Inclusion of the tunneling phase shift for interferometric particle imaging for bubble sizing

The interferometric particle imaging technique makes use of the angular oscillations of the scattered light in the forward direction for droplet or bubble sizing.The out-of-focus image consists of fringes,the spacing of which reflects the interference between the surface-reflected light and the twofold-refracted light.Total internal reflection occurs when the incident light hits the bubble at a large incident angle.The tunneling phase shift is not included in the geometric optics approximation,which leads to a deviation from Mie theory.In this work,we modified the formula for describing the fringe spacing by including the tunneling phase shift of total internal reflection.Numerical analysis and experiments showed that the modification is effective for the measurement of bubbles smaller than 60μm.

Phase-sensitive plasmonic biosensor using a portable and large field-of-view interferometric microarray imager

Nanophotonics,and more specifically plasmonics,provides a rich toolbox for biomolecular sensing,since the engineered metasurfaces can enhance light–matter interactions to unprecedented levels.So far,biosensing associated with high-quality factor plasmonic resonances has almost exclusively relied on detection of spectral shifts and their associated intensity changes.However,the phase response of the plasmonic resonances have rarely been exploited,mainly because this requires a more sophisticated optical arrangement.Here we present a new phase-sensitive platform for high-throughput and label-free biosensing enhanced by plasmonics.It employs specifically designed Au nanohole arrays and a large field-of-view interferometric lens-free imaging reader operating in a collinear optical path configuration.This unique combination allows the detection of atomically thin(angstrom-level)topographical features over large areas,enabling simultaneous reading of thousands of microarray elements.As the plasmonic chips are fabricated using scalable techniques and the imaging reader is built with low-cost off-the-shelf consumer electronic and optical components,the proposed platform is ideal for point-of-care ultrasensitive biomarker detection from small sample volumes.Our research opens new horizons for on-site disease diagnostics and remote health monitoring.

Prediction of photothermal phase signatures from arbitrary plasmonic nanoparticles and experimental verification

We present a new approach for predicting spatial phase signals originating from photothermally excited metallic nanoparticles of arbitrary shapes and sizes.The heat emitted from such a nanoparticle affects the measured optical phase signal via changes in both the refractive index and thickness of the nanoparticle surroundings.Because these particles can be bio-functionalized to bind certain biological cell components,they can be used for biomedical imaging with molecular specificity,as new nanoscopy labels,and for photothermal therapy.Predicting the ideal nanoparticle parameters requires a model that computes the thermal and phase distributions around the particle,thereby enabling more efficient phase imaging of plasmonic nanoparticles and avoiding trial-and-error experiments while using unsuitable nanoparticles.The proposed nonlinear model is the first to enable the prediction of phase signatures from nanoparticles with arbitrary parameters.The model is based on a finite-volume method for geometry discretization and an implicit backward Euler method for solving the transient inhomogeneous heat equation,followed by calculation of the accumulative phase signal.To validate the model,we compared its results with experimental results obtained for gold nanorods of various concentrations,which we acquired using a custom-built wide-field interferometric phase microscopy system.