Unmodified screen-printed silver electrode for facile detection of organophosphorus pesticide

An uncomplicated method for the detection of organophosphorous pesticide characterized by a thione moiety (P = S) was developed, and chlorpyrifos was used as an example. It was based on the detection of thiocholine generated by acetylcholinesterase. Organophosphorothionates slightly inhibited acetylcholinesterase, and P = S in chlorpyrifos was oxidized into P = O to improve the toxicity. Optimized amount of n-bromosuccinimide (4 ppm) and ascorbic acid (20 ppm) were used for the conversion. The influence of the excessive ascorbic acid and the high overpotential of the thiocholine was addressed by using a screen-printed silver electrode. According to cyclic voltammetry and amperometry, oxidization of thiocholine occurred on the electrode at a low potential while the ascorbic acid was not oxidized. The working potential was minimized to 0 V, and a detection limit of 2.5 ppb for chlorpyrifos was obtained. This method was further used to detect chlorpyrifos in Fuji apple and cucumber.