Tapered single-mode optical fiber-based on localized surface plasmon resonance as refractive index sensor

A simple tapered single-mode optical fiber-based on localized surface plasmon resonance was proposed as a refractometer for liquid samples application. The tapered optical fiber (TOF) was fabricated by using a flame-brush method and achieved a waist diameter of 16.5 mu m over the length about 20 mm. 3-mercatoptopropyltrimethoxysilane (MPTMS) with a mercapto group (-SH) was utilized as a silane agent to immobilized the nanoparticles by strong covalent bonding between sulphur and gold. The sensing mechanism relies on the transmission shifting in the output spectra due to the evanescent field absorption by immobilized gold nanoparticles on TOF surface. The performance of TOF has been evaluated with the surrounding refractive index varied over the range from 1.3330 to 1.4229. The sensitivity of the sensor was recorded at 18 nm/RIU with good repeatability and stability for 70 minutes.