Performance evaluation of defect-modified Nano-photonic structure for enhanced Bloch surface wave based biosensor

Non-invasive glucose monitoring has emerged as a crucial requirement for early diagnosis and continuous management of diabetes mellitus. One-dimensional photonic crystals (1D-PhC) that support Bloch surface waves have emerged as an alternative platform for label-free biosensing due to their low optical losses and strong surface-field confinement. In this research work, a defect-engineered photonic structure is optimized and proposed for detecting glucose in urine samples. The structure consists of a periodic dielectric stack with alternating high-index TiO₂ and low-index SiO₂ layers. The dispersion characteristics are modified by introducing a low-index SiO₂ surface defect layer. The sensor operation is numerically analyzed using angular interrogation at a wavelength of 632.8 nm. The impact of defect-layer thickness on resonance angle, linewidth and sensitivity is systematically investigated. Furthermore, the optimized structure is employed for refractive-index-based detection of glucose in urine. The analytical results show that the photonic structure optimized with N = 5 and a defect thickness of 200 nm exhibits strong localized electric-field resonance at the analyte interface. The proposed sensor achieves a refractive-index sensitivity of 68.62°/RIU, a narrow average linewidth of 0.00836° FWHM, a high figure of merit of approximately 8208 RIU −1 and a refractive-index limit of detection of 4.37 × 10 −5 RIU. The corresponding glucose-concentration LOD is approximately 30 mg/dL, enabling clinically relevant detection of urine glucose variation from 0 to 2000 mg/dL.