Facile synthesis of intra-nanogap enhanced Raman tags with different shapes.

Hot spot engineering in plasmonic nanostructures plays a significant role in surface enhanced Raman scattering for bioanalysis and cell imaging. However, creating stable, reproducible, and strong SERS signals remains challenging due to the potential interference from surrounding chemicals and locating SERS-active analytes into hot-spot regions. Herein, we developed a straightforward approach to synthesize intra-gap nanoparticles encapsulating 4-nitrobenzenethiol (4-NBT) as a reporter molecule within these gaps to avoid outside interference. We made three kinds of intra-gap nanoparticles using nanorods, bipyramids, and nanospheres as cores, in which the nanorod based intra-gap nanoparticles exhibit the highest SERS activity. The advantage of our method is the ease of preparation of high-yield and stable intra-gap nanoparticles characterized by a short incubation time (10 mins) with 4-NBT and quick synthesis without requiring an additional step to centrifuge for the purification of core nanoparticles. The intense localized field in the synthesized hot spots of these plasmonic gap nanostructures holds great promise as a SERS substrate for a broad range of quantitative optical applications.