SPR-Based Optical Fiber Sensors Using Gold–Silver Alloy Particles as the Active Sensing Material

A number of different gold–silver alloy particles, on a nanometre scale and ranging in size from 13 to 34 nm in diameter (nanoparticles), have been prepared and been investigated as the active elements of optical fiber sensor systems. This includes a gold-rich group with 25% silver and 75% gold (the A25 group) in content and a silver-rich group with 75% silver and 25% gold in content (the A75 group). Subsequently, the alloy nanoparticles that are synthesized are coated onto the surface of optical fibers to create surface plasmon resonance-based optical fiber sensors for refractive index measurement. The experimental results show that both the size of the alloys and the alloy content determine the sensitivity of the measurement probes created. In this paper reported, the A75 group sensors have demonstrated better performance than those of the A25 group, with similar particles sizes and a highest sensitivity of 611 nm/refractive index unit (RIU) being achieved with a sensor coated with A75 alloy with an average particle size of 34 nm.