Analyte-triggered cyclic autocatalytic oxidation amplification combined with anupconversion nanoparticle probe for fluorometricdetection of copper(II).

Abstract

The authors describe an upconversion nanoparticle-based (UCNP-based) fluorometric method for ultrasensitive and selective detection of Cu2+. The UCNPs show a strong emission band at 550nm under near-infrared excitation at 980nm. The principle of the strategy is that gold nanoparticles (AuNP) can quench the fluorescence of UCNP. In contrast, the addition of L-cysteine (Cys) can induce the aggregation of AuNP, resulting in a fluorescence recovery of theUCNPs. On addition of Cu2+, it oxidizes Cys to cystine and is reduced to Cu+. The Cu+ thusformedcan be oxidized cyclically to Cu2+ by dissolved O2, which catalyzes and recycles the whole reaction. Thus, the aggregation of AuNP is inhibited and the fluorescence recovered by Cys is quenched. Under the optimal condition, the quenching efficiency shows a good linear response to theconcentrations of Cu2+ in the 0.4-40nM range. The limit of detection is 0.16nM, which is 5 orders of magnitude lower than the U.S. Environmental Protection Agency limit for Cu2+ in drinking water (20μM). The method has been further applied to monitor Cu2+ levels in real samples. The results of detection are wellconsistent with those obtained by atomic absorption spectroscopy. Graphical abstract Gold nanoparticles (AuNP) as a high efficient fluorescence quenching reagent of upconversion nanoparticles (UCNP) were used in a fluorometric method for detection of Cu2+ based on acyclic catalytic oxidation amplification strategy.