Simultaneous Detection of Carbamates and Organophosphate Pesticides at Bare Boron-Doped Diamond Electrodes

Abstract

Carbamate and organophosphate compounds are widely used pesticides because of their high insecticidal activity, and sometimes as nerve agents because of their crippling inhibition of the enzyme acetylcholinesterase (AChE)1. These compounds accumulate in the food chain and can hijack the nervous system of the target organisms indiscriminately. Traditional electrochemical methods of pesticide detection rely on layered structures atop noble metal or carbon electrodes to assist the loading of AChE, which produces currents proportional to its inhibition level. One of the clear advantages of boron-doped diamond (BDD) as an electrode material is its greater potential window in aqueous solutions, compared to conventional electrode materials2. This allows redox behaviour at extended potentials to be observed without damage to the electrode. Cyclic, differential-pulse, and square-wave voltammetric techniques were used to probe carbaryl (CB), carbofuran (CF), and malathion in Carmody buffers of pH 2–12. Oxidation of CF occurred at the three overpotentials 1.31 V, 1.44 V, and 1.69 V, and a broad reduction peak was observed at 1.10 V, referred against Ag|AgCl. Compared with the oxidation of CB at 1.35 V, these electrochemical differences allowed for simultaneous detection of both compounds. This non-enzymatic sensor demonstrated a linear calibration over a concentration range of 1–100 µM for CB (R=0.9834) and CF (R=0.9938). After exposure to 1 mM malathion, a reduction peak appears that is highly sensitive to pH, attributed to a complex carbon–oxygen adsorbate that is robust to aggressive cleaning methods and only removable by hydrogen plasma etching. This malathion modified surface may be advantageous in future applications such as pH sensing. The oxidised BDD demonstrated failsafe reproducibility, a linear response, and low detection limits at medically relevant concentrations. References Kostelnik, P. Kopel, A. Cegan, M. Pohanka, Sensors, 17 (2017) 676.V. Macpherson, Phys. Chem. Chem. Phys., 17 (2015) 2935-2949.