Brownian Motion and Electrophoretic Transport in Agarose Gels Studied by Epifluorescence Microscopy and Single Particle Tracking Analysis

The motion of fluorescent latex beads and circular DNA in agarose gels is investigated by epifluorescence computer-enhanced microscopy. The individual trajectories are obtained and the diffusion dynamics are determined by averaging over an ensemble of trajectories. It was found that the diffusion of latex beads in agarose gels is characterized by the scaling relation ( ) 2 ∼ t 2/ d W with d W = 3.1 ± 0.3, in the gel concentration range 0.6%−1.2%. This indicates that the structure of the holes in agarose gels is fractal on the scale from 0.2 to 15 μm that has been studied and different from those of percolating clusters. If an electric field is applied, d W measured in the direction of the field decreases and can even reach values lower than 2; this means that the diffusion increases at long time. The mobility vs gel concentration graph is found to be well fitted with a polynomial expression in agreement with recent computer calculations. Finally our preliminary results on DNA show that the motion of M13 circular DNA molecules is governed by the same dependencies as those of the latex particles.