Colorimetric detection of paraquat in aqueous and fruit juice samples based on functionalized gold nanoparticles

Paraquat (PQ) is a kind of herbicide, which is highly toxic to human body. In this work, we proposed a fast and simple detection method for PQ in aqueous samples based on electrostatic interactions between modified gold nanoparticles (Au NPs) and PQ. Au NPs were first modified with sodium 3-mercapto-1-propanesulfonate (Au NPs-3MPS). 3MPS with negative charge can interact with nitrogen atoms of PQ with positive charge via electrostatic force. As a result, Au NPs-3MPS aggregated together. Accordingly, the color of Au NPs-3MPS colloid changed from red to blue-gray, and the UV–vis absorption spectrum changed accordingly. The detection limit of PQ is 0.1 mg/L by naked eyes, and 0.001 mg/L by UV–vis spectroscopy. Moreover, this detection method has good specific selectivity and anti-interference performance, and it has been successfully used for detecting PQ in real environmental samples and fruit juice samples.