Introduction

Abstract

Fluorescence correlation spectroscopy (FCS) is one of a family of fluctuation correlation methods that can measure the dynamics of molecular processes from observations of spontaneous microscopic fluctuations in molecular position or number density. Principally, these measurements are carried out on systems in thermodynamic equilibrium; but are also applicable to non-equilibrium steady states, an area that could merit future study. The driving forces for spontaneous fluctuations arise from thermal energy and the fluctuations have a stochastic variation of amplitude and time course. Therefore, to derive the macroscopic phenomenological parameters by which we conventionally measure transport and chemical reaction rates, e.g. diffusion coefficients and chemical rate constants, it is necessary to perform a statistical analysis on a large number of measurements of individual fluctuations. Typically, this statistical analysis takes the form of a correlation function, which yields information about both the time courses and amplitudes of the molecular processes taking place in the system.