In this study, we describe a sensitive staining method for DNA in agarose and polyacrylamide gels using organic visible dyes, indoine blue (IB) and methyl orange (MO). The counterion-dye staining method uses two oppositely charged dyes to form a hydrophobic ion pair complex in the staining solution. A decrease in the number of free forms of dyes in staining solution can enhance the selectivity of binding between the dye and DNA, and can reduce nonspecific background staining. As a result, the sensitivity of counterion-dye staining was significantly improved compared with other dye-based staining. This method uses a staining solution consisting of 0.008% IB, 0.002% MO, 10% ethanol and 0.2 M sodium acetate at pH 4.7, and can detect 5 ng of lambda DNA/HindIII within 60 min in agarose gels and 10 ng of PhiX174 DNA/HaeIII within 20 min in polyacrylamide gels.
