In electrophoresis, proteins are separated in an electric field by virtue of their charge and size. Electrophoresis of macromolecules is normally carried out by applying a thin layer of a sample to a solution stabilized by a porous matrix. The matrix can be composed of a number of different materials including paper, cellulose, acetate, or gels made of starch, agarose, or polyacrylamide. Agarose and polyacrylamide can act as a size-selective sieve in the separation. However, polyacrylamide is the most common matrix for separating proteins, probably due to its versatile applications.