First-passage statistics of confined colloids

TL;DR

This study explores how confinement geometries influence the first-passage times of diffusing particles, revealing that confinement can either accelerate or hinder target finding depending on direction, with implications for chemical and biological processes.

Contribution

It combines advanced holographic microscopy and statistical inference to experimentally and numerically analyze confinement effects on first-passage statistics with nanometric precision.

Findings

Wall-normal target finding is accelerated by confinement.

Confinement induces non-Gaussian displacement statistics.

Rare large displacements increase first-passage probability.

Abstract

The encounter of diffusing entities underlies a wide range of natural phenomena. The dynamics of these first-passage dynamics are strongly influenced by confining geometries. Confinement modifies microscopic diffusion through conservative and hydrodynamic interactions, making it essential for realistic modeling. In this Letter, we investigate how confinement affects the first-passage statistics of a diffusing particle. Using \textit{state-of-the-art} holographic microscopy combined with advanced statistical inference, we probe this motion with nanometric precision. Our experimental and numerical results show that confinement can either hinder or enhance first-passage kinetics, depending on the spatial direction. In particular, wall-normal target finding is accelerated by confinement-induced non-Gaussian displacement statistics, which increases the probability of rare, large displacements, with implications for confined chemical reactions and biological \textit{winners-take-all} processes near boundaries.