High‐Quality Plasmonic Ag─Au Bilayer Nanobump Grating Sensor

A novel plasmonic sensing platform based on bimetallic silver–gold nanobump grating fabricated via a single‐step direct laser writing process is presented. The plasmonic modes excited at the surface of the grating are sensitive to the local refractive index and its changes, resulting in a spectral shift of the resonant peak. Comprehensive optical measurements reveal a linear redshift of the resonance with increasing refractive index, achieving a sensitivity of up to 933 nm/RIU and a figure of merit of up to 57 RIU −1 . The choice in resonant peak and optimization in operating conditions, such as the angle of incidence, allow us to achieve these values by enhancing plasmon coupling efficiency and reducing the resonance linewidth. The suggested method offers a free‐form design for the platform, maintaining high‐quality resonances while exhibiting great stability, repeatability, and durability.