Core-shell nanoparticles as surface-enhanced raman scattering substrates for sensitive detection of thiram

Abstract

Plasmonic nanoparticles have been widely used as substrates in surface-enhanced Raman scattering (SERS) due to their unique optical properties known as localized surface plasmon resonance (LSPR). In recent years, these nanomaterials have attracted much attention for their applications in chemical sensing, biosensing and imaging. In this study, we have synthesized Au@Ag core-shell nanoparticles with 1,4-benzenedithiol (1,4-BDT) sandwiched in between the Au-Ag gap of the core-shell structure, where the Raman signal from the 1,4-BDT molecules were greatly enhanced. This gap- enhanced Raman scattering signal was then used as an internal reference Raman signal. For this structure, detailed parameters, such as the core size and shape, shell thickness, were studied and optimized. Our results showed that the Raman intensity of 1,4-BDT would first increase to a maximum with the increasement in the thickness of the silver shell, while further increasement in the shell thickness would cause the SERS intensity to drop. We have then optimized the Raman tagged Au@Ag core-shell structure to obtain a probe with a stable reference Raman signal. These probes were then used for the trace detection of the pesticide of thiram through SERS. Using the reference peaks from 1,4-BDT, quantitative measurements of thiram were obtained with good linearity and reproducibility. Furthermore, due to the enhancement of the SERS effect, our probes were able to detect the pesticide at a low level of ~10^-7 M at 559 cm^-1 . In addition, combining the optimized core-shell Au@Ag nanoparticles and other metallic nanostructures would further enhance the detection sensitivity. These results show that SERS based on Au@1,4-BDT@Ag nanostructures could be a promising tool for chemical trace analysis.