Ultrasensitive Label-Free Resonance Rayleigh Scattering Aptasensor for Hg2+ Using Hg2+-Triggered Exonuclease III-Assisted Target Recycling and Growth of G-Wires for Signal Amplification

A novel signal-on and label-free resonance Rayleigh scattering (RRS) aptasensor was constructed for detection of Hg2+ based on Hg2+-triggered Exonuclease III-assisted target recycling and growth of G-quadruplex nanowires (G-wires) for signal amplification. The hairpin DNA (H-DNA) was wisely designed with thymine-rich recognition termini and a G-quadruplex sequence in the loop and employed as a signal probe for specially recognizing trace Hg2+ by a stable T-Hg2+-T structure, which automatically triggered Exonuclease III (Exo-III) digestion to recycle Hg2+ and liberate the G-quadruplex sequence. The free G-quadruplex sequences were self-assembled into guanine nanowire (G-wire) superstructure in the presence of Mg2+ and demonstrated by gel electrophoresis. The RRS intensity was dramatically amplified by the resultant G-wires, and the maximum RRS signal at 370 nm was linear with the logarithm of Hg2+ concentration in the range of 50.0 pM to 500.0 nM (R = 0.9957). Selectivity experiments revealed that the as-prepared RRS sensor was specific for Hg2+, even coexisting with high concentrations of other metal ions. This optical aptasensor was successfully applied to identify Hg2+ in laboratory tap water and river water samples. With excellent sensitivity and selectivity, the proposed RRS aptasensor was potentially suitable for not only routine detection of Hg2+ in environmental monitoring but also various target detection just by changing the recognition sequence of the H-DNA probe.