A device for performing gel electrophoresis, the device comprising: (i) a gel cassette comprising a front plate and a back plate, the front plate and the back plate each having an inner surface, a top edge, a bottom edge and two side edges, the front and back plates (12, 14) being fastened together along at least the two side edges, such that the inner surfaces are face-to-face with a spacing there between forming a gel chamber, wherein the inner surface of at least one of the front and back plates (12, 14) has a stepped configuration such that the at least one plate has a top portion and a bottom portion, wherein the top portion has a thickness at least 0.05 mm thinner than the bottom portion, such that the spacing forming part of the gel chamber between the plates (12, 14) is greater at the top portion than the spacing forming part of the gel chamber between the plates at the bottom portion; (ii) a gel matrix held within the gel chamber; and (iii) a comb inserted in the spacing at the top portion of the plates (12, 14), the comb having a spine and a plurality of teeth extending from the spine downwardly into the gel matrix to form a plurality of wells in the gel matrix upon removal of the comb for performing the gel electrophoresis, characterized in that - the plate-to-plate distance at the top portion is constant throughout the top portion; - the plurality of teeth extend downwardly into the gel matrix such that gaps between adjacent teeth of the plurality of teeth are filled with the gel matrix, the plurality of teeth having a thickness (t s) that is constant and substantially equal to the spacing (d 1) between the top portions of the plates (12, 14), such that the plurality of wells are bounded on opposite sides by the top portions of the plates and the gel matrix extending into the spacing at the top portion of the plates (12, 14). (i) a gel cassette comprising a front plate and a back plate, the front plate and the back plate each having an inner surface, a top edge, a bottom edge and two side edges, the front and back plates (12, 14) being fastened together along at least the two side edges, such that the inner surfaces are face-to-face with a spacing there between forming a gel chamber, wherein the inner surface of at least one of the front and back plates (12, 14) has a stepped configuration such that the at least one plate has a top portion and a bottom portion, wherein the top portion has a thickness at least 0.05 mm thinner than the bottom portion, such that the spacing forming part of the gel chamber between the plates (12, 14) is greater at the top portion than the spacing forming part of the gel chamber between the plates at the bottom portion; (ii) a gel matrix held within the gel chamber; and (iii) a comb inserted in the spacing at the top portion of the plates (12, 14), the comb having a spine and a plurality of teeth extending from the spine downwardly into the gel matrix to form a plurality of wells in the gel matrix upon removal of the comb for performing the gel electrophoresis, - the plate-to-plate distance at the top portion is constant throughout the top portion; - the plurality of teeth extend downwardly into the gel matrix such that gaps between adjacent teeth of the plurality of teeth are filled with the gel matrix, the plurality of teeth having a thickness (t s) that is constant and substantially equal to the spacing (d 1) between the top portions of the plates (12, 14), such that the plurality of wells are bounded on opposite sides by the top portions of the plates and the gel matrix extending into the spacing at the top portion of the plates (12, 14).