Mercaptobenzothiazole on gold biosensor systems for organophosphate and carbamate pesticide compounds

Abstract

Organophosphate and carbamate pesticides are powerful neurotoxins that impede the activity of cholinesterase enzyme leading to severe health effects. This study firstly reports the development, characterisation, and application of thick-film acetylcholinesterase (AChE) biosensors based on a gold electrode modified with a mercaptobenzothiazole (MBT) self-assembled monolayer and either poly(omethoxyaniline) (POMA) or poly(2,5-dimethoxyaniline) (PDMA) in the presence of polystyrene(4-sulphonic acid) (PSSA). The Au/MBT/POMA-PSSA/AChE and Au/MBT/PDMA-PSSA/AChE biosensors were then applied to successfully detect standard organophosphorous and carbamate pesticides in a 0.1 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Secondly, it reports the construction of the Au/MBT/PANI/AChE/PVAc thick-film biosensor for the determination of certain organophosphate and carbamate pesticide solutions in selected aqueous organic solvent solutions. The Au/MBT/PANI/AChE/PVAc electrocatalytic biosensor device was constructed by encapsulating acetylcholinesterase (AChE) enzyme in the PANI polymer composite, followed by the coating of poly(vinyl acetate) (PVAc) on top to secure the biosensor film from falling off. The electroactive substrate called acetylthiocholine (ATCh) was also chosen to replace acetylcholine (ACh) as substrate, since ATCh has better redox activity and can both be oxidised and reduced to provide better movement of electrons in the amperometric biosensor. The voltammetric results have shown that the current shifts more anodically as the Au/MBT/PANI/AChE/PVAc biosensor responded to successive acetylthiocholine (ATCh) substrate addition under anaerobic conditions in 0.1 M phosphate buffer, KCl (pH 7.2) solution. For the Au/MBT/PANI/AChE/PVAc biosensor, various performance and stability parameters were evaluated. These factors include the optimal enzyme loading, effect of pH, long-term stability of the biosensor, temperature stability of the biosensor, the effect of polar organic solvents, and the effect of non-polar organic solvents on the amperometric behaviour of the biosensor. The Au/MBT/PANI/AChE/PVAc biosensor was then applied to detect a series of 5 organophosphorous and carbamate standard pesticide solutions. The organophosphorous pesticides studied were diazinon, fenthion, parathion-methyl, malathion and chlorpyrifos; while the carbamate pesticides included dioxacarb, aldicarb, carbaryl, carbofuran and methomyl. Very good detection limits were obtained for the standard pesticide solutions and they were within the nanomolar range. The detection limit values for the individual pesticides were 0.137 nM (diazinon), 0.826 nM (fenthion), 1.332 nM (parathion-methyl), 0.189 nM (malathion), 0.018 nM (chlorpyrifos), 1.572 nM (dioxacarb), 1.209 nM (aldicarb), 0.880 nM (carbaryl), 0.249 nM (carbofuran) and 0.111 nM (methomyl). The detection limit results showed that the thick-film Au/MBT/PANI/AChE/PVAc biosensor was more sensitive to organophosphorous and carbamate pesticides compared to other biosensor results found in the literature.