Dual-mode optical fiber sensor with polydopamine-functionalized surface and PDMS-enhanced temperature compensation for ultrasensitive HCG detection

This study introduces a temperature-compensated dual-mode optical fiber sensor for ultrasensitive human chorionic gonadotropin (HCG) detection, integrating polydopamine (PDA) nanostructures with polydimethylsiloxane (PDMS)-modified microcavities. The hybrid design synergistically enhances surface plasmon resonance (SPR) and Fabry-Pérot (FP) responses through engineered material interfaces. PDA enables efficient antibody immobilization via amine coupling, while PDMS simultaneously acts as a thermal expansion compensator and optical phase modulator, overcoming temperature-induced signal drift in conventional biosensors. The system demonstrates dual refractive index sensitivity (1875 nm/RIU) and differentiated temperature responses (-0.12 nm/ °C SPR vs. -0.61 nm/ °C FP), enabling environmental decoupling through matrix analysis. The sensor achieves record HCG detection performance with 1.54 nm/(mIU/mL) sensitivity and 0.01 mIU/mL detection limit. This materials-driven approach merges functional polymer engineering with photonic design, establishing a new paradigm for field-deployable lab-on-fiber biosensors. The work advances multiplexed optical sensing technologies for point-of-care diagnostics and smart medical materials development.