A Competitive Strategy Coupled with Endonuclease‐Assisted Target Recycling for DNA Detection Using Silver‐Nanoparticle‐Tagged Carbon Nanospheres as Labels

A simple competitive strategy was designed for the sensitive detection of sequence-specific DNA by combining endonuclease-assisted target recycling and electrochemical stripping analysis of silver nanoparticles (AgNPs). The AgNP-tagged carbon nanospheres were synthesized by means of in situ reduction of Ag(+) adsorbed onto a negatively charged polyelectrolyte layer and functionalized with streptavidin for binding biotin-labeled DNA strands. The labeled strand was captured on the DNA sensor surface by competitive hybridization of biotinated primer 1 and its cleaved product. The cleaved product could be amplified in homogeneous solution by endonuclease-assisted target recycling with a Y-shaped junction DNA structure, thus leading to the correlation of the stripping signal to the target concentration. The functionalized nanosphere was characterized with X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The proposed method showed a linear range from 0.1 to 1000 fM with a limit of detection of 0.066 fM (3σ) and good selectivity for base discrimination. The designed strategy provided a sensitive tool for DNA analysis and could be widely applied in bioanalysis and biomedicine.