Nicking enzyme-assisted signal-amplifiable Hg 2+ detection using upconversion nanoparticles

A highly specific and sensitive isothermal method for mercury detection using DNA-conjugated upconversion nanoparticles is reported. A single-stranded DNA containing thymine bases, used as the Hg -capturing element through the formation of thymine-Hg -thymine complex, is covalently attached to the NaYF : Yb Tm nanoparticles. Luminescence resonance energy transfer takes place between the NaYF : Yb Tm nanoparticles as donor and DNA-intercalating SYBR Green I as the acceptor upon excitation of 980 nm. The sensitivity and selectivity toward Hg are enhanced using the nicking enzyme, Nt. Alwl, which leads to signal amplification. By monitoring the ratio of acceptor emission to a reference peak, the presence of Hg ions are quantitatively determined with a lower detection limit of 0.14 nM, which is much lower than the US Environmental Protection Agency (EPA) limit of Hg in drinking water.