Exploring the charge transfer enhancement mechanism in selective SERS detection with Mo_1-xW_xS₂@Ag₂S nanosheets

In order to solve the problem of poor sensitivity and selectivity of conventional SERS substrates, we synthesized Mo_1-xW_xS₂@Ag₂S nanosheets in this paper by a two-step hydrothermal method. The structure and morphology of the synthesized Mo_1-xW_xS₂@Ag₂S nanosheets were characterized by XRD and SEM,respectively. The results show that the Mo_1-xW_xS₂@Ag₂S nanosheet has an irregular layered structure. Further, the SERS properties of Mo_1-xW_xS₂@Ag₂S nanosheets were tested by using rhodamine 6G (R6G), crystalline violet (CV), and 4-mercaptobenzoic acid (4-MBA) as probe molecules, respectively. The test results demonstrated that the nanosheets were specific to R6G and CV probe molecules, and the mechanism of selectivity was due to CT enhancement. In addition, Mo_1-xW_xS₂@Ag₂S exhibits ultrahigh sensitivity in R6G and CV, with the corresponding detection limit of both reached 10^-8 M. And linear fitting of the peak intensities was carried out, with the R² coefficient of 0.981 and 0.951, respectively. Finally, the relative standard deviations (RSDs) of this Mo1-xWxS2@Ag2S nanosheets was obtained to be 8.56 % by test 1 × 10^-4 M R6G at the characteristic peak 613 cm^-1, which represents excellent detection repeatability. The Mo_1-xW_xS₂@Ag₂S nanosheets are rich in edge-active sites favorable for charge transfer, which can enhance the SERS signals of the target molecules better. Besides, the Raman detection of the surface of Mo_1-xW_xS₂@Ag₂S nanosheets using nitrofurantoin (NFT) also reached a detection limit of 10^-8 M. Mo_1-xW_xS₂@Ag₂S nanosheets substrates can find applications in medicine and provide new strategies for improving the SERS performance.