Sample conditioning and environmental control techniques for gas sensor
The present invention is a system and method of conditioning the sample and surrounding environment of an exhaled breath sensor. It includes (i) using a particular molecular sieve for a triple purpose: (a) maintaining the sensor at a constant relative humidity during storage, (b) equilibrating the incoming breath stream to the same relative humidity as the sensor, and (c) eliminating the analyte from the environment around the sensor during storage. The present invention also includes removal of interfering components from the exhaled breath, such as carbon dioxide, as well as a thermal management technique.
1. A system for detecting trace amounts of nitric oxide in exhaled breath, comprising:
a. a sensing element that is responsive to a trace amount of nitric oxide in exhaled breath; and
b. a desiccant surrounding said sensing element.
2. The system according to claim 1 , wherein said desiccant is a molecular sieve.
3. The system according to claim 2 , wherein said molecular sieve comprises particles having an approximate pore size of 3 Angstroms.
4. The system according to claim 1 , wherein said sensing element comprises cytocbrome-c in a sol-gel.
5. The system according to claim 1 , additionally comprising a scrubber for removing an interfering substance.
6. The system according to claim 5 , wherein said interfering substance is carbon dioxide.
7. The system according to claim 5 , wherein said scrubber comprises activated alumina.
8. The system according to claim 1 , additionally comprising a heater or cooler for controlling the temperature of said sensing element.
9. A method for detecting trace amounts of nitric oxide in exhaled breath, comprising:
a. providing a sensor, said sensor comprising a sensing element that is responsive to a trace amount of nitric oxide in exhaled breath;
b. surrounding said sensing element with a desiccant to maintain a predetermined sensor humidity level in said sensor during storage;
c. capturing an exhaled breath stream from a subject into said sensor; and
d. conditioning said breath stream to a humidity level that is substantially equivalent to said predetermined sensor humidity level.
10. The method according to claim 9 , wherein said desiccant is a molecular sieve.
11. The method according to claim 9 , additionally comprising removing said analyte from said sensor during storage.
12. The method according to claim 11 , wherein a molecular sieve is used for removing said analyte from said sensor during storage.
13. The method according to claim 9 , wherein said predetermined sensor humidity level is between 10 to 1000 ppm.
14. The method according to claim 9 , additionally comprising removing an interfering substance from said breath stream with a scrubber.
15. The method according to claim 14 , wherein said interfering substance is carbon dioxide.
16. The method according to claim 15 , wherein said scrubber comprises activated alumina.
17. A system for detecting trace amounts of nitric oxide in exhaled breath, comprising:
a. a sensing element that is responsive to a trace amount of nitric oxide in exhaled breath;
b. a temperature control device within sufficient proximity to said sensing element to control the temperature of said sensing element, and
c. a molecular sieve surrounding said sensing element.
18. The system according to claim 17 , wherein said temperature control device is a heater or cooler.
19. The system according to claim 18 , wherein said heater or cooler maintains said exhaled breath and said sensing element at a predetermined temperature within 1.0° C.
20. The system according to claim 19 , wherein said predetermined temperature is approximately 20-40 C.
21. The system according to claim 17 , additionally comprising a scrubber.