An interferometric biosensor composed of a prism-chamber assembly and a composite waveguide with a Ta2O5 nanometric layer

A highly sensitive integrated polarimetric interferometer biosensor with improved long-time stability and simple operation was prepared by using a novel prism-chamber assembly and an inexpensive waveguide made by sputtering a tapered nanometric layer of Ta2O5 on a single-mode glass waveguide. By comparing the measured refractive-index (RI) sensitivities with those simulated based on a four-layer homogeneous waveguide, both the equivalent thicknesses (Teq) for the tapered Ta2O5 layers and a severe dependence of RI sensitivity on Teq were obtained. Addition of 1 g of water in 100 g of a Chinese liquor (alcohol concentration = 46% (v/v)) was easily detected by the sensor. Monitoring of anti-human IgG adsorption with a waveguide of Teq = 31.99 nm indicates that the antibody coverage required for inducing a phase-different change of Δϕ = π is less than 0.012 monolayer. The same waveguide presents a quasi-linear dependence of Δϕ on water temperature with the slope of d(Δϕ)/dT = −28.50°/°C to which the contribution by the thermo-optical effect of the waveguide is 4.24°/°C, equivalent to a liquid RI change of Δnc = 1.41 × 10−5. The interferometer exhibits the promising potential for chemical and biological analyses because of its outstanding characteristics.