Ppb-level formaldehyde sensor utilizing a compact 3D-printed differential photoacoustic cell and a 320 nm UV laser

Precise measurement of formaldehyde (H₂CO) is a vital defense line for health, crucial for risk warning and prevention of major diseases like leukemia and cancer. The cross-interference of commercial electrochemical and metal oxide semiconductor sensors is grievous for H₂CO sensing. Spraying disinfection alcohol, culinary steam, or even perfume may mistakenly trigger warnings. In this work, a low-cost 3D-printed differential photoacoustic cell (PAC) with a ultraviolet (UV) laser is developed for trace H₂CO detection based on the photoacoustic spectroscopy (PAS) technology. A 3D-printed differential PAC is an integrated structure composed of two differential channels, two gas buffer chambers, a gas inlet and a gas outlet. Two steel tubes with identical length and an internal diameter of 4 mm are inserted into two differential channels to enhance the photoacoustic signal, respectively. Consequently, the differential PAC has a resonant frequency of 3775.5 Hz and a Q-factor of 27, with a minimal gas sample requirement of only 7.3 mL and a weight of 32.4 g. A 1σ detection limit of 1.03 ppm is achieved using a 320 nm 10 mW UV laser with an integration time of 1 s. An Allan-Werle deviation analysis indicates that the detection limit can be improved to 68.5 ppb at the optimal integration time of 969 s.