Application of Porous TiO2 Thin Films as Wavelength-Interrogated Waveguide Resonance Sensors for Bio/Chemical Detection

Porous TiO 2 thin-film waveguides with the gold clad were fabricated by colloidal deposition for real-time detection of small molecule substances based on interrogating the guided mode resonance wavelength (λ R ). By measuring the reflected light intensity spectrum, both λ R and the sensor response were accurately obtained. The mode order corresponding to the detected λ R and the porosity of the TiO 2 film were determined by a combination of simulations and measurements. The sensor is responsive to nonspecific adsorptions of glutathione (GSH) molecules, lead(II) ions, and the block copolymer. The volume fraction ( f 3 ) of adsorbed GSH molecules was determined to be proportional to changes in λ R (Δλ R ). The saturation adsorption of GSH results in Δλ R = 8.1 nm, corresponding to f 3 = 0.085, that is 17.9% of the film porosity. The findings indicate that the adsorbed amount of GSH is equivalent to more than 10 complete monolayers with the same area as the porous TiO 2 film used. A quasi-linear dependence of Δλ R on the logarithm of the lead(II) concentration with the detection limit of 1 ppm was obtained for the sensor. The best fit to the time course of Δλ R measured with the sensor during the block copolymer adsorption process was obtained based on the Langmuir kinetics.