Gas sensor element
Described herein are sensor elements for detecting the presence of organic materials comprising a boron doped n-type semiconductor material with decrease in resistivity upon organic materials exposure with increase in resistivity upon organic materials exposure.
1. A method for determining acetone in a subject's breath comprising exposing a mammalian breath sample to a gas sensor, the sensor comprising a gas sensor element comprising:
a first electrode and second electrode, wherein the first electrode and the second electrode are separated by a gap of about 1 to about 10 mils; and
a polycrystalline n-type semiconductor material comprising:
epsilon phase WO 3 that is doped with boron; or
gamma phase WO 3 mixed with CeO 2 ;
wherein the polycrystalline n-type semiconductor material physically contacts both the first and second electrodes; and
wherein the presence of acetone is detected by a change in resistivity across the sensor.
2. The method of claim 1 , wherein the boron is present at about 0.001% to about 1% by weight of the polycrystalline n-type semiconductor material.
3. The method of claim 1 , wherein the polycrystalline n-type semiconductor material is combustion synthesized.
4. The method of claim 1 , wherein the polycrystalline n-type semiconductor is at a temperature of about 190° C. to about 360° C.
5. The method of claim 1 , further comprising a noble metal mixed with the polycrystalline n-type semiconductor material.
6. The method of claim 5 , wherein the noble metal is palladium, gold, platinum or iridium.
7. The method of claim 1 , wherein the gamma phase WO 3 is mixed with CeO 2 .
8. The method of claim 7 , wherein the polycrystalline n-type semiconductor material is exposed to blue light.
9. The method of claim 8 , wherein the polycrystalline n-type semiconductor material is at a temperature of about 10° C. to about 40° C.
10. The method of claim 8 , wherein the gamma phase WO 3 mixed with CeO 2 is about 40-60 molar % WO 3 .
11. The method of claim 1 , wherein the polycrystalline n-type semiconductor material is ball milled.
12. The method of claim 1 , wherein the gas sensor operating temperature is from about 10° C. to about 50° C. and the gas sensor element is exposed to blue light.
13. The method of claim 1 , wherein the gas sensor operating temperature is about 190° C. to about 360° C.
14. The method of claim 13 , wherein the sensor is not exposed to blue light.
15. The method of claim 13 , wherein the gas sensor operating temperature is from about 280° C. to about 360° C., and the gas sensor is more sensitive to isoprene than to acetone.
16. The method of claim 1 , wherein the gas sensor operating temperature is from about 180° C. to about 240° C., and the gas sensor is more sensitive to acetone than to isoprene.