A Portable ppb-Level Formaldehyde Sensor for Real-Time Air Quality Monitoring

We report the development of a battery-driven, portable, and ultrasensitive optical gas sensor for parts per billion (ppb)-level formaldehyde (H2CO) diagnostics. The sensor consists of an interband cascade laser exploiting the intense H2CO absorption line at 3.6 mu m, an open-path multipass gas cell with 26.4-m pathlength, and homemade electronics for signal processing, data acquisition, and results display. Besides the advantage of being interference-free from other atmospheric constituents, the Allan deviation analysis reveals a minimum detection limit (MDL) of 1.42 ppb at a time resolution of 0.2 s. This limit can be enhanced to 43 parts per trillion (ppt) with an average time of 230 s. Ultimately, we successfully showcased the practical use of the portable sensor for detecting indoor H2CO.