An improved staining method is described for staining a biopolymer such as a peptide, a protein, an RNA, a DNA, an oligosaccharide or a complex containing a peptide, a protein, an RNA, a DNA, or an oligosaccharide in a matrix. The method includes the step of moving a staining reagent into the matrix using an electric force. The staining time can be dramatically reduced relative to conventional technologies. The improved staining method can particularly be used, for example, to stain proteins after gel separation. Other related methods and related kits are also described.