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.

Determination of formaldehyde in aqueous solutions by a novel fluorescence energy transfer system.

An efficient fluorescence energy transfer (FET) system between CePO(4):Tb(3+) nanocrystals as donor and 6-mercapto-5-triazole[4,3-b]-S-tetrazine as acceptor was built. CePO(4):Tb(3+) nanocrystals were synthesized in aqueous solutions, and characterized by transmission electron microscopy, electron diffraction pattern spectroscopy and spectrofluorometry. Under alkaline conditions, 6-mercapto-5-triazole[4,3-b]-S-tetrazine was generated by redox reaction of formaldehyde (HCHO) with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT) at room temperature. The degree of the overlap was effective for FET between the emission spectrum of CePO(4):Tb(3+) and the absorption spectrum of 6-mercapto-5-triazole[4,3-b]-S-tetrazine. Based on this system, a simple and sensitive fluorescence method for the selective determination of formaldehyde in aqueous solutions was developed. Under optimal conditions, the quenched fluorescence intensity increased linearly with the concentration of HCHO ranging from 1.03 x 10(-9) to 1.03 x 10(-5) mg mL(-1) with a correlation coefficient of 0.9976. The limit of detection was 1.65 x 10(-10) mg mL(-1). Compared with several methods, the proposed method had a wider linear range, higher selectivity and sensitivity. Moreover, analytical application of the method was demonstrated by water samples.