Nicking enzyme-assisted signal-amplifiable Hg2+ detection using upconversion nanoparticles

Abstract

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 Hg²⁺-capturing element through the formation of thymine-Hg²⁺-thymine complex, is covalently attached to the NaYF₄: Yb^3+, Tm³⁺ nanoparticles. Luminescence resonance energy transfer takes place between the NaYF₄: Yb^3+, Tm³⁺ nanoparticles as donor and DNA-intercalating SYBR Green I as the acceptor upon excitation of 980 nm. The sensitivity and selectivity toward Hg²⁺ 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 Hg²⁺ 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 Hg²⁺ in drinking water.

Keywords: Luminescence resonance energy transfer (LRET); Mercuric ion; Nicking enzyme; Signal amplification; Upconversion nanoparticles (UCNPs).