A method for an ultrasensitive silver-based color staining of proteins described by Sammons et al. was applied to the detection of oligonucleotides on polyacrylamide gels with slight modifications in the method of fixation. With these modifications, we can stain even tetranucleotide bands such as dA
4. Furthermore, the sensitivity of staining of
Hae III fragments of φX 174 RF DNA is several times higher than with ethydium bromide staining. The sensitivity of this silver-staining differs markedly among various homo-oligonucleotides. The limit of detection of rA
10 or dA
10 is approximately 40pg per mm
2 of cross-sectional area. Homo-oligonucleotides, dG
10 and dC
10, are also detectable. However, the dT
10 band concentrated more than 1, 000-fold could not be detected on the polyacrylamide gel by silver staining. Thus, the silver staining method is very useful for the sensitive detection of oligonucleotides as short as tetranucleotides that are not stained by ethidium bromide.
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