Dual fluorescence resonance energy transfer assay between tunable upconversion nanoparticles and controlled gold nanoparticles for the simultaneous detection of Pb2+ and Hg2+

In this work, we presented a novel dual fluorescence resonance energy transfer (FRET) system for the simultaneous detection of Pb2+ and Hg2+. This system employed two color upconversion nanoparticles (UCNPs) as the donors, and controlled gold nanoparticles (AuNPs) as the acceptors. The two donor-acceptor pairs were fabricated by hybridizing the aptamers and their corresponding complementary DNA. Thus, the green and red upconversion fluorescence could be quenched because of a good overlap between the UCNPs fluorescence emission and the AuNPs absorption spectrum. In the presence of Pb2+ and Hg2+, the aptamers preferred to bind to their corresponding analytes and formed a G-quadruplexes structure for Pb2+ and the hairpin-like structure for Hg2+. As a result, the dual FRET was disrupted, and the green and red upconversion fluorescence was restored. Under optimized experimental conditions, the relative fluorescence intensity increased as the metal ion concentrations were increased, allowing for the quantification of Pb2+ and Hg2+. The relationships between the fluorescence intensity and plotting logarithms of ion concentrations were linear in the range from 0.1 to 100 nM for Pb2+ and 0.5 to 500 nM for Hg2+, and the detection limits of Pb2+ and Hg2+ were 50 pM and 150 pM, respectively. As a practical application, the aptasensor was used to monitor Pb2+ and Hg2+ levels in naturally contaminated samples and human serum samples. Ultimately, this type of dual FRET could be used to detect other metal ions or contaminants in food safety analysis and environment monitoring. (C) 2014 Elsevier B.V. All rights reserved.