Manipulating Fano Resonance Using Notch Nanogap Nanoantenna for SERS Detection

Noble metal nanostructures have attracted substantial interest due to their unique optical properties, particularly their localized surface plasmon resonance (LSPR), which enables significant near-field electromagnetic enhancements. Among these, bowtie nanoantennas (BNAs) stand out for their strong plasmonic coupling at nanogap regions, making them highly effective in applications such as surface-enhanced Raman scattering (SERS). However, the limited hotspot area and potential scattering losses at peak enhancement wavelengths remain challenges for practical applications. To address these limitations, we designed and investigated a notch metal–insulator–metal bowtie nanoantenna (MIM-BNA) structure. Ge materials were horizontally integrated into conventional Ag-BNA nanostructures, and notched silver nanorods were strategically placed in the nanogap region to disrupt the geometric symmetry, thereby inducing Fano resonance. This approach successfully coupled bright (dipole mode of the nanorod array) and dark plasmonic modes (antisymmetric mode of the MIM-BNA), enhancing the electric field at the Fano dip wavelength. Further analysis explored the effects of material composition, stacking configurations, and nanorod arrays on near-field enhancement. Our findings demonstrate that the MIM-BNA structure significantly improves the near-field effect, provides more flexible adjustment of the operating wavelength within the visible and near-infrared (NIR) light spectrum, and expands the hotspot area compared to traditional BNAs, providing a promising platform for advanced SERS applications and other plasmonic technologies.