Engineered of Bimetallic Au@Ag Nanostars with Controllable Branching and Tunable LSPR for Rapid Ultrasensitive SERS Detection

In this work, Au@Ag nanostars were successfully synthesized via a seed-mediated growth method, using presynthesized Au nanostars as structural templates. The structure of the Au@Ag nanostars can be precisely controlled by adjusting the concentration of AgNO3 and Au nanostar seeds. The structural configuration of the Au@Ag nanostars can be precisely tuned from partially encapsulated cores to fully encapsulated architectures. The Au@Ag nanostars display tunable localized surface plasmon resonance (LSPR) characteristics in response to changes in the Ag shell thickness. The Raman enhancement of 4-ATP indicates that surface-enhanced Raman spectroscopy (SERS) performs optimally when Ag fully encapsulate the Au nanostars, confirming the results from FDTD theoretical simulations. The remarkable sensitivity of SERS detection originates from the enhanced electromagnetic fields generated at both the nanogaps and branched ends of the Au@Ag nanostars, coupled with their optimized LSPR characteristics. The detection limit achieved an exceptionally low level of 10–15 M. Effective detection of pesticides such as thiram and carbaryl was also achieved. The structural configuration of the Au@Ag nanostars fully leverages the synergistic effects between Au and Ag, along with the nanogaps, to significantly enhance the sensitivity and stability of SERS detection. This study provides theoretical and experimental references for plasma metal nanostars with significantly enhanced electromagnetic fields and offers insights for future SERS studies.