Primer dimers may be visible after gel electrophoresis of the PCR product. PDs in ethidium bromide-stained gels are typically seen as a 30-50 base-pair (bp) band or smear of moderate to high intensity and distinguishable from the band of the target sequence, which is typically longer than 50 bp.
In quantitative PCR, PDs may be detected by melting curve analysis with intercalating dyes, such as SYBR Green I, a nonspecific dye for detection of double-stranded DNA. Because they usually consist of short sequences, the PDs denature at lower temperature than the target sequence and hence can be distinguished by their melting-curve characteristics.