Ultrahigh-sensitivity D-shaped PCF-SPR biosensor with TiO2–Au hybrid layers for precise detection of blood constituents

Plasmonic biosensors based on photonic crystal fibers (PCF-SPR) have emerged as promising candidates for highly sensitive and real-time biomedical detection. In this study, we propose and numerically investigate a novel D-shaped PCF-based plasmonic biosensor incorporating a thin gold layer as the plasmonic medium and an optimized titanium dioxide (TiO₂) dielectric interlayer. This configuration significantly enhances light-metal interaction, improves mode confinement, and strengthens surface plasmon resonance (SPR) coupling efficiency. Three-dimensional finite element method (FEM) simulations are employed to examine the influence of critical design parameters, including the thicknesses of Au and TiO₂ layers, air-hole diameters and arrangement, and analyte refractive index (RI) variations, on resonance wavelength and confinement loss. The proposed sensor achieves an outstanding wavelength sensitivity (S_λ) of 14,000 nm/RIU, amplitude sensitivity (S_A) of 610 RIU⁻¹, and a resolution of 1.4 × 10⁻² RIU within the analyte RI range of 1.33–1.40. These performance metrics enable the discrimination of blood constituents such as water, plasma, hemoglobin, and red and white blood cells, even under conditions of closely matched refractive indices. The findings highlight the remarkable potential of PCF-SPR biosensors for rapid and precise blood analysis, offering new avenues for the advancement of next-generation biomedical diagnostic platforms.