LSPR based optical fiber sensors treated with nanosecond laser irradiation for refractive index sensing

Abstract This article reports on the application of localized surface plasmon resonance (LSPR) based optical fiber probes in the form of U-shape geometry, as refraction index (RI) sensors in sucrose and alcohol solutions. For their fabrication, the immobilization of gold nanoparticles (AuNP) on the probe’s active area was achieved by a dip-coating procedure and the formed AuNP decoration was tailored by ns laser irradiation at 532 nm. The procedure was monitored and controlled in real time by recording the induced changes into the optical fiber extinction spectra. For the optimization of the fabrication technique, an irradiation protocol is established while the dependence of RI sensitivity on the AuNP size and their abundance on the fiber have been explored. Sensors with RI sensitivities, comparable to the best reported in the literature (up to ΔE/ΔRI = 45.2) were developed from mono-dispersed colloidal solutions of AuNP. Finally, it should be stressed that following the same procedure, sensors with similar RI sensitivity (ΔE/ΔRI = 33.9) were fabricated by using a mixture of different size (20–100 nm) AuNP bypassing the necessity of mono-dispersed solutions.