According to embodiments of the present invention, a microfluidic device for gel electrophoresis is provided. The microfluidic device includes a sample channel configured to receive a sample; a stacking channel comprising a preloaded stacking reagent; and a separation channel comprising a preloaded separation reagent, wherein the preloaded stacking reagent has a physical characteristic different from that of the preloaded separation reagent; and wherein the sample channel, the stacking channel and the separation channel are in fluid communication with one another. According to further embodiments of the present invention, a method of manufacturing a microfluidic device for gel electrophoresis is also provided.