Researchers have developed a novel optical biosensor that employs a hybrid plasmonic-photonic multi-Fano resonance for detecting changes in refractive index. This device integrates a microcavity with periodic gold nano-bars, achieving high sensitivity and a significantly improved figure of merit (FOM) compared to sensors based on simple Fano resonances or purely plasmonic designs. The key to its performance lies in the complex interaction between the photonic modes of the microcavity and the localized surface plasmons generated by the gold nano-bars.

The proposed design utilizes a microcavity structure coupled to a waveguide, upon which gold nano-bars are periodically deposited. This configuration allows for the simultaneous excitation of multiple Fano resonances, characterized by their distinct asymmetric profiles, which are highly sensitive to small variations in the surrounding medium's refractive index. The hybrid interaction between the confined photonic modes and the localized surface plasmons amplifies the optical response, facilitating the detection of biomolecules or chemical changes with unprecedented precision.

The obtained results demonstrate a figure of merit (FOM) of 1.12 × 10^4, a value that significantly surpasses typical conventional optical sensors. This improvement translates into an enhanced ability to discriminate between samples with very similar refractive indices, which is crucial for biomedical and chemical applications. The capability to generate multiple Fano resonances in a single device opens the door to multiplexing, allowing for the simultaneous detection of several analytes, which could revolutionize in vitro diagnostics and environmental monitoring.