A label-free SERS probe for highly sensitive detection of Hg²⁺ based on functionalized Au@Ag nanoparticles

Unbiodegradable toxic Hg²⁺ accumulates in ecological systems and results in contaminated food chain, exposing us to high level pollution and healthy risk. Here, monolayer 2,5-Dimercapto-1,3,4-thiadiazole (DMcT) functionalized Au@Ag nanoparticles (NPs) were controllably constructed as a label-free SERS probe. Based on them, we can perform rapid and easy Hg²⁺ identification with high sensitivity and selectivity over competing analytes. Remarkably, DMcT acted as both interior label and target acquisition. Since DMcT showed intrinsic Raman signal when attached to substrates surface, it can be employed for quantification instead of extra conventional signal label. Also, we've demonstrated that DMcT coordinated on the surface of Au@Ag NPs as bidentate ligand with both the thiocarbonyl sulfur atoms while the nitrogen atoms on the different sides of the molecule were devoted to Hg²⁺ recognition. Owing to the strong coordination between Hg²⁺ and nitrogen atoms, as low as 10pM Hg²⁺ can be detected. The probe responded a good linear relationship ranging from 0.05 to 100nM and the limit of detection is ~3 orders of magnitude lower than the United States Environmental Protection Agency (USEPA)-defined limit (10nM) in drinkable water (EPA: Washington, DC, 2001). Furthermore, our suggested platform is highly effective to perform real samples detection. Utilizing the environmental water from East Lake, Wuhan, it resulted in better accuracy over the conventional standard method.