High-performance bimetallic thin film fiber optic SPR sensors: a new approach to analyte detection

Abstract Surface Plasmon Resonance (SPR) based sensors have attracted significant attention due to their sophisticated detection capabilities. The principle behind SPR sensors involves the excitation of surface plasmons, which are collective electron oscillations at the interface between a metal layer and a dielectric medium triggered by incident light. Among the various SPR sensor types, optical fiber-based SPR sensors stand out. This method channels light through an optical fiber, directing it onto a metal film coated on the fiber’s surface. Fiber optic SPR sensors offer numerous advantages over conventional prism-based SPR sensors, including miniaturization, simplified optical design, remote sensing, high sensitivity, and real-time analysis. To enhance the performance of fiber optic-based SPR sensors, this study investigated the impact of metal film material and thickness on the sensor’s spectral characteristics. We developed a D-shaped fiber-optic SPR sensor for detecting glycerin concentrations in solutions with varying refractive indices. Experiments showed that the sensor producing the most significant wavelength shift in SPR resonance while detecting glycerin utilized a bimetallic thin film of Ag/Au, with Ag at 31.8 nm and Au at 42.3 nm. By monitoring shifts in the SPR resonance peak wavelength, we determined the sensor’s performance parameters, revealing a sensitivity of 0.2489 ± 0.011 nm mM −1 within a glycerin concentration range of 0.05–0.48 mM. We have investigated the Langmuir, Freundlich, and Temkin isotherm models to determine the sensitivity and detection limits of surface plasmon resonance (SPR) responses in glycerin across a broad concentration range. We can elucidate how surface chemistry influences sensor performance by cross-validating the interactions between glycerin and bimetallic AgAu films. This comprehensive approach enables the accurate quantification of key parameters, such as binding affinity and adsorption capacity, which are essential for optimizing sensors for practical applications. With its simple structure and cost-effectiveness, this sensor presents a practical and promising tool for applications in biomarker detection, biochemical screening, and environmental monitoring, offering hope for future advancements in these fields.