Anisotropic Fluorescence Emission and Photobleaching at the Surface of One-Dimensional Photonic Crystals Sustaining Bloch Surface Waves. II. Experiments

Photonic crystal (PC)-enhanced fluorescence has been proposed as a novel tool for early disease detection in liquid biopsy. Photobleaching of the emitters has never been deeply investigated, although its cross section is expected to increase because of the large field intensity enhancement in PC. Herein, we report on the experimental investigation of the anisotropic effects arising when fluorescence excitation and emission are coupled to differently polarized modes of the same PC structure. In particular, we experimentally characterized the anisotropic photobleaching taking place during the operation of one-dimensional PC (1DPC) biosensors sustaining Bloch surface waves (BSW) at their truncation edge. The experimental results are compared to the description provided by our theoretical model reported in a twin article. We demonstrate experimentally that photobleaching affects the response of a cancer biomarkers' detection assay and propose a procedure to compensate for it. Moreover, we describe the experimental use of BSW-coupled fluorescence and of the strong localization of the BSW at the 1DPC surface to selectively probe the rotational diffusion kinetics of proteins bound at the 1DPC surface with high spatial resolution and for different binding strengths.