Extremely sensitive multi-order mode refractive index sensor using TiO2 nanograss film and weakly bounded waveguide modes.

An extremely sensitive multi-order mode refractive index (RI) sensor was fabricated by coupling titanium dioxide nanograss film coated FTO conductive glass with Kretschmann prism. Both calculation and experimental studies were carried out. Theoretical analysis by employing resonant waveguide modes indicated that the maximum sensitivity could be achieved when the mode worked at the weakly-bounded condition. The experimental results showed that for p-polarized and s-polarized light, the sensor exhibited a maximum RI sensitivity of 2938.21 nm/RI unit (RIU) and 1484.39 nm/RIU in the 1st order mode, respectively. Its maximum figure of merit was as high as 77.77. The proposed sensor is promising to be applied in environmental monitoring, immune analysis, nucleic acid test, etc.