Superhydrophobic n-octadecylsiloxane (PODS)-functionalized PDA-PEI film as efficient water-resistant sensor for ppb-level hexanal detection

The detection of hexanal vapor in ppb (part per billion) concentration is an unresolved and indispensable issue. Here we report a polydopamine-polyethyleneimine (PDA-PEI) copolymer film with rich imino groups to sense 50 ppb hexanal vapor through the formation of the reversible hydrogen bonds with hexanal. We found that the water-resistance could be further improved by attaching superhydrophobic n-octadecylsiloxane (PODS) onto the surface of PDA-PEI film. The chemical adsorption mode and the core role of imino group for the hexanal detection have been validated by combining experiment methods with theory calculations. A quartz crystal microbalance (QCM) platform modified with this film was employed as a hexanal vapor sensor under ambient conditions, which possessed several advantages including the high response of 34.8 Hz to 250 ppb hexanal, low detection limit of 50 ppb hexanal at 25 degrees C, and good water-resistance.