Sensitive amperometric biosensor for dichlorovos quantification: Application to detection of residues on apple skin

This paper presents the construction of an amperometric biosensor for the highly sensitive detection of the organophosphorus insecticide dichlorvos, based on the inhibition of acetylcholinesterase (AChE). The sensitivity of three AChEs from different sources were tested and compared: AChEs from Electric eel (Ee) and genetically engineered (B394) and wild type (B1) from Drosophila melanogaster (Dm). The enzymes were immobilized by entrapment in a photocrosslinkable PVA-SbQ polymer on a screen printed graphite electrode. The enzyme activity was estimated amperometrically at 100mV versus Ag/AgCl by measuring the thiocholine produced by the enzymatic hydrolysis of the acetylthiocholine substrate using cobalt phthalocyanine as electron mediator. The pesticide was measured in the presence of 5% acetonitrile without loss of enzyme activity. The best sensitivity was achieved with the Dm mutant B394 with a detection limit of 7x10(-11)M as compared to 1x10(-8)M with the B1 Dm and 6x10(-7)M with the Ee. The B394 biosensor was used to quantify dichlorvos in a sample of skin apple after extraction with acetonitrile.