High performance liquid analyte sensing based on Bloch surface wave resonances in the spectral domain

Abstract

In this paper, we report a design of a truncated one-dimensional photonic crystal (1DPhC) comprising six bi-layers of TiO2/SiO2 with a termination layer of TiO2 to realize a highly sensitive liquid analyte sensor utilizing Bloch surface wave (BSW) resonances in the spectral domain. We demonstrate that the BSW excitation shows up as a dip for both p- and s-polarized waves. Reflectance response for a p-polarized BSW is due to the spectral interference with maximum depth, and resonance thus obtained is comparable in magnitude with surface plasmon resonance (SPR). In the theoretical analysis, the spectral reflectance, phase difference and its derivative are determined for aqueous solutions of NaCl when the refractive index (RI) is changed in a range of 1.3330–1.3482. We revealed that the BSW resonances for the p-polarized wave give a sensitivity of 1602 nm per RI unit (RIU) and figure of merit (FOM) of 106 RIU−1, respectively. For an s-polarized BSW, they are increased to 1933 nm/RIU and 434 RIU−1, respectively. Moreover, the theoretical results are experimentally verified, and very good agreement is confirmed. The spectral responses for aqueous solutions of NaCl with the RI up to 1.3547 give for the p-polarized BSW a sensitivity of 2022 nm/RIU and FOM of 109 RIU−1, respectively, and using the spectral derivative of the BSW phase difference, the FOM is increased to 301 RIU−1. BSW based sensors with responses in both polarizations thus represent an effective alternative to SPR sensors with advantages including a higher FOM and mechanical robustness.