Enzymatic toxic gas sensor

• US 4,525,704 A
• Filed: 11/09/1983
• Issued: 06/25/1985
• Est. Priority Date: 11/09/1983
• Status: Expired due to Term

• Current Assignee: Environmental Technologies Group, Inc.
• Original Assignee: Allied Corp. (Honeywell International Inc.)
• Inventors: Schmidt, John C., Campbell, Donald N.
• Primary Examiner(s): Kaplan, G. L.
• Assistant Examiner(s): Nguyen, Nam X.
• Application Number:
  US06/550,272
• Time in Patent Office: 594 Days
• Field of Search: 204/1 T, 204/1 E, 204/402, 204/403, 204/412, 204/415, 435/291, 435/287, 435/817, 435/20, 435/18, 340/632
• US Class Current: 340/632
• CPC Class Codes: C12M 21/18 Apparatus specially designed for the use of free, immobilized or carrier-bound enzymes
• CPC Class Codes: C12M 41/34 of gas
• CPC Class Codes: C12Q 1/005 involving specific analytes or enzymes including groups of enzymes, e.g. oxydases; C12Q1/004 takes precedence
• CPC Class Codes: C12Q 1/46 involving cholinesterase
• CPC Class Codes: Y10S 435/817 Enzyme or microbe electrode

Abstract

An enzymatic toxic gas sensor 10 having a plurality of parallel planar surfaces and a buffered electrolyte reservoir 44. The buffered electrolyte is conveyed by means of diffusion to a substrate 28 to dissolve the substrate. The substrate diffuses to an immobilized enzyme where it is hydrolyzed if the enzyme is active. An electrochemical cell continuously monitors the hydrolyzed substrate concentration which is an indication of the enzymatic activity and presence of toxic gas. A circuit means responds to the current output of the electrochemical cell to indicate the presence or absence of a toxic gas. The shelf life of the sensor is extended by means of a separator for maintaining the enzyme dry and inactive. The enzyme in the preferred embodiment is acetylcholinesterase (AcHe).

Claims

1. A enzymatic toxic gas sensor wherein the chemical reactions therein are activated by diffusion within the sensor, said sensor comprising:

a reservoir containing a buffered electrolyte;

a wick attached at one end thereof to said reservoir;

a porous membrane having one broadside adapted for interfacing with the ambient air;

a structure attached to the other broadside of said membrane, said structure having an enzyme covalently attached thereto;

an electrochemical cell means having a sensing electrode, a reference electrode and a counter electrode;

said sensing electrode spaced from said structure and adapted to react with reaction products of said enzyme to generate an electrical current;

substrate means adapted to receive the other end of said wick and containing a substrate which is dissolvable by said buffered electrolyte and diffuses to said enzyme to react with said enzyme in the absence of toxic gases; and

circuit means responsive to said electrochemical cell to generate a signal of one value due to the presence of toxic gases for activating an alarm means and a signal of another value due to the absence of toxic gases.

2. A sensor according to claim 1 additionally including:

separator means interposing said reservoir and said substrate means to prevent a reaction therebetween; and

a pin actuation means operatively connected to said separator means for removing said separator means when said pin is removed from the sensor.

3. A gas sensor according to claim 1 wherein said structure contains acetylcholinesterase (AcHe) covalently coupled to glass beads attached to the other broadside of said membrane.

4. A gas sensor according to claim 3 wherein said alarm means is responsive to the deactivation of said acetylcholinesterase by means of a toxic gas.

5. The apparatus of claim 1 wherein said enzyme includes yeast alcohol dehydrogenase.

6. A gas sensor according to claim 1 wherein said alarm means is responsive to the deactivation of said enzyme by means of a toxic gas.

7. A dual enzymatic toxic gas sensor wherein the chemical reactions therein are activated by diffusion within the sensor, said sensor comprising:

a first sensor having;

a reservoir containing a buffered electrolyte;

a wick attached at one end thereof to said reservoir;

a porous membrane having one broadside adapted for interfacing with the ambient air;

a structure attached to the other broadside of said membrane, said structure having an enzyme covalently attached thereto;

an electrochemical cell means having a sensing electrode, a reference electrode and a counter electrode;

said sensing electrode spaced from said structure and adapted to react with reaction products of said enzyme to generate an electrical current;

substrate means adapted to receive the other end of said wick and containing a substrate which is dissolvable by said buffered electrolyte and diffuses to said enzyme to react with said enzyme in the absence of toxic gases;

a second sensor having;

a reservoir containing a buffered electrolyte;

a wick attached at one end thereof to said reservoir;

a porous membrane having one broadside adapted for interfacing with the ambient air;

removable cover means normally covering said one broadside from interfacing with ambient air and adaptable to be removed therefrom;

a structure attached to the other broadside of said membrane, said structure having an enzyme covalently attached thereto;

an electrochemical cell means having a sensing electrode, a reference electrode and a counting electrode;

said sensing electrode spaced from said structure and adapted to react with reaction products of said enzyme to generate an electrical current;

substrate means adapted to receive the other end of said wick and containing a substrate which is dissolvable by said buffered electrolyte and diffuses to said enzyme to react with said enzyme in the absence of toxic gases; and

circuit means including a bridge circuit, summing means and alarm means responsive to each of said electrochemical cells from said first and second sensors to generate a signal of one value due to the presence of toxic gases and a signal of another value due to the absence of toxic gases for activating said alarm means and responsive to the removal of said cover means to generate one of said signals in response to the electrical current from said electrochemical cell in said second sensor.

8. A sensor according to claim 7 additionally including:

separator means interposing each of said reservoir and said substrate means to prevent a reaction therebetween; and

a pin actuation means operatively connected to each of said separator means for removing said separator means when said pin is removed from the sensor.

9. A gas sensor according to claim 7 wherein each of said structures contains acetylcholinesterase (AcHe) covalently coupled to glass beads attached to the other broadside of said membrane.

10. A gas sensor according to claim 9 wherein said alarm means is reponsive to the deactivation of said acetylcholinesterase by means of a toxic gas.

11. Apparatus for detecting certain toxic gases in an ambient gas comprising:

a substrate,

a pouch enclosing said substrate,

a pouch solvent positioned in said pouch for dissolving said substrate,

said pouch including a porous membrane in a wall of said pouch,

said pouch solvent and dissolved substrate positioned in contact with said porous membrane to permit said dissolved substrate to diffuse through said porous membrane,

a buffered electrolyte positioned in contact with said porous membrane, whereby said substrate diffusing through said porous membrane dissolves into said electrolyte,

an immobilized enzyme in contact with said buffered electrolyte to catalyze a reaction with said dissolved substrate to form reaction products,

means for dissolving said toxic gases from an ambient gas into said electrolyte to permit them to inhibit said enzyme,

an electrochemical cell means having a sensing electrode, a reference electrode and a counter electrode;

said sensing electrode spaced from said immobilized enzyme and adapted to react with reaction products of said substrate catalyzed by said enzyme to generate an electrical current;

circuit means coupled to said electrochemical cell to generate a signal indicative at first times of an ongoing catalyzed reaction and at second times of a diminished catalyzed reaction due to an inhibited enzyme.

12. The apparatus of claim 11 wherein said porous membrane includes polypropylene.

13. The apparatus of claim 11 wherein said porous membrane includes PTFE (polytetrafluoroethylene).

14. The apparatus of claim 11 wherein said buffered electrolyte includes tris-(hydroxymethyl) aminomethane.

15. The apparatus of claim 11 further including filter paper to position said buffered electrolyte.

16. The apparatus of claim 11 wherein said substrate includes acetylthiocholine perchlorate.

17. The apparatus of claim 11 wherein said porous membrane passes by diffusion approximately 2.0×

10^-8 moles per minute of said substrate.

18. The apparatus of claim 11 wherein said enzyme includes cholinesterase.

19. The apparatus of claim 11, wherein said enzyme includes yeast alcohol dehydrogenase.