Widefield phototransient imaging for visualizing 3D motion of resonant particles in scattering environments

TL;DR

This paper introduces a novel ultrafast holographic transient microscopy technique that enables 3D visualization and tracking of resonant nanoparticles in scattering environments, with potential applications in biological and material sciences.

Contribution

The work demonstrates the first combined use of ultrafast holographic transient microscopy for distinguishing, localizing, and tracking multiple nanoparticles in 3D within scattering media.

Findings

Successfully distinguished dielectric from metallic nanoparticles based on phototransient signals.

Achieved 3D localization of single particles over large volumes with high temporal resolution.

Tracked multiple gold nanoparticles simultaneously in scattering environments.

Abstract

Identifying, visualising and ultimately tracking dynamically moving non-fluorescent nanoparticles in the presence of non-specific scattering is a long-standing challenge across the nano- and life-sciences. In this work we demonstrate that our recently developed ultrafast holographic transient (UHT) microscope is ideally suited for meeting this challenge. We show that UHT microscopy allows reliably distinguishing off-resonant, dielectric, from resonant, metallic, nanoparticles, based on the phototransient signal: a pre-requisite for single-particle tracking in scattering environments. We then demonstrate the capability of UHT microscopy to holographically localize in 3D single particles over large volumes of view. Ultimately, we combine the two concepts to simultaneously track several tens of freely diffusing gold nanoparticles, within a 110x110x110 $\mu$m volume of view at an integration time of 10 ms per frame, while simultaneously recording their phototransient signals. The combined experimental concepts outlined and validated in this work lay the foundation for background-free 3D single-particle tracking applications or spectroscopy in scattering environments and are immediately applicable to systems as diverse as live cells and tissues or supported heterogeneous catalysts.