Screen-printed bienzymatic sensor based on sol-gel immobilized Nippostrongylus brasiliensis acetylcholinesterase and a cytochrome P450 BM-3 (CYP102-A1) mutant

Abstract

Here we describe the development of a bienzymatic biosensor that simplifies the sample pretreatment steps for insecticide detection, and enables the highly sensitive detection of phosphorothionates in food. These compounds evolve their inhibitory activity towards acetylcholinesterases (AChEs) only after oxidation which is performed in vivo by P450 monooxygenases. Consequently, phosphorothionates require a suitable sample pretreatment by selective oxidation to be detectable in AChE based systems. In this study, enzymatic phosphorothionate activation and AChE inhibition were integrated in a single biosensor unit. A triple mutant of cytochrome P450 BM-3 (CYP 102-A1) and Nippostrongylus brasiliensis AChE (NbAChE) were immobilized using a fluoride catalyzed sol-gel process. Different sol-gel types were fabricated and characterized regarding enzyme loading capacity and enzyme activity containment. The enzyme sol-gel itself already proved to be suitable for the highly sensitive detection of paraoxon and parathion in a spectrometric assay. A method for screen-printing of this enzyme sol-gel on thick film electrodes was developed. Finally, amperometric biosensors containing coimmobilized NbAChE and the cytochrome P450 BM-3 mutant were produced and characterized with respect to signal stability, organophosphate detection, and storage stability. The detection limits achieved were 1 μg/L for paraoxon and 10 μg/L for parathion in its oxidized form, which is according to EC regulations the highest tolerable pesticide concentration in infant food.