A New Strategy for Direct Electrochemical Sensing of a Organophosphorus Pesticide, Triazophos, Using a Coomassie Brilliant-Blue Dye Surface-Confined Carbon-Black-Nanoparticle-Modified Electrode

Triazophos, O,O-diethyl O-(1-phenyl-1H-1,2,4-triazol-3-yl)phosphorothioate (TPZ), an organophosphorus pesticide, has been widely used in agriculture to control pests, insects, and some nematodes (roundworms). Unfortunately, it has been found that a significant trace of the pesticide residue enters into the agricultural products and creates a major health threat to human. In order to selectively detect the TZP pesticide in real samples, several indirect and time-consuming analytical assays based on acetylcholinesterase enzymes, affinity-based antibody systems, and molecularly imprinted polymers, apart from the separation-coupled mass spectrophotometer, have been demonstrated. For the first time in the literature, we report a direct electrochemical method for the selective and quick detection of TZP based on electrocatalytic oxidation by a Coomassie brilliant-blue dye surface-confined carbon-black-nanoparticle-modified glassy carbon electrode (GCE/CBnano@CoomBB) in a pH 7 phosphate buffer solution. GCE/CBnano@CoomBB showed a stable and highly redox-active peak at E°′ = 0.15 V versus Ag/AgCl suitable for selective mediation of the TZP oxidation reaction. The quinonoid form of CoomBB and its strong π–π interaction with CBnano are found to be key parameters for the electrochemical TZP oxidation. Initially, amperometric i–t sensing at an applied potential, 0.1 V versus Ag/AgCl, was demonstrated for the highly selective detection of TZP without any interference from common chemicals like uric acid, ascorbic acid, cysteine, nitrite, hydrazine, sulfide, citric acid, and hydrogen peroxide and other pesticides like cypermythrin, propenofos, deltramethrin, parathion, and monocrotophous. Further, this new electrochemical system was exploited to flow-injection analysis of TZP with a working volume of 20 μL. The calibration plot is linear in a window of TZP concentration of 16–632 ng/20 μL with a detection limit value of 119 pg/20 μL. Application of this technique is further demonstrated by detecting the TZP content in a couple of simulated vegetable samples with appreciable recovery values.