Multi-pin chemiresistors for microchemical sensors

• US 7,179,421 B1
• Filed: 01/23/2003
• Issued: 02/20/2007
• Est. Priority Date: 01/24/2002
• Status: Expired due to Fees

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Ho, Clifford K.
• Primary Examiner(s): Warden; Jill
• Assistant Examiner(s): SINES, BRIAN J
• Application Number:
  US10/349,689
• Time in Patent Office: 1,489 Days
• Field of Search: 422/50, 422/68.1, 422/82.01, 422/82.02, 422/83, 422/88, 422/98, 436/43, 436139-143, 436/149, 73/10.1, 73/10.2
• US Class Current: 422/82.02
• CPC Class Codes: G01N 27/126 comprising organic polymers
• CPC Class Codes: Y10T 436/11 Automated chemical analysis
• CPC Class Codes: Y10T 436/21 Hydrocarbon
• CPC Class Codes: Y10T 436/212 Aromatic
• CPC Class Codes: Y10T 436/214 Acyclic [e.g., methane, octane, isoparaffin, etc.]
• CPC Class Codes: Y10T 436/218 Total hydrocarbon, flammability, combustibility [e.g., air-fuel mixture, etc.]

Abstract

A multi-pin chemiresistor for use in microchemical sensors. A pair of free-standing, bare wires is supported by an electrically insulating support, and are oriented parallel to each other and spaced closely together. A free-standing film of a chemically sensitive polymer that swells when exposed to vapors of a volatile chemical is formed in-between the pair of closely-spaced wires by capillary action. Similar in construction to a thermocouple, this “chemicouple” is relatively inexpensive and easy to fabricate by dipping the pair of bare wires into a bath of well-mixed chemiresistor ink. Also, a chemiresistor “stick” is formed by dipping an electrically insulating rod with two or more linear or spiral-wrapped electrical traces into the bath of well-mixed chemiresistor ink, which deposits a uniform coating of the chemically sensitive polymer on the rod and the electrical traces. These “sticks” can be easily removed and replaced from a multi-chemiresistor plug.

Claims

1. A chemiresistor, comprising:

an electrically insulating support member;

two or more free-standing bare wires each having a proximal end supported by the support member, wherein the wires are oriented substantially parallel to each other, and are separated from each other by a small distance; and

a chemically sensitive polymer attached to, and suspended in-between, the two or more free-standing bare wires.

2. The chemiresistor of claim 1, wherein the chemically sensitive polymer comprises a material that swells when exposed to vapors of a volatile compound.

3. The chemiresistor of claim 1, wherein the chemically sensitive polymer comprises conductive particles embedded in a polymer matrix selected from the group consisting of poly(n-vinyl pyrrolidone), poly(vinyl alcohol), poly(ethylene-vinyl acetate), poly(isobutylene), poly(n-vinyl pyrrolidone), poly(epichlorohydrin), ethyl cellulose, poly(chloroprene), poly(diphenoxyphosphazine, and poly(caprolactone).

4. The chemiresistor of claim 1, comprising three free-standing bare wires.

5. The chemiresistor of claim 1, comprising four free-standing bare wires.

6. The chemiresistor of claim 5,

wherein two of the four free-standing bare wires are grouped together into a first chemiresistor pair, and the other two wires are grouped together into a second chemiresistor pair;

wherein the same chemically sensitive polymer attached to, and suspended in-between, each pair of free-standing bare wires; and

further wherein an overcoating of a chemically-selective material surrounds and covers the chemically sensitive polymer on only one of the two chemiresistor pairs, which can serve as a reference chemiresistor element.

7. The chemiresistor of claim 6, wherein the chemically-selective material comprises a material that allows water vapor to permeate through, while blocking other chemical vapors from permeating.

8. The chemiresistor of claim 7, wherein the chemically-selective material comprises a proton exchange membrane or Naflon™

.

9. The chemiresistor of claim 1, wherein the support member comprises a cylindrical plug comprising two or more male electrical connectors on the end opposite from the end supporting the two or more free-standing bare wires.

10. The chemiresistor of claim 1, wherein the spacing between the two or more free-standing bare wires is sufficiently close so as to permit a chemiresistive ink to wet both conductors due to capillary action during fabrication, and subsequently form a dried, free-standing polymer film suspended in-between or inside of the two or more free-standing bare conductors.

11. The chemiresistor of claim 1, wherein the spacing between the two exposed bare wires is less than approximately 100 microns.

12. The chemiresistor of claim 1, wherein the length of a conductor is at least ten times the spacing between the two or more free-standing bare wires.

13. The chemiresistor of claim 1, wherein the two or more free-standing bare wires are arranged in a U-shaped geometry, where the distal end of each wire is supported by the electrically insulating support member.

14. A chemiresistor, comprising:

a bundle of two or more insulated wires, each wire having a segment of free-standing bare wire;

wherein the two or more segments of bare wires are oriented substantially parallel to each other, and are separated from each other by a small distance; and

a chemically sensitive polymer attached to, and suspended in-between, the two or more segments of free-standing bare wires.

15. The chemiresistor of claim 14, further comprising a spacer disposed between the two or more insulated wires.

16. The chemiresistor of claim 14, further comprising a hollow, cylindrical support tube surrounding and supporting the bundle of two or more insulated wires.

17. The chemiresistor of claim 16, wherein the support tube comprises heat-shrinkable plastic tubing that has been heat-shrunk, thereby compressing and holding the bundle of wires together.

18. A chemiresistor, comprising:

two or more free-standing bare conductors, oriented substantially parallel to each other, and separated from each other by a small distance; and

a porous material disposed in-between, and supported by, the two or more free-standing bare conductors;

wherein a chemically sensitive polymer is disposed throughout the porous material, and contacts the two or more free-standing bare conductors.

19. The chemiresistor of claim 18, wherein the conductors comprise plates.

20. A chemiresistor stick, comprising:

an electrically insulating rod;

two or more conductors disposed on the outer surface of the rod, wherein the conductors are oriented substantially parallel to each other, and are separated from each other by a small distance; and

a chemically sensitive polymer disposed on the outer surface of the rod, contacting the two or more conductors.

21. The chemiresistor of claim 20, wherein the rod comprises a cylindrical cross-section whose length is greater than about five times its diameter.

22. The chemiresistor of claim 21, wherein each conductor has the shape of a straight line oriented parallel to the long direction of the rod.

23. The chemiresistor of claim 21, comprising four conductors disposed evenly around the circumference of the rod.

24. The chemiresistor of claim 20, wherein the two or more conductors wrap around the outer surface of the rod in a dual-track, spiral wrapped geometry.

25. The chemiresistor of claim 20, wherein the rod comprises a square or rectangular cross-section.

26. The chemiresistor of claim 25, wherein the two or more conductors comprise thick film or thin film metallized traces.

27. A microchemical sensor, comprising a plurality of chemiresistor sticks supported by an electrically insulating plug, wherein each chemiresistor stick comprises:

an electrically insulating rod;

two or more conductors disposed on the outer surface of the rod, wherein the conductors are oriented substantially parallel to each other, and are separated from each other by a small distance; and

a chemically sensitive polymer disposed on the outer surface of the rod, contacting the two or more conductors.

28. The microchemical sensor of claim 27, wherein each rod comprises a cylindrical cross-section, and wherein each two or more conductors wrap around the outer surface of each rod in dual-track, spiral wrapped geometry.

29. The microchemical sensor of claim 27, wherein the plurality of chemiresistor sticks comprises four chemiresistor sticks.

30. The microchemical sensor of claim 29, wherein each chemiresistor stick comprises a different chemically sensitive polymer matrix.

31. The microchemical sensor of claim 29, wherein each chemiresistor stick is removable from the electrically insulating plug.