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 °C, and good water-resistance.