Gold nanoclusters-based dual-mode ratiometric sensing system for selective and sensitive detection of paraquat.

Unreasonable or illegal utilization of pesticides may lead to pollution of agricultural products, especially with some persistent but effective pesticides. Hence, there is an urgent need to develop sensitive and rapid methods for pesticide detection to ensure the safety of agricultural products. Herein, a dual-mode ratiometric sensing system utilizing two gold nanoclusters (G/R-AuNCs) was designed and constructed for paraquat (PQ) detection, a typical, highly toxic, widely used pesticide. Initially, a ratiometric fluorescent method was developed based on green-emitting (Em∼530 nm) and red-emitting (Em∼655 nm) gold nanoclusters. Relying on the electrostatic interaction between G-AuNCs and PQ, G-AuNCs were quenched as a sensing unit. R-AuNCs with chemical inertness and excellent stability to PQ served as correction signals. The selective and sensitive detection of PQ was successfully achieved with a satisfactory linear relationship within the range of 5-500 μg/L, and the limit of detection (LOD) was as low as 1.68 μg/L (6.5 nM). Furthermore, PQ can be detected through visual analysis based on smart mobile devices. As the concentration increased, a more noticeable color change occurred, producing a significant shift from yellow to red under 365 nm UV light, resulting in a striking visual effect. This research not only showcases the practical benefits of the dual-mode analytical method but also drives forward the application of ratiometric probes.