Particle image correlation spectroscopy (PICS) Retrieving nanometer-scale correlations from high-density single-molecule position data

¹ Leiden University
² University of Leiden

^* To whom correspondence should be addressed. E-mail: schmidt{at}physics.leidenuniv.nl.

Submitted on July 6, 2006
Revised on August 11, 2006
Accepted on 11 October 2006

	Abstract

A new data analysis tool that resolves correlations on the nanometer length and millisecond time scale is derived. This tool, adapted from methods of spatiotemporal image correlation spectroscopy, exploits the high positional accuracy of single-particle tracking. While conventional tracking methods break down if multiple particle trajectories intersect, our method works in principle for arbitrarily large molecule densities and diffusion coefficients as long as individual molecules can be identified. The method is computationally cheap and robust and requires no a priori knowledge about the dynamical coefficients, as opposed to other methods. We demonstrate the validity of the method by Monte Carlo simulations and by application to singlemolecule tracking data of membrane-anchored proteins in live cells. The results faithfully reproduce those obtained by conventional tracking. Upon activation, a fraction of the small GTP-ase H-Ras is confined to domains of < 200 nm diameter which further substantiates the prediction that membrane organization is a determinant in cellular signaling

Key Words: correlation spectroscopy, diffusion, membrane inhomogeneities, single-molecule