Controlled Growth of Gold Nanobipyramids Using Thiocholine for Plasmonic Colorimetric Detection of Organophosphorus Pesticides

Implementing suitable additives as morphology control agents to tune the shape of gold nanocrystals is a great challenge, as it requires the production of additives in a controlled manner and subsequent rational design of its applications. Herein, thiocholine-controllable regulation of the shape of gold nanobipyramids (AuNBPs) is proposed for the first time. Subsequently, it is used for constructing a plasmonic colorimetric sensor for the detection of organophosphorus pesticides (OPs). The principle of the platform is that first, highly uniform AuNBPs are prepared in situ by a seed-mediated growth method. Then, the thiocholine produced from the hydrolysis of acetylthiocholine by acetylcholinesterase (AChE) can be selectively adsorbed on the surface of the gold seeds, preventing the gold seeds from forming AuNBPs. Transmission electron microscopy shows the evolution of the shape of AuNBPs from bipyramid to cube and finally irregular sphere as the concentration of thiocholine increases. Therefore, the AChE concentration is highly correlated with the shape of the grown gold nanoparticles. Consequently, a plasmonic colorimetric method is established for the sensitive detection of OPs with the ability to irreversibly inhibit AChE activity. The proposed method achieves highly sensitive detection of paraoxon and demeton with limit of detections as low as 1.07 and 6.48 ng mL–1, respectively. Owing to the advantages of simple operation and high sensitivity, this method has great potential in the monitoring of OPs in agricultural products.