Plasmonic-based nanogap structures play a key role in enhancing sensitivity in plasmonic applications. While nanogap width has often been shown to influence optical properties, controlling material composition at nanogap regions remains challenging. Using a templated synthesis approach, we fabricated Au@shell (Au, Ag, Pd, Pt) nanoparticle dimers with sub-10 nm gaps and controlled shell growth by tuning solution pH and reduction kinetics. We found that Au@Ag dimers exhibited significantly higher SERS signals compared to Au@Au dimers, while Au@Pd and Au@Pt dimers enabled real-time monitoring of catalytic reactions. We attribute these effects to the interplay between plasmonic enhancement and surface reactivity, which dictate molecular interactions within the nanogap. Our study highlights the potential of bimetallic nanoparticle dimers as multifunctional platforms for plasmon-based sensing and catalysis.
