A simple, label-free AuNPs-based colorimetric ultrasensitive detection of nerve agents and highly toxic organophosphate pesticide.

Here, a simple label-free colorimetric sensing method for organophosphate (OP) nerve agents and pesticide based on catalytic reaction of acetylcholine esterase (AChE) and the aggregation of lipoic acid (LA) capped AuNPs has been established, which is highly sensitive with a limit of detection (LOD) lowered to pM level. In this method, only the AChE hydrolysis product of acetylthiocholine (ATCh), i.e., cationic thiocholine (TCh) can induce the aggregation of LA capped AuNPs along with a distinct color change from red to steel-blue. When OPs as enzyme inhibitors exist, the generation of TCh can be suppressed and the color change of LA capped AuNPs is gradually diminished according to different concentrations of OPs. The feasibility of this method has been demonstrated by sensitive measurement of OP nerve agents and pesticide in a spiked fruit sample with reliable results. This distinct and rapid colorimetric response enables us to readily probe OPs without more technical demand.