  In recent years, fluorescence correlation spectroscopy has been increasingly
applied for the study of polymer dynamics on the nanometer scale. The core idea
is to extract, from a measured autocorrelation curve, an effective mean-square
displacement function that contains information about the underlying
conformational dynamics. The paper presents a fundamental study of the
applicability of fluorescence correlation spectroscopy for the investigation of
nanoscale conformational and diffusional dynamics. We find that fluorescence
correlation spectroscopy cannot reliably elucidate processes on length scales
much smaller than the resolution limit of the optics used and that its improper
use can yield spurious results for the observed dynamics.
