Journal Article

Scattering fingerprints of two-state dynamics

Krapf, Diego, Godec, Aljaž, Dieball, Cai, Weiss, Matthias

2022

Overview

Particle transport in complex environments such as the interior of living cells is often (transiently) non-Fickian or anomalous, that is, it deviates from the laws of Brownian motion. Such anomalies may be the result of small-scale spatio-temporal heterogeneities in, or viscoelastic properties of, the medium, molecular crowding, etc. Often the observed dynamics displays multi-state characteristics, i.e. distinct modes of transport dynamically interconverting between each other in a stochastic manner. Reliably distinguishing between single- and multi-state dynamics is challenging and requires a combination of distinct approaches. To complement the existing methods relying on the analysis of the particle’s mean squared displacement, position- or displacement-autocorrelation function, and propagators, we here focus on ‘scattering fingerprints’ of multi-state dynamics. We develop a theoretical framework for two-state scattering signatures—the intermediate scattering function and dynamic structure factor—and apply it to the analysis of simple model systems as well as particle-tracking experiments in living cells. We consider inert tracer-particle motion as well as systems with an internal structure and dynamics. Our results may generally be relevant for the interpretation of state-of-the-art differential dynamic microscopy experiments on complex particulate systems, as well as inelastic or quasielastic neutron (incl. spin-echo) and x-ray scattering probing structural and dynamical properties of macromolecules, when the underlying dynamics displays two-state transport.

• Publisher: IOP Publishing
• Subject: Anomalies / Autocorrelation functions / Brownian motion / Cells (biology) / diffusion / Displays / dynamic structure factor / Dynamics / Experiments / Fingerprints / Fourier transforms / fractional Brownian motion / Gaussian network model / Indoor environments / Inelastic scattering / intermediate scattering function / Laplace transforms / Macromolecules / Microscopy / Particle motion / Physics / Scattering functions / segmentation / Structure factor / Tracer particles / two-channel processes / Viscoelasticity / X-ray scattering