This work presents a compact, CMOS-compatible, Fano-engineered Nested Ring Resonator (NRR) for advanced biosensing applications. The proposed design supports three distinct Fano resonances within a single device, each exhibiting sharp spectral asymmetries that enhance sensitivity to refractive index variations. The device demonstrates an extinction ratio exceeding 50 dB, a spectral contrast of 99.95 \(\%\) , a quality factor ( \(Q\) ) of 7192, a maximum sensitivity of 583.3 nm/RIU and FOM of 1587 RIU-1, significantly outperforming conventional Lorentzian-based resonators. The novelty of the approach lies in achieving high-contrast, high- \(Q\) Fano resonances through a minimal structural modification in NRR without requiring complex or large-scale architectures. The device allows simultaneous multi-analyte detection, facilitated by distinct Fano resonances at different wavelengths, for analyte refractive indices in the range of 1.33–1.50 RIU. The Fano parameter ( \(q\) ) extracted through lineshape fitting exhibits considerable tunability, further broadening the device applicability. These results highlight the potential of Fano-engineered NRRs as practical, scalable, and integrable platforms for next-generation lab-on-chip photonic biosensing systems.
