Sensitive detection of miRNA by using hybridization chain reaction coupled with positively charged gold nanoparticles

Positively charged gold nanoparticles (+) AuNPs can adsorb onto the negatively charged surface of single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA). Herein, long-range dsDNA polymers could form based on the hybridization chain reaction (HCR) of two hairpin probes (H-1 and H-2) by using miRNA-21 as an initiator. (+) AuNPs could adsorb onto the negatively charged surface of such long-range dsDNA polymers based on the electrostatic adsorption, which directly resulted in the precipitation of (+) AuNPs and the decrease of (+) AuNPs absorption spectra. Under optimal conditions, miRNA-21 detection could be realized in the range of 20 pM-10 nM with a detection limit of 6.8 pM. In addition, (+) AuNPs used here are much more stable than commonly used negatively charged gold nanoparticles ((-) AuNPs) in mixed solution that contained salt, protein or other metal ions. Importantly, the assay could realize the detection of miRNA in human serum samples.