A sensor implanted in tissues and including a sensing layer is fabricated by mixing the signal transduction enzyme with non-reactive components including buffer salts and fillers, and spin coating the enzyme onto a substrate. The signal transduction enzyme is crosslinked by introducing the coated substrate in a vacuum chamber. In the chamber, a crosslinker evaporates and is deposited onto the enzyme, therefore crosslinking the enzyme.

A sensor implanted in tissues and including a sensing layer is fabricated by mixing the signal transduction enzyme with non-reactive components including buffer salts and fillers, and spin coating the enzyme onto a substrate. The signal transduction enzyme is crosslinked by introducing the coated substrate in a vacuum chamber. In the chamber, a crosslinker evaporates and is deposited onto the enzyme, therefore crosslinking the enzyme.

A sensor implanted in tissues and including a sensing layer is fabricated by mixing the signal transduction enzyme with non-reactive components including buffer salts and fillers, and spin coating the enzyme onto a substrate. The signal transduction enzyme is crosslinked by introducing the coated substrate in a vacuum chamber. In the chamber, a crosslinker evaporates and is deposited onto the enzyme, therefore crosslinking the enzyme.

A sensor implanted in tissues and including a sensing layer is fabricated by mixing the signal transduction enzyme with non-reactive components including buffer salts and fillers, and spin coating the enzyme onto a substrate. The signal transduction enzyme is crosslinked by introducing the coated substrate in a vacuum chamber. In the chamber, a crosslinker evaporates and is deposited onto the enzyme, therefore crosslinking the enzyme.

A sensor implanted in tissues and including a sensing layer is fabricated by mixing the signal transduction enzyme with non-reactive components including buffer salts and fillers, and spin coating the enzyme onto a substrate. The signal transduction enzyme is crosslinked by introducing the coated substrate in a vacuum chamber. In the chamber, a crosslinker evaporates and is deposited onto the enzyme, therefore crosslinking the enzyme.

A method of testing a sample for the presence of nitrate or nitrite, the method comprising the steps of: forming a mixture by contacting the sample with a composition comprising hydrogen peroxide or a hydrogen peroxide precursor and a fluorescent indicator precursor capable of forming a fluorescent indicator in the presence of peroxynitrite; irradiating the mixture; and measuring fluorescence from the fluorescent indicator. The method may be carried out using a device in which the mixture in a channel or chamber 101 of a microfluidic device is irradiated by light from light source 103 and emission from the fluorescent indicator is detected by photodetector 105.

A sensor implanted in tissues and including a sensing layer is fabricated by mixing the signal transduction enzyme with non-reactive components including buffer salts and fillers, and spin coating the enzyme onto a substrate. The signal transduction enzyme is crosslinked by introducing the coated substrate in a vacuum chamber. In the chamber, a crosslinker evaporates and is deposited onto the enzyme, therefore crosslinking the enzyme.

A sensor implanted in tissues and including a sensing layer is fabricated by mixing the signal transduction enzyme with non-reactive components including buffer salts and fillers, and spin coating the enzyme onto a substrate. The signal transduction enzyme is crosslinked by introducing the coated substrate in a vacuum chamber. In the chamber, a crosslinker evaporates and is deposited onto the enzyme, therefore crosslinking the enzyme.