Gold–silver nanoboxes: a systematic investigation of their SERS capability and dual functions

Surface-enhanced Raman spectroscopy (SERS) is a nondestructive technique that provides ultrasensitive, highly specific molecular structure information for trace analysis and multicomponent profiling in biosensing applications. SERS utilizes the ability of plasmonic nanostructures to enhance the electric field around their surface. Gold-silver nanoboxes (NBs) hold the promise of superior SERS-related performance compared to conventional spherical nanoparticles in part because of their readily accessible “hotspot” corners. In this study, three types of NBs were synthesized using a one-pot method and then characterized using various analytical techniques, including ultraviolet-visible spectroscopy, electron microscopy, and Raman spectroscopy. Our studies, which involved SERS detection under three laser excitations at 532, 633, and 785 nm and finite-element method simulations, revealed that NBs with a size of 75 nm displayed the highest SERS performance, compared to other synthesized NBs and spherical gold and silver nanoparticles. When the 75 nm NBs were functionalized with an Raman active molecule and coated with a fluorescein isothiocyanate dye-integrated silica shell, the NBs can be analyzed using both fluorescence and SERS, which promises their potential for sensitive and specific biosensing applications in the future.