Highly sensitive and selective detection of mercury ions based on up-conversion FRET from NaYF4:Yb3+/Er3+ nanophosphors to CdTe quantum dots

The detection of Hg2+ has attracted considerable attention because of the serious health and environmental problems caused by it. There has been progress in the development of fluorescence biosensors based on quantum dots (QDs) for the detection of Hg2+. However, most of them are valid only in aqueous solution rather than in human serum due to the influence of protein autofluorescence in serum excited by ultraviolet or visible light. Herein, we designed and synthesized a novel NaYF4:Yb3+, Er3+ upconversion nanoparticle (UCNP)/CdTe QD composite probe for Hg2+ detection. The NaYF4:Yb3+, Er3+ UCNPs were synthesized via a solvothermal method. By grafting the CdTe QD probe onto the surface of the NaYF4:Yb3+, Er3+ UCNP, a fluorescence resonance energy transfer (FRET) biosensor for determination of Hg2+ ions was obtained under the pumping of 980 nm infrared light, which was capable of overcoming autoluminescence from serum. The spectral response towards Hg2+ suggested that the fluorescence intensity of the QDs reduced linearly with increasing Hg2+ concentration. The sensor showed high selectivity, a low detection limit of 15 nM and good linear Stern-Volmer characteristics, both in the buffer and serum. This biosensor has great potential for real applications of Hg2+ detection in biological and analytical fields.