Microchip enzymatic assay of organophosphate nerve agents

An on-chip enzymatic assay for screening organophosphate (OP) nerve agents, based on a pre-column reaction of organophosphorus hydrolase (OPH), electrophoretic separation of the phosphonic acid products, and their contactless-conductivity detection, is described. Factors affecting the enzymatic reaction, the separation and detection processes have been assessed and optimized. The complete bioassay requires 1 min of the OPH reaction, along with 1–2 min for the separation and detection of the reaction products. The response is linear, with detection limits of 5 and 3 mg/l for paraoxon and methyl parathion, respectively. Compared to conventional OPH-based biosensors, the OPH-biochip can differentiate between the individual OP substrates. The attractive behavior of the new OPH-based biochip indicates great promise for field screening of OP pesticides and nerve agents. The study demonstrates also for the first time the suitability of the contactless-conductivity detection for on-chip monitoring of enzymatic reactions.