Design and simulation of a high sensitivity 2D photonic crystal waveguide biosensor for vitiligo detection

In this work, we present a high-performance Optical biosensor for the non-invasive detection of vitiligo, a skin disorder characterized by depigmentation resulting from melanin loss.. The sensor is designed on a two-dimensional (2D) Photonic Crystal (PhC) slab fabricated on a silicon-on-insulator (SOI) platform with a triangular lattice of air holes. The proposed design incorporates an input bus waveguide, a circular ring cavity, a hexagonal centre ring, a triangular ring, and an output drop waveguide to achieve strong resonance coupling and field confinement. The biosensor operates by monitoring refractive index variations of the skin analyte, which correlate with changes in melanin and keratin concentration. Resonant wavelength shifts are used to quantify these variations, enabling accurate identification of vitiligo-related anomalies.This sensor exhibits high-performance specifications, with a maximum quality factor of 16,388 for keratin-related conditions, a minimum spectral line width of 0.1 nm for all conditions, and a maximum sensitivity of 175 nm/RIU for melanin-related conditions. The device has a compact footprint of 97.52 µm 2 makes it suitable for on-chip biomedical integration. Unlike conventional PhC biosensors that restrict analyte infiltration to limited regions, this device is designed to fill the entire PhC structure with the analyte, rather than confining it to a specific region of the structure, which helps increase the reliability and repeatability of measurements. The sensor offers a promising platform for non-invasive and accurate detection of vitiligo.