Three-layered membrane for use in an electrochemical sensor system

• US 5,773,270 A
• Filed: 05/17/1994
• Issued: 06/30/1998
• Est. Priority Date: 03/12/1991
• Status: Expired due to Fees

• Current Assignee: Chiron Corporation (Bayer AG)
• Original Assignee: Chiron Corporation (Bayer AG)
• Inventors: Sogin, David, D'Orazio, Paul A.
• Primary Examiner(s): Naff, David M.
• Application Number:
  US08/245,194
• Time in Patent Office: 1,505 Days
• Field of Search: 435/177, 435/179, 435/180, 435/288, 435/817, 435/14, 435/25, 435/27, 204/403
• US Class Current: 204/403.01
• CPC Class Codes: C12N 11/12 Cellulose or derivatives thereof
• CPC Class Codes: C12Q 1/006 for glucose
• CPC Class Codes: Y10S 435/817 Enzyme or microbe electrode

Abstract

A system for electrochemical measurement of glucose concentration in an undiluted test sample, e.g. blood is provided containing a sensor including a three-layered contiguous membrane. The membrane has a thickness of 50 to 130 microns, and is composed of a 1 to 10 micron thick first layer, a 10 to 30 micron thick second layer having an average pore diameter of 15 nanometers and a 40 to 80 micron thick third layer containing glucose oxidase. The third layer is less dense than the first and second layers and the first layer is more dense than the second layer. The layers of the membrane are fused together such that no clear distinction can be made between the layers at the boundary. The sensor is calibrated in a standard glucose solution which includes catalase as a hydrogen peroxide scavenger, and the sensor has a response that is linear throughout the concentration range of glucose in an undiluted sample. In one embodiment, the system is a polarographic cell structure containing an electrically insulating receptacle, an electrode mounted in the receptacle, and the three-layered membrane.

Claims

1. A three-layered contiguous membrane prepared by the method comprising:

(a) providing a first solution comprising a first polymer dissolved in an inert organic solvent and casting said first solution onto a first inert support surface wherein said support is unreactive with said first polymer and said support does not form a bond to said first polymer,

(b) permitting said first solution to form a 1 to 10 micron film and thereby obtaining a first layer,

(c) providing a second polymer dissolved in a second inert organic solvent and mixing said second polymer with a nonsolvent for said second polymer to obtain a second solution,

(d) casting a 0.30 mm wet thickness of said second solution onto said first layer, and thereafter permitting said second solution to dry to form a second layer having an average pore diameter of about 15 nanometers and a thickness ranging from 10 to 30 microns,

(e) providing a third solution comprising a third polymer dissolved in a third inert organic solvent, mixing said third solution with a nonsolvent for said third polymer and with a water solution of glucose oxidase to obtain a dispersion and thereafter casting said dispersion onto said second layer, and thereafter permitting said third polymer to dry to form a 40 to 80 micron third layer,

wherein said third layer is less dense than said first and second layers and said first layer is more dense than said second layer and wherein said layers of the membrane are fused together such that no clear distinction can be made between the layers at the boundary and the boundary between the layers is a diffusion zone and wherein said membrane has a thickness of from 50 to 130 microns.

2. The membrane according to claim 1 wherein said first layer has a thickness of from about 2 to about 5 microns and said second layer has a thickness of from about 15 to about 25 microns.

3. The membrane according to claim 1 wherein said second layer is about 23 microns in thickness and said first layer is about 2 microns in thickness and said third layer is about 65 microns in thickness.

4. The membrane according to claim 1 wherein said membrane has an overall thickness of about 90 microns and said second layer is about 23 microns in thickness.

5. The membrane according to claim 1 wherein said second layer is about 23 microns in thickness.

6. The membrane according to claim 5 wherein said first, second, and third inert organic solvents are the same and said first and second polymers are the same.

7. The membrane according to claim 1 wherein said first, second, and third inert organic solvent is a ketone.

8. The membrane according to claim 7 wherein said water solution of glucose oxidase further comprises ethanol.

13. A system for measuring glucose concentration in a test sample, said system comprising:

(a) a hydrogen peroxide electrode adapted to generate a signal,

(b) the three-layered contiguous membrane as recited in claim 1, and

(c) a calibrating solution comprising a known concentration of glucose and a hydrogen peroxide scavenger.

14. The system according to claim 13 wherein in (c) said hydrogen peroxide scavenger is catalase.

15. The system according to claim 14 wherein in (c) said catalase is present in an amount of about 120 kU/ml of said calibrating solution.

9. A polarographic cell structure for use in a electrochemical analysis of an unknown, said cell comprising an electrically insulating receptacle;

an electrode mounted in said receptacle, and a three-layered membrane, said membrane prepared by a method comprising;

(a) providing a first solution comprising a first polymer dissolved in an inert organic solvent and casting said first solution onto a first inert support surface wherein said support is unreactive with said first polymer and said support does not form a bond to said first polymer,

(b) permitting said first solution to form a 1 to 10 micron film and thereby obtaining a first layer,

(c) providing a second polymer dissolved in a second inert organic solvent and mixing said second polymer with a nonsolvent for said second polymer to obtain a second solution,

(d) casting a 0.30 mm wet thickness of said second solution onto said first layer, and thereafter permitting said second solution to dry to form a second layer having an average pore diameter of about 15 nanometers and a thickness ranging from 10 to 30 microns,

(e) providing a third solution comprising a third polymer dissolved in a third inert organic solvent, mixing said third solution with a nonsolvent for said third polymer and with a water solution of glucose oxidase to obtain a dispersion and thereafter casting said dispersion onto said second layer, and thereafter permitting said third polymer to dry to form a 40 to 80 micron third layer,

wherein said third layer is less dense than said first and second layers and said first layer is more dense than said second layer and wherein said layers of the membrane are fused together such that no clear distinction can be made between the layers at the boundary and the boundary between the layers is a diffusion zone and wherein said membrane has a thickness of from 50 to 130 microns.

10. The polarographic cell structure according to claim 9 wherein in said membrane, said first layer has a thickness of from about 2 to about 5 microns and said second layer has a thickness of from about 15 to about 25 microns and said first and second polymers are the same and said first, second and third inert solvents are the same.

11. The polarographic cell structure according to claim 10 wherein in said membrane, said second layer is about 23 microns in thickness.

12. The polarographic cell structure according to claim 11 wherein in said membrane, said third layer is about 65 microns in thickness, and said first layer is about 2 microns and said overall thickness of said membrane is 90 microns.