A DNA-stabilized silver nanoclusters/graphene oxide-based platform for the sensitive detection of DNA through hybridization chain reaction

A silver nanoclusters (AgNCs)/graphene oxide (GO)-based fluorescence sensor was developed for label-free DNA detection through hybridization chain reaction (HCR). A DNA sequence associated with the human immunodeficiency virus (HIV) was selected as a model target. Two DNA probes , hairpin probe 1 (H 1 ) and hairpin probe 2 (H 2 ), were partially complementary. GO was used as an adsorption material to capture the hairpin probes and a selective fluorescence quencher was used to reduce the background signal. Upon addition of AgNO 3 and NaBH 4 , the AgNCs were synthesized at the terminals of the H 1 and H 2 probes. In the absence of target DNA (T HIV ), hybridization chain reaction (HCR) could not be triggered due to the stability of H 1 and H 2 probes. The hairpin probe-protected AgNCs attached to the GO surface, efficiently quenching fluorescence of the AgNCs. Therefore, the system showed very low background. In presence of T HIV , the target triggered the chain-like assembly of H 1 and H 2 through HCR, generating a long chain of H 1 and H 2 complexes. The HCR product (AgNCs nanowires) could not be adsorbed on the surface of GO; hence, it generated a strong fluorescent signal based on the concentration of the target. Under the optimized conditions, the detection limit of the fluorescence sensor was 1.18   nM, and hence it can be applied to clinical samples.