The integration of two-dimensional graphene with gold nanostructures has significantly advanced surface plasmon resonance (SPR)-based optical biosensors, due to graphene’s exceptional optical, electronic, and surface properties. This review examines recent developments in graphene-based hybrid nanomaterials designed to enhance SPR sensor performance. The synergistic combination of graphene and other functional materials enables superior plasmonic sensitivity, improves biomolecular interaction, and enhances signal transduction. Key focus areas include the fundamental principle of graphene-enhanced SPR, the functional advantages of graphene hybrid platforms, and their recent applications in detecting biomolecules, disease biomarkers, and pathogens. Finally, current limitations and potential future perspectives are discussed, highlighting the transformative potential of these hybrid nanomaterials in next-generation optical biosensing

Electrically tunable graphene metasurfaces commonly rely on Fermi-level modulation to reshape plasmonic resonances, a process that inherently couples amplitude control to undesirable resonance-frequency shifts. This work introduces a mechanism to bypass this trade-off: field-programmed second-harmonic generation (SHG) within a spectrally stable graphene–GaN terahertz nanocavity. By applying a vertical DC field, we activate an effective second-order nonlinear response at the graphene–GaN interface through electric-field-induced second-harmonic generation. Crucially, the cavity-backed hybrid mode remains nearly invariant under bias, effectively decoupling the nonlinear source modulation from resonance-frequency tuning. Full-wave nonlinear simulations confirm electrically programmable SHG emission with minimal resonance pulling, stable near-field profiles, and multi-resonant SH spectra. This platform, leveraging multi-resonant enhancement from hybrid cavity-plasmon modes, provides a robust architecture for spectrally stable, active nonlinear terahertz metasurfaces.