Enhanced SPR Sensor Characteristics and Performance via TiO₂/CQDs Nanocomposite Functionalization of D-Shaped Fiber Optic SPR Sensor for Highly Sensitive Interleukin-17 Detection

• The incorporation of CQDs modified the morphology, microstructure, and optical properties of TiO₂, resulting in smaller particle size and a narrowed bandgap. • Bandgap narrowing increased the refractive index and enhanced SPR characteristics • Increasing the deposition time of TiO₂/CQDs via USP technique reduces the surface roughness and results in optimal transmittance. • TiO₂/CQDs modification enhanced the fiber-optic SPR sensor for IL detection, yielding a high sensitivity of 2095.08 nm/RIU High sensitivity is crucial for fiber-optic surface plasmon resonance biosensors. This study presents an enhanced Au-coated SPR sensor functionalized with a TiO₂/Carbon Quantum Dots (CQDs) nanocomposite thin film. The CQDs were sustainably synthesized from sugarcane bagasse using an eco-friendly hydrothermal method. By employing Ultrasonic Spray Pyrolysis, the TiO₂/CQDs nanocomposite optimizes both the plasmonic layer and the evanescent-field distribution. Sensor performance for the human IL-17 isolate showed significant improvements: sensitivity increased significantly from 2947.49 nm/RIU (single Au) to 4244.38 nm/RIU Au–TiO₂/CQDs, achieving a Figure of Merit (FOM) of 38.75 RIU⁻¹. This environmentally friendly approach promises highly sensitive SPR sensor development.