Ultra-sensitive biosensor based on genetically engineered acetylcholinesterase immobilized in poly (vinyl alcohol)/Fe–Ni alloy nanocomposite for phosmet detection in olive oil

•Acetylcholinesterase was intrapped in Fe/Ni nanopowder modified photopolymer.•Fe/Ni nanocomposite allows ampifying the current and lowering the applied potential.•The biosensor allowed highly sensitive detection of phosmet, the LOD was 0.1nM.•Recovery rate of phosmet was 96% after liquid–liquid extraction from olive oil. An ultra-sensitive screen-printed biosensor was successfully developed for phosmet detection in olive oil, based on a genetically-engineered acetylcholinesterase (AChE) immobilized in a azide-unit water-pendant polyvinyl alcohol (PVA-AWP)/Fe–Ni alloy nanocomposite. Fe–Ni not only allowed amplifying the response current but also lowering the applied potential from 80mV to 30mV vs Ag/AgCl. The biosensor showed a very good analytical performance for phosmet detection, with a detection limit of 0.1nM. This detection limit is lower than the allowable concentrations set by international regulations. In addition to the good reproducibility, operational and storage stability, the developed biosensor was successfully used for the determination of phosmet in olive oil samples without any laborious pre-treatment. The phosmet recovery rate was about 96% after a simple liquid–liquid extraction.