A dual - mode refractive index sensor based on multilayer gold nanodisk - intercalated UCNP heterogeneous metamaterial

• Dual-mode sensor integrates spectral shift and fluorescence enhancement detection. • Heterogeneous metamaterial enables multi-wavelength local field enhancement. • Linear field strength-refractive index correlation supports dual-mode sensing. • Broad compatibility with various doped UCNPs for diverse applications. • Glucose detection shows excellent dual-mode sensing performance. High-precision refractive index sensors are pivotal for medical diagnostics, environmental monitoring, and bioanalysis. This study presents a dual-mode refractive index sensor integrating spectral shift detection and fluorescence enhancement through a gold nanodisk-UCNP heterogeneous metamaterial. By optimizing structural parameters (e.g., metal layer number, nanodisk radius), tunable multiplexed band absorption is achieved. The platform exhibits strong local field amplification at 808, 980, 1064, and 1550 nm wavelengths, significantly boosting UCNP optical signals while accommodating diverse sensitizer doping configurations. Beyond conventional refractive-index-induced spectral shifts, a linear correlation between local field strength and refractive index is revealed, enabling a dual-mode mechanism that concurrently links spectral shifts and luminescence intensity to refractive index variations. Demonstrating broad compatibility with UCNP with different dopant ions, this design advances sensing technology through synergistic spectral-intensity modulation, with applications spanning diabetes detection, tunable nanolight sources, and high-sensitivity environmental monitoring systems.