Probing single DNA mobility with fluorescence correlation microscopy.

Fluorescence correlation spectroscopy combined with microscopy (FCSM) is used to study the mobility of DNA fragments in aqueous solution and tissue models on the single molecule level. The effective hydrodynamic radius was measured for various lengths of ds-DNA chains and obeyed the theoretically inveterate [DNA length](0.5) relationship. Hindered diffusion of ds-DNA through the gel matrix of various densities is thought of as an extension of Kramer's problem for a flexible polymer chain. With increasing DNA length the average barrier crossing time rises as [DNA length](2) and this agrees with theory predictions for polymer molecules surmounting an entropic barrier.