Low concentration ammonia nanosensor

1. An electrochemical sensor for sensing ammonia, said sensor comprising:

a substrate having more than four electrodes disposed thereon; and

a carbon nanotube-polyaniline (CNT/PANI) film disposed on the substrate and in contact with at least two electrodes,

said CNT/PANI film comprising carbon nanotubes coated with a layer of polyaniline of thickness such that electron transport can occur along and/or between the carbon nanotubes; and wherein the average thickness of the polyanaline coating on the surface of the CNTs is less than the average diameter of the carbon nanotubes.

2. A method of making an electrochemical sensor for sensing a gaseous analyte, said method comprising:

preparing a solution of polyaniline (PANI) and camphorsulfonic acid (CSA) in chloroform;

preparing a solution of octadecylamine (ODA) functionalized carbon nanotubes (CNTs) in chloroform;

mixing the PANI/CSA solution and the ODA-functionalized CNT solution to make a CNT/PANI solution; and

depositing a CNT/PANI film on a substrate having at least two electrodes disposed thereon, such that the film is in contact with at least two electrodes,

wherein said film comprises carbon nanotubes coated with a layer of polyaniline of thickness such that electron transport can occur along and/or between the carbon nanotubes, and said film is formed by spin-coating the CNT/PANI solution.

3. A method according to claim 2 , wherein the concentration of PANI in the PANI/CSA solution is equal to the concentration of CNTs in the ODA-functionalized CNT solution.

4. A method according to claim 2 , wherein the CNT/PANI solution is a 50:50 mixture of PANI/CSA solution and ODA-functionalized CNT solution.

5. The method according to claim 2 , wherein the gaseous analyte is ammonia.

6. A method according to claim 5 , wherein the sensor is capable of sensing at least 1 ppb of ammonia.

7. A method according to claim 5 , said substrate having four platinum electrodes disposed thereon.

8. A method according to claim 5 , wherein the CNT/PANI film has an average thickness of 50-100 nm.

9. A method according to claim 5 , wherein the layer of polyaniline coating CNTs is transparent to electron tunneling.

10. A method according to claim 5 , wherein the average thickness of the polyaniline coating is less than the average diameter of the carbon nanotubes.

11. A method according to claim 9 , wherein the polyaniline coating has an average thickness of less than 10 nm.

12. A method according to claim 9 , wherein the diameter of the polyaniline-coated carbon nanotubes is greater than or equal to 10 nm and less than 50 nm.

13. A method for detecting a disease from analytes in a sample of human exhaled breath, comprising:

exposing a polyaniline (PANI)-carbon nanotube composite to a gaseous breath sample from a human, whose resistivity changes in response to ammonia present in the gaseous sample; and

detecting the change in resistivity of the sensor in response to ammonia in the gaseous sample, detecting a concentration of ammonia between 1 ppb and 200 ppb which is used to detect the presence of a disease.

14. The method according to claim 13 , further comprising using a sensor in the form of a miniaturized device.

15. The method according to claim 13 , comprising comparing the detected ammonia to a baseline value, and providing a digitized output of the concentration of ammonia.

16. An electrochemical sensor for sensing a gaseous analyte, said sensor comprising:

a substrate having at least two electrodes disposed thereon; and

a carbon nanotube-polyaniline (CNT/PANI) film disposed on the substrate and in contact with at least two electrodes,

said CNT/PANI film comprising carbon nanotubes coated with a layer of polyaniline of thickness such that electron transport can occur along and/or between the carbon nanotubes; wherein the wherein the polyaniline coating has an average thickness of less than 10 nm and wherein the average diameter of the polyaniline-coated carbon nanotubes is greater than or equal to 10 nm and less than 50 nm.

17. The electrochemical sensor of claim 16 wherein the average diameter of the polyaniline-coated carbon nanotubes is greater than or equal to 10 nm and less than 30 nm.

18. An electrochemical sensor for sensing ammonia, said sensor comprising:

a substrate having at least two electrodes disposed thereon; and

a carbon nanotube-polyaniline (CNT/PANI) film disposed on the substrate and in contact with at least two electrodes,

said CNT/PANI film comprising carbon nanotubes coated with a layer of polyaniline of thickness such that electron transport can occur along and/or between the carbon nanotubes; and wherein said sensor is capable of sensing at least 1 ppb of the ammonia.