Shukun Xu

A novel approach for the rapid determination of ascorbic acid was developed based on the direct luminescence quenching of LaF₃:Ce,Tb nanoparticles. The LaF₃:Ce,Tb nanoparticles were synthesized via a microwave-assisted method with ionic liquids (BmimBF₄) as the fluorine source. The as-prepared nanoparticles were uniformly ellipsoidal with an average size of about 12 nm. They are water soluble and highly fluorescent under 249 nm excitation. A new method for the rapid determination of ascorbic acid was established based on the large degree of overlap between the excitation spectrum of LaF₃:Ce,Tb nanoparticles and the absorption spectrum of ascorbic acid. Ascorbic acid exhibits a broad band from 200 to 300 nm with the maximum absorption at 260 nm, which can absorb the excitation light of LaF₃:Ce,Tb nanoparticles, consequently resulting in the luminescence quenching. The results showed a good inverse linear relationship between the luminescent intensity of LaF₃:Ce,Tb nanoparticles and the concentration of ascorbic acid in the range 8.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ (R = 0.9995), with the detection limit of 2.4 × 10⁻⁶ mol L⁻¹ and a RSD of 0.5% (5.33 × 10⁻⁵ mol L⁻¹, n = 11). Compared with the standard redox titration method, our new method is effective for the determination of ascorbic acid.

Fe-doped TiO₂nanotubes (Fe-TNTs) have been prepared by ultrasonic-assisted hydrothermal method. The structure and composition of the as-prepared TiO₂nanotubes were characterized by transmission electron microscopy, X-ray diffraction, and UV-Visible absorption spectroscopy. Their photocatalytic activities were evaluated by the degradation of MO under visible light. The UV-visible absorption spectra of the Fe-TNT showed a red shift and an enhancement of the absorption in the visible region compared to the pure TNT. The Fe-TNTs were provided with good photocatalytic activities and photostability and under visible light irradiation, and the optimum molar ratio of Ti : Fe was found to be 100 : 1 in our experiments.

In the present work, CdS quantum dots (QDs) were successfully biosynthesized at room temperature by using saccharomyces cerevisiae yeast as a carrier. Fluorescence emission spectra, ultraviolet-visible (UV/Vis) absorption spectra, and inverted fluorescence microscope images confirmed that saccharomyces cerevisiae can be used to biosynthesize CdS QDs. The as-prepared CdS QDs show the fluorescence emission peak at 443 nm and emit blue-green fluorescence under UV light (with excitation at 365 nm). Transmission electron microscopy (TEM) was applied to characterize the as-prepared CdS QDs and the TEM results showed that the as-prepared CdS QDs had the structure of hexagonal wurtzite. Fluorescence emission spectrum and UV/Vis absorption spectrum were used as the performance indicatiors to study the effects of saccharomyces cerevisiae yeast incubation times, reactant Cd2+ concentrations and reaction times on CdS QDs synthesis. Saccharomyces cerevisiae yeast grown in early stable phase can get the highest fluorescence intensity of CdS QDs when they were co-cultured with 0.5 mmol x L(-1) of Cd2+ with 24 h incubation time. Furthermore, much more CdS QDs can be obtained by changing the culture medium during the synthesis process.

This work reports the novel microwave-assisted solvothermal synthesis and structural, topographic, spectroscopic characterization of NaYF₄:Yb,Er upconversion nanoparticles (UCNPs) as well as their application in the labeling of HeLa cells. The nanoparticles were prepared in ethylene glycol, with rare earth acetates as precursor and NH₄F and NaCl as the fluorine and sodium sources. X-ray diffraction, transmission electron microscopy, and luminescence spectroscopy were applied to characterize the nanoparticles. Experimental results showed that the microwave-assisted solvothermal method is an effective approach to create highly crystalline, strongly luminescent UCNPs at a lower temperature (160 °C) and within a significantly shortened reaction time (only 1 h) compared to the traditional methods. The effect of fluorine source on the optical properties of UCNPs was investigated by using NH₄F, NH₄HF₂, NaF, and 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF₄) as different fluorine sources; NH₄F proved to be the best one, making the luminescent intensity increase at least 2 orders of magnitude. The UCNPs with four different colors (green, yellow, orange, and cyan) were successfully obtained. After being modified with amino groups and coupled with CEA-8 antibody, the obtained nanoparticles were successfully applied in the specific fluorescent immunolabeling and imaging of HeLa cells to further verify their function as a marker in immunolabeling.