Small volume in vitro analyte sensor and methods of making

• US 8,372,261 B2
• Filed: 09/29/2009
• Issued: 02/12/2013
• Est. Priority Date: 10/08/1998
• Status: Expired due to Fees

• Current Assignee: Abbott Diabetes Care Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Abbott Diabetes Care Incorporated (Abbott Laboratories Incorporated)
• Inventors: Feldman, Benjamin J., Heller, Adam, Heller, Ephraim, Mao, Fei, Vivolo, Joseph A., Funderburk, Jeffery V., Colman, Fredric C., Krishnan, Rajesh
• Primary Examiner(s): Noguerola, Alex
• Application Number:
  US12/569,020
• Publication Number:
  US 20100015326A1
• Time in Patent Office: 1,232 Days
• Field of Search: 20440301-40315, 205/777.5, 205/778, 205/792
• US Class Current: 205/777.5
• CPC Class Codes: C12Q 1/001 Enzyme electrodes
• CPC Class Codes: C12Q 1/006 for glucose
• CPC Class Codes: C12Q 1/32 involving dehydrogenase
• CPC Class Codes: G01N 27/3271 Amperometric enzyme electrodes for analytes in body fluids, e.g. glucose in blood amperometry per se G01N27/49; aspects concerning the enzyme reagent C12Q1/001
• CPC Class Codes: G01N 27/3272 Test elements therefor, i.e. disposable laminated substrates with electrodes, reagent and channels optical biosensors G01N33/52
• CPC Class Codes: G01N 27/3274 Corrective measures, e.g. error detection, compensation for temperature or hematocrit, calibration coding of calibration information G01N33/48771
• CPC Class Codes: Y10T 156/1052 with cutting, punching, tearing or severing
• CPC Class Codes: Y10T 29/49002 Electrical device making
• CPC Class Codes: Y10T 29/49004 including measuring or testing of device or component part
• CPC Class Codes: Y10T 29/49007 Indicating transducer
• CPC Class Codes: Y10T 29/49126 Assembling bases
• CPC Class Codes: Y10T 29/49128 Assembling formed circuit to base
• CPC Class Codes: Y10T 29/4913 Assembling to base an electrical component, e.g., capacitor, etc.
• CPC Class Codes: Y10T 29/49147 Assembling terminal to base
• CPC Class Codes: Y10T 29/49155 Manufacturing circuit on or in base
• CPC Class Codes: Y10T 29/49204 Contact or terminal manufacturing
• CPC Class Codes: Y10T 29/49208 by assembling plural parts
• CPC Class Codes: Y10T 29/4921 with bonding
• CPC Class Codes: Y10T 29/49794 Dividing on common outline

Abstract

A sensor utilizing a non-leachable or diffusible redox mediator is described. The sensor includes a sample chamber to hold a sample in electrolytic contact with a working electrode, and in at least some instances, the sensor also contains a non-leachable or a diffusible second electron transfer agent. The sensor and/or the methods used produce a sensor signal in response to the analyte that can be distinguished from a background signal caused by the mediator. The invention can be used to determine the concentration of a biomolecule, such as glucose or lactate, in a biological fluid, such as blood or serum, using techniques such as coulometry, amperometry, and potentiometry. An enzyme capable of catalyzing the electrooxidation or electroreduction of the biomolecule is typically provided as a second electron transfer agent.

Claims

1. A system for determining the concentration of an analyte in a sample fluid, the system comprising:

(a) a sensor comprising;

a first substrate having a proximal end and a distal end, the distal end being configured and arranged for insertion into a sensor reader;

a second substrate disposed over the first substrate;

a spacer disposed between the first and second substrates and defining a first aperture along the first side edge of the sensor, a second aperture along the second side edge of the sensor, and a sample chamber extending from the first aperture to the second aperture, wherein the sample chamber is sized to contain a volume of no more than about 1 μ

L of the sample;

a working electrode and a counter electrode disposed in the sample chamber, wherein the working electrode and the counter electrode are separated by a closest distance in a range of from 200 to 1000 μ

m; and

an analyte-responsive enzyme and a redox mediator disposed in the sample chamber;

(b) a sensor reader configured to;

apply a first potential and a second potential to determine fill of the sample chamber;

apply a third potential to electrolyze the analyte, thereby generating an analyte signal; and

determine the concentration of the analyte using the analyte signal.

2. The system of claim 1, wherein the sensor comprises an indicator electrode disposed in the sensor to indicate when the sample chamber contains a sample.

3. The system of claim 2, wherein the indicator electrode is also a working electrode or a counter electrode.

4. The system of claim 2, further comprising a visual or auditory sign, coupled to the indicator electrode, that activates when the indicator electrode indicates that the sample chamber contains sample.

5. The system of claim 2, wherein the indicator electrode is disposed in facing relationship to one of the working electrode and the counter electrode.

6. The system of claim 1, wherein the sensor comprises at least two indicator electrodes disposed in the sensor, wherein a first indicator electrode indicates when the sample chamber is beginning to fill with sample, and a second indicator electrode indicates when the sample chamber is substantially filled with sample.

7. The system of claim 2, wherein the sensor comprises at least two indicator electrodes disposed in the sensor, and wherein either the working electrode or the counter electrode is disposed between the at least two indicator electrodes.

8. The system of claim 1, wherein at least a portion of the working electrode is within an effective distance of no more than 200 μ

m of a portion of the counter electrode.

9. The system of claim 1, wherein the sensor is configured and arranged so that the mediator oxidizes the analyte and the half-wave potential of the redox mediator, as measured by cyclic voltammetry in 0.1 M NaCl at pH 7, is no more than about +100 millivolts relative to the potential of the counter/reference electrode.

10. The system of claim 1, wherein the sensor is configured and arranged so that the mediator oxidizes the analyte and the half-wave potential of the redox mediator, as measured by cyclic voltammetry in 0.1 M NaCl at pH 7, is about the same as the potential of the counter/reference electrode.

11. The system of claim 1, wherein the sensor is configured and arranged so that the mediator oxidizes the analyte and the half-wave potential of the redox mediator, as measured by cyclic voltammetry in 0.1 M NaCl at pH 7, is no more than about −

150 millivolts relative to the potential of the counter/reference electrode.

12. The system of claim 1, wherein the redox mediator is diffusible, and wherein, within the sensor, the effective diffusion coefficient of the redox mediator through the sample fluid is less than the effective diffusion coefficient of the analyte through the sample fluid and, preferably, at least ten times less than the effective diffusion coefficient of the analyte through the sample fluid.

13. The system of claim 1, wherein the redox mediator is diffusible, and wherein the diffusible mediator has a molecular weight of at least 5,000 daltons.

14. The system of claim 1, wherein the sensor is configured and arranged so that the redox mediator is more readily electrolyzed on the working electrode than the counter electrode.

15. The system of claim 1, wherein the sensor comprises a molar amount of the redox mediator that is, on a stoichiometric basis, no more than an average normal physiological amount of the analyte and, preferably, the sensor comprises a molar amount of the redox mediator that is, on a stoichiometric basis, no more than 20% of an average normal physiological amount of the analyte.

16. The system of claim 1, wherein the working electrode has a surface area of no more than about 0.01 cm² exposed in the sample chamber.

17. The system of claim 1, wherein the activity of the enzyme is no more than 1 unit/cm³.

18. The system of claim 1, wherein the redox mediator is diffusible, and wherein the sensor is configured and arranged so that the diffusible redox mediator precipitates when reacted at the counter electrode.

19. The system of claim 1, wherein the redox mediator is diffusible, and wherein the sensor is configured and arranged so that a mathematical product of the effective diffusion coefficient of the redox mediator and the concentration of the redox mediator is no more than 1×

10<sup>−

12</sup> moles cm<sup>−

1</sup> sec<sup>−

1</sup> when sample fluid fills the sample chamber.

20. The system of claim 1, wherein the redox mediator is diffusible, and wherein the diffusible redox mediator is disposed on the working electrode.

21. The system of claim 1, wherein the analyte-responsive enzyme is disposed on the working electrode.

22. The system of claim 1, wherein the sample fluid is blood from the finger of a subject.

23. The system of claim 1, wherein the sample fluid is blood from a region of a subject having a lower nerve end density as compared to a fingertip.

24. The system of claim 1, wherein the proximal end of the sensor comprises a first extension positioned at a first sample entry port and a second extension positioned at a second sample entry port.

25. A method for determining a concentration of an analyte in a sample, comprising the steps of:

(a) contacting a sample with a sensor, wherein the sensor comprises;

a first substrate having a proximal end and a distal end, the distal end being configured and arranged for insertion into a sensor reader;

a second substrate disposed over the first substrate;

a spacer disposed between the first and second substrates and defining a first aperture along the first side edge of the sensor, a second aperture along the second side edge of the sensor, and a sample chamber extending from the first aperture to the second aperture, wherein the sample chamber is sized to contain a volume of no more than about 1 μ

L of the sample;

a working electrode and a counter electrode disposed in the sample chamber, wherein the working electrode and the counter electrode are separated by a closest distance in a range of from 200 to 1000 μ

m; and

an analyte-responsive enzyme and a redox mediator disposed in the sample chamber;

(b) applying a first potential and a second potential to determine fill of the sample chamber with sample;

(c) applying a third potential to electrolyze the analyte, thereby generating an analyte signal; and

(d) determining the concentration of the analyte using the analyte signal.

26. The method according to claim 25, wherein determining the concentration of the analyte comprises determining the concentration of the analyte by coulometry using the sensor signal.

27. The method according to claim 25, wherein determining the concentration of the analyte comprises determining the concentration of the analyte by amperometry using the sensor signal.

28. The method according to claim 25, wherein determining the concentration of the analyte comprises determining the concentration of the analyte by potentiometry using the sensor signal.

29. The method according to claim 25, wherein determining the concentration of the analyte comprises determining the concentration of the analyte by chronoamperometry using the sensor signal.

30. The method according to claim 25, wherein determining the concentration of the analyte comprises determining the concentration of the analyte by chronopotentiometry using the sensor signal.

31. The method according to claim 25, wherein determining the concentration of the analyte comprises determining the concentration of the analyte by a Cotrell measurement technique using the sensor signal.

32. The method according to claim 25, further comprising:

providing calibration data on a batch of the electrochemical sensors to a measurement instrument, said calibration data comprising information related to a magnitude of a background charge for the batch of the electrochemical sensors;

wherein the step of determining the concentration of the analyte comprises determining the concentration of the analyte using the sensor signal and the calibration data.

33. The method according to claim 25, wherein the sample is a blood sample, and wherein the method further comprises obtaining the blood sample from a finger of a subject.

34. The method according to claim 25, wherein the sample is a blood sample, and wherein the method further comprises obtaining the blood sample from a region of a subject having a lower nerve end density as compared to a fingertip.

35. The method according to claim 34, wherein the region of a subject having a lower nerve end density as compared to a fingertip is selected from the group consisting of:

a forearm region, and a thigh region.

36. The method according to claim 25, wherein the proximal end of the sensor comprises a first extension positioned at a first sample entry port and a second extension positioned at a second sample entry port.