Gel electrophoresis of micron-sized particles: a problem and a solution.

The gel electrophoresis of spherical particles with a radius above 0.2 micron has not been reported yet. In the present study, video phase-contrast light microscopy is used to observe the motion of individual latex spheres, 0.52 micron in radius, during electrophoresis in 0.1% agarose gels. At 2 V/cm, the spheres initially migrate in the direction of the electrical field. However, each sphere eventually undergoes a cessation of all motion. Brownian motion is restored when the electrical potential gradient is reduced to zero. Arrest can be prevented by periodically inverting the direction of the electrical field. These observations are explained by electrical field-induced steric trapping of the spheres by gel fibers. Inversion of the electrical field should assist the application of agarose gel electrophoresis to micron-sized cellular organelles and cells.