Translational dynamics of fluorescently labeled species by Fourier imaging correlation spectroscopy

Time-dependent spatial distributions of density fluctuations in synthetic and biological systems are determined from purely incoherent fluorescence signals. This is accomplished using a new method, Fourier imaging correlation spectroscopy (FICS), that is based on the detection of modulated fluorescence signals and measures temporal fluctuations of a spatial Fourier component of the sample particle number density. The information contained by FICS measurements provides details about the spatial relationship between fluorescent species, usually only obtained by direct imaging single-particle experiments. The FICS approach offers significant advantages in signal-to-noise detection efficiency, allowing a broader dynamic range to be accessed experimentally.