“Light Up” Fluorescence Visual Sensitive Detection of Organophosphorus with a Smartphone-Based Platform Utilizing a Composite Rhodamine B-Ag@Au Nanoprobe

The present work reports a fluorescent sensor by utilizing a composite Rhodamine B-Ag@Au nanoprobe for the visual and semi-quantitative assay of organophosphorus pesticide (OP) residues via a “light up” sensing phenomenon. Core–shell structured Ag@Au NPs can directly quench the orange fluorescence of Rhodamine B (RB) at 580 nm based on Förster resonance energy transfer. Due to the stronger coordination ability of Ag@Au NPs with OPs, OP residues can displace RB from the surface of Ag@Au NP; thus, the RB fluorescence can effectively recover. Under optimum conditions, the composite fluorescent nanoprobe shows sensitive responses to OP residues in the range of 0.001–0.4 μM with a sensitive detection limit (LOD) of 7.89 nM. Moreover, combined with the smartphone color recognizer application (APP), the ratio of fluorescence intensity response is recorded on the green channel (G)/red channel (R), which has been employed for visual quantitative determination of OPs with an LOD of 16.3 nM. This proposed light up fluorescent sensor is also applied to OP residue identification in real water and agricultural samples with highly promising performance. The method reported here provides a convenient pathway for rapid and visual detection of pesticide residues utilizing organic composite nanomaterials.