PVDF-stimulated surface engineering in ZnO for highly sensitive and water-stable hydrazine sensors

Sensors based on multifunctional n-type metal oxide semiconductors are attracting significant interest in environmental monitoring owing to their distinct characteristics including low production cost, high detection response to different noxious analytes, nontoxic nature, and acceptable biocompatibility. Herein, we present an innovative approach that utilizes surface functionalization on ZnO thin-film transistor (TFT)-type sensors with a fluoropolymer, poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to realize highly sensitive and water-stable liquid-phase sensors. ZnO sensors laminated with PVDF-HFP thin films demonstrate exceptional repeatable stability to DI water and liquid-phase hydrazine, indicating excellent sensitivity in addition to low hydrazine-detection limits approaching 0.01 nM (sub-ppt level) under ambient conditions. This detection limit is five orders of magnitude less than that of the legal limit for an 8 h exposure time-weighted average for hydrazine. Moreover, relatively acceptable repeatability and reproducibility of the sensors were guaranteed over 96% of their initial base current with hydrazine for a month. This outstanding sensing performance is attributed to the enhanced surface interaction between PVDF-HFP with a strong dipole moment and hydrazine, which is completely discriminated from the universal detection mechanism associated with oxygen ion species in ZnO.