A label-free colorimetric platform for DNA via target-catalyzed hairpin assembly and the peroxidase-like catalytic of graphene/Au-NPs hybrids.

A target-catalyzed hairpin assembly (CHA) and graphene/Au-NPs hybrids-based platform has been developed for the determination of DNA. This new sensor not only avoided any labeling but also reduced the background signal. In the absence of target, the assembly of H1 and H2 couldn't be triggered. The catalytic activity of graphene/Au-NPs hybrids was inhibited by adsorption of H1 and H2, leading to the "inactive" hybrids unable to catalyze the oxidation reaction of 3,3',5,5'-tetramethylbenzidine (TMB). However, with the addition of target DNA, the target-catalyzed hairpin assembly was initiated and produced plenty of H1-H2 duplex, which had a weak binding affinity with the graphene/Au-NPs. Thus, the protected interface of graphene/Au-NPs hybrids became active and catalyzed the oxidation reaction of TMB accompanied with a colorless to-blue color change. This approach exhibited good sensitivity and specificity for target DNA with a detection limit of 5.74 × 10(-11) M, and realized the assay of target DNA in human serum samples. Besides, this sensor could be further expanded to detect viruses or proteins by adapting the corresponding aptamers, showing great potential in biochemical detections.