Enzyme-free and label-free miRNA detection based on target-triggered catalytic hairpin assembly and fluorescence enhancement of DNA-silver nanoclusters

We herein describe a simple, enzyme-free, and label-free strategy for the detection of miRNA based on target-triggered catalytic hairpin assembly (CHA) and fluorescence enhancement of DNA-silver nanoclusters (DNA-AgNCs). This strategy employs two hairpin probes that are rationally designed to contain AgNCs and guanine (G)-rich DNA sequence, respectively. In principle, the two hairpin probes, which exist independently, form a hybridized complex in the presence of target miRNA through CHA reaction, thereby inducing strong fluorescence signal of AgNCs by the presence of G-rich sequence placed in close proximity. Importantly, target miRNA is released after the first CHA reaction, which promotes another CHA reaction, consequently leading to the significantly enhanced fluorescence signal of AgNCs. Based on this one-step, homogeneous, and isothermal amplification method, we successfully detected the target miRNA with high selectivity and sensitivity. In addition, the practical applicability of this strategy was also demonstrated by analyzing the target miRNA in human serum.