A novel DNA detection using spherical identification probe and strand displacement reaction-initiated silver nanocluster switch.

Herein, we developed a novel fluorescent assay using spherical identification probes and toehold-mediated strand displacement reaction-initiated silver nanoclusters (AgNCs) "on-off" signal switch. In this strategy, the target was captured by the spherical probes to induce the activity of exonuclease III (Exo III), catalyzing the cyclic cleavage of substrates to produce a mass of trigger strands. After magnetic bead separation, the intermediates in the supernatant activated downstream toehold-mediated strand displacement reaction to change the structure of silver nanocluster templates, leading to fluorescence intensity reduction. Furthermore, it is demonstrated that the application of spherical identification probes could reduce the signal leakage and the limit of detection. In addition, AgNCs with perfect optical property were ingeniously combined to realize signal output, which reduced the cost and time of synthesis. Under the optimal conditions, the sensing method displayed a good linear range from 250 pM to 25 nM with a detectable minimum concentration of 250 pM. And the practical application potential in complex biological matrices was also evaluated. Considering these advantages, this constructed strategy opens a new path for nucleic acid detection with better performance. A simple, label- and hairpin-free fluorescent system based on spherical identification probe and toehold-mediated strand displacement reaction-initiated silver nanoclusters (AgNCs) "on-off" signal switch was successfully constructed to detect target DNA.