Manufacturing and optimization of sol-gel-based TiO2-SiO2 thin films as high refractive index overlays for long period grating-based biosensing

The manufacturing procedure and the optimization of high refractive index overlays for long period grating-based sensors are reported. The overlay consists of a sol-gel-based TiO2-SiO2 thin film. By carefully tuning the overlay thickness and refractive index, it is possible to bring the LPG in the so-called transition mode working region, and to optimize and maximize the LPG sensing performances. LPGs are here characterized as optical refractometers, and, after a suitable functionalization of the sol-gel coated fiber surface, as biosensors performing an IgG/anti-IgG bioassay.