Investigating Anomalous Diffusion Using Fluorescence Correlation Spectroscopy

POSTER

Abstract

Models used in fluorescence correlation spectroscopy (FCS) generally assume diffusion of a standard Fickian nature such that the mean square displacement (MSD,$\left\langle {\Delta r^2} \right\rangle )$ of the molecular diffusion is linearly proportional to time, i.e. $\left\langle {\Delta r^2} \right\rangle \propto t$. In complex systems the diffusion can be anomalous, which is commonly described \textit{via} a power law dependence of the MSD, i.e. $\left\langle {\Delta r^2} \right\rangle \propto t^\alpha $. When measuring anomalous dynamics using FCS, the correlation functions are typically measured over a single lengthscale and the anomalous exponent, $\alpha $, is recovered through curve fitting. The anomalous exponent accurately describes the time dependence of the diffusion over the measurement lengthscale, yet for the majority of experimental systems it has not yet been tested whether the dynamics predicted by the fit are actually observed over different lengthscales -- i.e. whether or not the assumed power law dynamics truly describe the system dynamics. We investigate using scanning FCS methods that simultaneously measure correlation functions over a range of lengthscales in order to determine how accurately the physical models describe the dynamics. We use simulations to test these methods and discuss their application for measuring drug delivery rates in biomedical hydrogels.

Authors

  • Neil Anthony

  • Milind Purohit

    Univ of South Carolina, Benedict College, Sc 29204, Univ. South Carolina, Benedict College, Univ South Carolina, GA Tech, Central Microscopy Research Facility, University of Iowa, Iowa City, Iowa 52242, USA, Department of Chemistry, University of Sri Jayewardenepura, Nugegoda, Sri Lanka, Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA, Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294, Department of Physics, University of Alabama at Birmingham, Birmingham, AL 35294, College of William \& Mary, Harvard University, Benedict College, SC 29204, Massachusetts Institute of Technology, University of Applied Science, Bielefeld, Germany, Francis Marion University, Physics Dept., Emory University, Emory University, Formerly Emory University, currently UCLA, Physics Department, Georgia State University, Univ. of Georgia, Dept. of Chemistry, Universidad Nacional de Quilmes, Argentina, Pr, Dr, Derpartment of Physics, Florida A\&M University, Tallahassee, FL-32307, Department of Physics, Emory University, Georgia Institute of Technology, Naval Research Laboratory, University of Alabama, Tsinghua University, Lawrence Berkeley National Laboratory, Vanderbilt University, Jagellonian Univ., Univ. of Bonn, North Carolina A\&T State Univ., North Carolina Central Univ., Duke Univ. and TUNL, Georgia State University, Dept of Physics, Emory University, Cell Biology Department, Emory University, Physics Department, Emory University, University of South Carolina