Ultrasensitive mercury(II) ion detection by europium(III)-doped cadmium sulfide composite nanoparticles.

With the biomolecule glutathione (GSH) as a capping ligand, Eu(3+)-doped cadmium sulfide composite nanoparticles were successfully synthesized through a straightforward one-pot process. An efficient fluorescence energy transfer system with CdS nanoparticles as energy donor and Eu(3+) ions as energy accepter was developed. As a result of specific interaction, the fluorescence intensity of Eu(3+)-doped CdS nanoparticles is obviously reduced in the presence of Hg(2+). Moreover, the long fluorescent lifetime and large Stoke's shift of europium complex permit sensitive fluorescence detection. Under the optimal conditions, the fluorescence intensity of Eu(3+) at 614 nm decreased linearly with the concentration of Hg(2+) ranging from 10 nmol L(-1) to 1500 nmol L(-1), the limit of detection for Hg(2+) was 0.25 nmol L(-1). In addition to high stability and reproducibility, the composite nanoparticles show a unique selectivity towards Hg(2+) ion with respect to common coexisting cations. Moreover, the developed method was applied to the detection of trace Hg(2+) in aqueous solutions. The probable mechanism of reaction between Eu(3+)-doped CdS composite nanoparticles and Hg(2+) was also discussed.