A universal colorimetric PCR biosensor based upon triplex formation with the aid of Ru(phen)2dppx2+

AuNPs-DNA probes remain a challenge to recognize the double-stranded DNA (dsDNA) from routine PCR product despite its success in the recognition of the single-stranded (ssDNA) DNA of asymmetry-PCR product. Here, a universal colorimetric PCR biosensor is established with oligonucleotide modified AuNPs by recognizing the dsDNA of PCR product based on triplex DNA formation with the assistance of a triplex DNA intercalator Ru(phen)2dppx2+. The strategy was applied to detect different length dsDNA, including short dsDNA 1 (49 bp) and long dsDNA 2 (321 bp), both of which had the good linear relationship between the absorbance and the logarithm of the concentration of the targets. Moreover, the limit of detection (LOD) for short and long length dsDNA was 0.5 pM and 0.05 fg, lower than those of the previously reported methods, respectively. This strategy also displayed high selectivity against dsDNA 1 and dsDNA 2. These results demonstrate a potential strategy to detect all length of dsDNA, providing new opportunities in the life science, diagnosis, and medicine.