NADH-fluorometric biochemical gas sensor (bio-sniffer) for assessment of indoor air quality

A fiber-optic biochemical gas sensor (bio-sniffer) for assessment of indoor formaldehyde was fabricated and tested. The bio-sniffer measures formaldehyde vapor as fluorescence of reduced nicotinamide adenine dinucleotide (NADH), which is the product of formaldehyde dehydrogenase (FALDH) reaction. Usually, an enzyme loses its specific activity in the gas phase. This makes biochemical gas monitoring difficult. We used a micro flow-cell with a FALDH immobilized membrane to prevent the FALDH from deactivation. An ultraviolet light emitting diode (UV-LED) with peak emission of 335nm was employed as an excitation light source. Emission of the UV-LED was introduced to the optode through an optical fiber and fluorescence of NADH was picked up coaxially at the optode. In order to improve the sensitivity, a photomultiplier tube was utilized as a photodetector. Consequently, continuous FA monitoring with biochemical method was successfully conducted with high sensitivity and high selectivity. A real-sample test was also carried out with the bio-sniffer. According to the results, it is expected to be useful in fast and convenient monitoring of indoor FA.