A SERS “on–off” sensor for Hg2+ and fumonisin B1 determination in grains based on Au-Janus Ag NPs modified by carbon dots

Se-WCDs-Au-Janus Ag NPs with weak oxidase activity were synthesized using Se-W carbon dots (Se-WCDs) as stabilizers and reducing agents. These Janus nanoparticles (Janus NPs) effectively catalyze the reduction of mercury ions (Hg 2+ ) to metallic mercury (Hg 0 ), generating Au–Ag-Hg mercury alloys (Au–Ag@HgNPs). The aggregated Au–Ag@HgNPs on the nanoparticles improve the SERS activity of Se-WCDs-Au-Janus Ag NPs through a synergistic effect of electromagnetic enhancement and chemical enhancement. Interestingly, adding FB1 turns off the Raman signal by inhibiting the aggregation of Au–Ag@HgNPs. Based on these findings, a SERS “on–off” sensor utilizing the Se-WCDs-Au-Janus Ag NPs as the probe was successfully developed to determine fumonisin B1 (FB1) and Hg 2+ in grains. The detection limits were as low as 0.005 μg·L −1 for Hg 2+ and 0.006 μg·L −1 for FB1. Graphical abstract