A U-Shaped Coreless Fibre Architecture for High Sensitivity Immunosensing of Staphylococcus Aureus

Staphylococcus Aureus is a leading pathogenic bacterium associated with a wide spectrum of hospital and community acquired infections. Rapid, sensitive detection of this pathogen is of paramount importance. Herein, we report a label-free optical fibre biosensor built using a single-mode-coreless fibre with a U-shaped tapered architecture for S. aureus detection. Enhanced evanescent field interaction resulting from the contrast of fibre tapering and U-bend geometry is used to achieve high refractive index sensitivity of up to 2565 nm/RIU. Different waist diameter fibres were fabricated and comprehensively characterised, with the 9μm waist showing the best sensitivity. Targeted bacterial detection is achieved through selective bacterial recognition using a porcine immunoglobulin (Ig)G antibody functionalised fibre surface via silanisation and carbodiimide coupling chemistry. The functionalised sensor shows stable optical performance in phosphate buffered saline and distinct; concentration dependent wavelength shifts up to 0.9 nm for 2460 CFU/mL S. Aureus detection range. Signal amplification by nanobead conjugation further improved the sensitivity ~2 × of the biosensor at lower bacterial concentrations. The sensor offers a compact, robust, and highly sensitive platform for rapid point-of-care biosensing applications.