Highly Sensitive U-Shaped Fiber Optic Surface Plasmon Resonance Biosensors Using Bi2O2Se and Au Nanoparticles Composite Nanomaterials for Biomedical Diagnostics

Composite nanomaterials significantly enhance sensor sensitivity in surface plasmon resonance (SPR) applications. This study presents a novel U-shaped multimode fiber-no-core fiber-multimode fiber (MMF-NCF-MMF) SPR sensor integrated with an Au film-Bi₂O₂Se&Au nanoparticles (AuNPs) composite system. Incorporating Bi₂O₂Se (an emerging 2D semiconductor with excellent optoelectronic properties) and AuNPs, the sensor leverages plasmon mode coupling between the Au film and AuNPs, plus the synergistic electron mobility regulation of Bi₂O₂Se&AuNPs, to boost refractive index (RI) sensitivity. The NCF reduces transmission loss and narrows the full width at half maximum (FWHM), enhancing target detection performance. At an MMF-NCF-MMF length ratio of 15mm:4mm:7mm, the composite-modified sensor achieves an RI sensitivity of 7552.31 nm/RIU—112.06% higher than the pure Au film sensor (3561.4 nm/RIU). It also exhibits a 14.3 nm FWHM reduction and a 1.24-fold figure of merit (FOM) increase (from 14.280 to 32.003), along with excellent temperature stability (RSD = 0.603%) and repeatability. For biomolecular validation, C-reactive protein (CRP)—a key clinical biomarker for inflammation and post-surgical infection—was targeted. The sensor shows reliable concentration-signal correlation (R² = 0.969) over 0.1–25 μg/mL, with a limit of detection (LOD = 3σ/S, IUPAC-recommended) optimized to 13.08 μg/mL at 1 μg/mL, aligning with clinical moderate inflammation ranges. By integrating SPR-localized surface plasmon resonance (LSPR) coupling and Bi₂O₂Se&AuNPs synergistic sensitization, this sensor holds substantial potential for clinical diagnosis and immunoassays.