A thermally and mechanically stabilized plasmonic optical fiber sensor for real-time biomarker monitoring

Abstract

Optical fiber sensors based on surface plasmon resonance (SPR) are powerful tools for biosensing, yet their performance is often hindered by thermal and mechanical instability. This work presents the design, fabrication, and characterization of an integrated optofluidic platform that overcomes these environmental limitations. A tilted fiber Bragg grating (TFBG) with an 11° tilt angle was coated with a numerically optimized bilayer of 5 nm chromium and 45 nm gold to achieve a strong plasmonic response. To ensure measurement reliability, the TFBG-SPR sensor was encapsulated within a PDMS microfluidic chip, which was mounted on a Peltier element for active thermal regulation. This system provides robust mechanical shielding and maintains a stable temperature of 27 °C with a precision of ±0.02 °C, effectively eliminating signal drift. A robust signal demodulation algorithm using Fourier filtering was implemented to accurately determine the SPR wavelength from the complex transmission spectrum. The sensor exhibited a sensitivity of 552 nm/RIU to refractive index changes. The platform's performance was validated by monitoring the real-time immobilization of bovine serum albumin, which resulted in a permanent wavelength shift of 1 nm. The successful integration of the plasmonic fiber sensor into a stabilized microfluidic environment demonstrates a reliable and highly sensitive "Lab-on-a-Fiber" system suitable for practical biosensing applications.