Optical Route for Testosterone Hormone Sensing Exploiting BlochWaves in One Dimensional Photonic Crystal

Bloch surface waves (BSWs) in periodic multilayer photonic crystals (PCs) were excited using a 635-nm laser for testosterone hormone detection employing the Kretschmann-Raether configuration. A 24-layer ZrO2-SiO2 PC served as the key dielectric sensing medium for the evanescent field interaction with testosterone molecules in blood plasma. Although SiO2 does not bind strongly to testosterone, it provides the necessary low-index component to achieve high contrast with ZrO2. The layer combinations are ideal for low optical loss in biosensing. A 20-μL mixture of phosphate buffered saline, testosterone, and blood plasma with the testosterone concentrations of 0.5, 1, 10, 100, and 200 mM were poured over the PC surface. The acceptable viscosity of this mixture helps adhere the BSW-based sensor to the BK7 prism coupler surface used in the experiment. The results of polarized reflected transverse magnetic waves indicate strong dependence on the angular shift. The lowest concentration (of 0.5 mM) was detected at an angle of approximately 51.2°, while the highest concentration (of 200 mM) was spotted at 51.7°. For concentrations < 10 mM, the sensitivity of the studied BSW-based sensor was found to be nonlinear with the angular shift; higher concentrations, however, showed this feature to be linear.