A Splice-Free Dual-Mode Optical Fiber Biosensor for Sensitive and Temperature-Compensated β-Actin Detection via SPR and MZI Integration

This study presents a novel optical fiber biosensor configured for the concurrent measurement of β-actin (ACTB) and temperature. This device is built upon a single-mode optical fiber platform and uses Fast Fourier Transform (FFT) for data processing. The device’s functionality is achieved by the synergistic integration of two distinct sensing principles: surface plasmon resonance (SPR) and Mach-Zehnder interferometry (MZI). By leveraging the specific binding between ACTB antigens and immobilized antibodies on the fiber surface, the refractive index (RI) changes upon complex formation, resulting in distinct spectral shifts in both SPR and MZI channels, thus enabling precise ACTB detection. Notably, this is the first reported design to realize the dual SPR–MZI sensing effects directly on a single, continuous optical fiber—without requiring fiber fusion or splicing—greatly simplifying the fabrication process. The dual-channel configuration also allows for effective temperature compensation. Experimental results demonstrate high RI sensitivities of 2230 nm/RIU for the SPR channel and 309 nm/RIU for the MZI channel, as well as temperature sensitivities of 0.43 nm/°C (SPR) and 0.208 nm/°C (MZI). The sensor exhibits a rapid response time of 200 seconds for ACTB detection, with a sensitivity of 6.5 nm/(ng/mL), a linear detection range of 0–5 ng/mL, and a limit of detection (LOD) as low as 0.0442 ng/mL. Additionally, a straightforward SPR dip modulation technique is introduced, whereby the SPR resonance position can be effectively tuned by adjusting the fiber’s bending angle. The use of a large-diameter taper not only enhances mechanical robustness but also maintains strong optical performance. Overall, this sensor offers high sensitivity, excellent stability, rapid response, and a low-cost, easy-to-manufacture structure.