Differential Interference Contrast-Based Interrogation of Plasmonic Gold Nanohole Arrays for Label-Free Imaging Sensing

Plasmonic nanostructures provide a robust platform for label-free, refractive-index-based optical sensing. Most readout strategies for plasmonic sensing rely on the measurement of angle, wavelength, or intensity changes. The phase response, though it changes much more abruptly at plasmonic resonances, has been rarely investigated because of the requirement of a more sophisticated optical arrangement. Here, we present a phase-based imaging approach using differential interference contrast (DIC) as means of label-free optical sensing with plasmonic nanohole arrays. We develop a colorimetric-based imaging readout and evaluate the refractive-index sensing capability using a layer-by-layer polyelectrolyte deposition model. We cross-validate the DIC imaging approach using the corresponding DIC intensity and reflectance spectrum as well as numerical simulation and show good agreement among different measurements. Our platform opens an avenue for exploiting the phase response of nanoplasmonic structures for rapid and multiplexed sensing application.