3}<br><br>\text{\hspace{1em}<br><br>}·<br><br>\text{\hspace{1em}<br><br>}<br><br>G\right)<br><br>><br><br>w_k<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{is}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{true}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{when}<br><br>\text{\hspace{1em}<br><br>}<br><br>G><br><br>d_{k<br><br>\text{\hspace{1em}<br><br>}<br><br>2}$

where a_k1, a_k2, a_k3, b_k1, b_k2, b_k3, W_k, d_k1, d_k2, and d_k3 are predetermined constants, G is the glucose measurement,

and for R/B as;

Condition 2 (R/B ratio checking);

if|R/B−

(a_c1+b_c1·

G)|>

w_c is true when G≦

d_c, or if|R/B−

(a_c2+b_c2·

G)|>

w_c is true when G>

d_c

where a_c1, a_c2, b_c1, b_c2, w_c, and d_c are predetermined constants, G is the glucose measurement, and

D) conclude that there has been a short fill if either Condition 1 or Condition 2 is true.