Determination of a particle's radius by two-dimensional agarose gel electrophoresis

Electrophoresis in an agarose gel dilute enough to be almost nonretarding, followed by electrophoresis in an orthogonal direction into a more concentrated agarose gel, has been developed as a procedure to determine the radius of spherical particles. Unlike procedures of unidirectional electrophoresis in a single gel, the above procedure can be used to compare the radii of particles that differ in solid-support-free electrophoretic mobility. Accuracy of 0.3 nm has been achieved with particles 30 nm in radius. It was found that the apparent radius of the spherical capsid of bacteriophage P22 decreased by 3% during elevated temperature-induced ejection of DNA from the capsid. Though originally designed for use with multimolecular paricles, the procedure described here should also be useful with monomolecular particles.