Methods for deriving a diffusion coefficient and a drift velocity characterizing an ensemble of particles. A time series of images is acquired, and each image is Fourier transformed. An autocorrelation function is computed and fit to an exponential decay for each wave vector on a grid. A model of the diffusion-advection equation allows the decay rate Γ, expressed as a dispersion map over the wave vector plane, to yield both a diffusion coefficient and a mean drift velocity. As an example, the particles may be fluorescently excited probes where the probes label intracellular elements.
Dispersion-Relation Fluorescence Spectroscopy