For the first time it is demonstrated that sulfhydryl compounds can suppress longitudinal etching of gold nanorods via consuming oxidizers, which provides a new signaling mechanism for colorimetric sensing. As a proof of concept, a colorimetric assay is developed for detecting organophosphorus pesticides, which are most widely used in modern agriculture to improve food production but with high toxicity to animals and the ecological environment. Triazophos was selected as a model organophosphorus pesticide. In the absence of triazophos, the active acetylcholinesterase can catalyze the conversion of acetylthiocholine iodide to thiocholine whose thiol group can suppress the I2-induced etching of gold nanorods. When triazophos is present, the activity of AchE is inhibited, and I2-induced etching of gold nanorods results in triazophos concentration-dependent color change from brown to blue, pink, and red. The aspect ratio of gold nanorods reduced with gradually blue-shifted longitudinal absorption. There was a linear detection range from 0 to 117 nM (R2 = 0.9908), the detection limit was 4.69 nM, and a good application potential was demonstrated by the assay of real water samples. This method will not only contribute to public monitoring of organophosphorus pesticides but also has verified a new signaling mechanism which will open up a new path to develop colorimetric detection methods. It has been first found that sulfhydryl compounds can suppress longitudinal etching of gold nanorods (AuNRs) via consuming oxidizers, which provides a new signaling mechanism for colorimetric sensing. As a proof of concept, a colorimetric assay is developed for sensitively detecting organophosphorus pesticides (OPs). It will not only contribute to public monitoring of OPs but also has verified a new signaling mechanism which will open up a new path to develop multicolor colorimetric methods.
Keywords: Colorimetric assay; Gold nanorods; Iodine etching; Organophosphorus pesticides; Triazophos.