Rapid-response gas sensing element
A gas analysis sensing element and a method of making the sensing element are disclosed. In one embodiment, the sensing element includes cytochrome c embedded in a sol-gel matrix. The sol-gel matrix is either a thin film or a monolith. Parameters for creating such a sensing element, including protein concentration, sol-gel pore size, surface area for the monolith embodiment, sol-gel components, and processing temperature, are also disclosed.
1 . A method for detecting nitric oxide in a sample of exhaled breath at a concentration of 200 ppb or less, said method comprising:
contacting said exhaled breath in the gas phase with a xerogel monolith comprising cytochrome c encapsulated in a polymeric matrix, said xerogel monolith having a cytochrome c concentration of 1 mg/cc to 40 mg/cc, a pore diameter of 3.0 nm to 6.0 nm, and a surface area of 550 m 2 /g to 650 m 2 /g;
detecting a change in an optical property of said monolith as an indication of the binding of said nitric oxide to said cytochrome c; and
correlating any change so detected with the concentration of nitric oxide in said exhaled breath.
2 . The method of claim 1 wherein said nitric oxide concentration in said exhaled breath is 100 ppb or less.
3 . The method of claim 1 wherein said nitric oxide concentration in said exhaled breath is 50 ppb or less.
4 . The method of claim 1 wherein said pore diameter is 3.5 nm to 5.8 nm.
5 . The method of claim 1 wherein said cytochrome c concentration is from 20 mg/cc to 27 mg/cc.
6 . The method of claim 1 wherein said cytochrome c concentration is 25 mg/cc or less.
7 . The method of claim 1 wherein said cytochrome c concentration is from 8 mg/cc to 15 mg/cc.
8 . The method of claim 1 wherein said cytochrome c concentration is from 10 mg/cc to 12 mg/cc.
9 . The method of claim 1 wherein said monolith has a peak optical density of about 2.8 absorbance units at 400 nm.
10 . The method of claim 1 wherein said optical property is optical absorbance.