A light activated miniature formaldehyde sensor working at room temperature is fabricated by CdSO4 modified ZnO nanoparticles. The CdSO4 is deposited on the surface of the ZnO nanoparticles as a separated phase rather than doping into the lattice of ZnO. The Cd2+ and SO42− on the surface play a synergic effect for the high sensitivity to formaldehyde. The sensor shows high sensitivity to formaldehyde, with detection limit lower than 1 ppm while shows no response to ethanol and very weak response to acetone. With engineering efforts, a highly compact prototype formaldehyde sensor is obtained, which is very convenient for portable formaldehyde specific detection.
