High-Resolution Prism/(TiO₂/SiO₂)³/MoSe₂ Bloch Surface Wave Biosensor Based on Bragg Structure

A dielectric Bragg structure is utilized based on a one-dimensional photonic crystal of alternating TiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/SiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers as a sensor. MoSe<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> termination layer is exploited to excite a Bloch surface wave (BSW) at its interface with the analyte. The light source excites the biosensor through a MgF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> prism at a wavelength of 1100 nm. The proposed biosensor operates based on the variation of the resonance angle due to changes in the refractive index of the biological material, i.e. from 1.33 to 1.34. For ten MoSe<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> monolayers, the detection sensitivity is obtained as 287 (°/RIU) with a linear regression coefficient of 0.9953. Correspondingly, the maximum and average values of the figure of merit (FoM) amount to 7316 and 6913 (1/RIU), respectively. By decreasing the number of monolayers, the linearity improves and the FoM increases remarkably at the cost of a reduction in the average sensitivity. Such large FoMs provide ultra-high resolutions to distinguish between analytes with very close refractive indices. This is useful in detecting slight changes in the cell concentrations within a host medium. No grating is used in the proposed sensor, which simplifies the fabrication process.