Synergistic U-bent geometry and bimetallic plasmonics for ultra-sensitive fibre-optic SPR biosensing of cervical cancer.

Cervical cancer arises from uncontrolled proliferation of epithelial cells in the lower uterine cervix, primarily triggered by persistent infection with high-risk human papillomavirus strains. Timely and reliable detection of malignant cellular transformations is therefore essential for effective therapeutic intervention. Here, we report a highly sensitive plasmonic U-bent fibre-optic biosensor (FOB) integrated with Au and Ag nanocoatings for rapid identification of cervical cancer cells. This work is innovative in combining a U-bent fibre geometry, which enables robust waveguide propagation at a small bend radius (1-1.5 mm), with a bimetallic (Au-Ag) plasmonic interface, thereby significantly enhancing light-matter interaction and SPR sensitivity compared with conventional straight single and multi mode fibre sensors. The U-bent geometry markedly strengthens the interaction between leaky evanescent waveguide fields with the surrounding analyte, enabling enhanced plasmonic coupling compared with conventional straight fibre configurations. Detailed numerical simulations were employed to optimize critical structural parameters, including bend diameter, metallic layer thickness, and sensing length with different cancerous cells, resulting in substantial performance enhancement. Furthermore, the systematic optimization framework presented here provides a scalable pathway for translating high-performance FOBs from laboratory research to practical point-of-care (PoC) diagnostic platforms. The optimized sensor exhibits a maximum sensitivity of ∼34 050 nm RIU-1 in the RI range of 1.42-1.43, while maintaining sensitivities of approximately 22 000 nm RIU-1 across most of the investigated RI range. In addition to sensitivity, the resonance linewidth was assessed through a full width at half maximum (FWHM) of ∼77.5 nm, resulting in a figure of merit (FOM) of ∼25-30 RIU-1 and a limit of detection (LOD) of ∼1.3124 × 10-3 RIU. This plasmonic fibre architecture provides a robust and scalable platform for high-precision optical diagnostics and exhibits strong potential for clinical translation. Moreover, the proposed design is compatible with laboratory-scale fabrication and industrial production, supporting PoC deployment.