Conversion of inhibition biosensing to substrate-like biosensing for quinalphos selective detection

Since all of the organophosphorus pesticides (OPP) inhibit the cholinesterases with a common mechanism, it is still challenging to detect OPP selectively with inhibition-based biosensors. This study focuses on the conversion of a typical inhibition biosensing to a selective substrate-like biosensing. The interaction of quinalphos with plant-esterase involves not only a decrease in enzyme activity but also a heterolytic bond cleavage of quinalphos. The leaving group eliminated from quinalphos is an ideal biomarker due to its specificity in most OPP. Thus, using 2-hydroxyquinoxaline (HQO), the leaving group of quinalphos, as the biomarker and meso-tetra (4-sulfonatophenyl) porphine (TPPS4) as an optical probe, quinalphos can be selectively detected. The molecular recognition between TPPS4 and HQO leads to a considerable sensitivity of the detection. The spectral responses of TPPS4 show a linear dependence on quinalphos concentration in the presence of plant-esterase within the 0.01-1 mg kg(-1) range. The detection limit is 0.01 mg kg(-1), well below the maximum residue limits (MRLs) defined by European Union (0.05 mg kg(-1)) and China (0.2 mg kg(-1)).