Synthesis Of NaGdF₄:Eu Rare Earth Fluorescent Nanoparticles And Its Application In Analysis

Rare earth fluorescent nanoparticles have the advantages of large Stokes shift, high fluorescence emission intensity, narrow half emission peaks and long fluorescence lifetime. Being used as probes of biological molecules, they have greater sensitivity and selectivity. In this paper, we attempt to synthesize rare-earth inorganic fluorescent nanoparticles with high fluorescence intensity, good dispersion, no reunion and long-time stability, and study their exploratory application in analysis.In this paper, the NaGdF4:Eu fluorescent nanoparticles were synthesized by hydrothermal method. The effects of experimental conditions, such as the reaction temperature and time, the pH values and mole ratio of the reactants and the percentage of europium ion doping concentrations on fluorescent characters of NaGdF4:Eu nanoparticles were studied. The results showed that the best conditions to synthesize NaGdF4:Eu nanoparticles were as follows:the reactants reacted at 140℃for 4h; the pH values of rare earth ions, sodium citrate and sodium fluoride solution were 2.0,6.5 and 10.0 respectively; the mole ratio of rare earth ions, sodium citrate and sodium fluoride was 4:6:10; the Eu3+ doped content (the doped content is the rate of Eu3+ mol in the total mol of rare earth ions) was 30%.The prepared NaGdF4:Eu particles were charactered by IR, XRD, TEM and particle size distribution. The results of IR showed that the surface of the NaGdF4:Eu nanoparticles were covered with sodium citrate; the results of XRD showed that the prepared NaGdF4:Eu particles were hexagon and the average diameter of NaGdF4:Eu nanoparticles was 11 nm with good crystallization. TEM indicated that the decentralization of the prepared NaGdF4:Eu nanoparticles was good and the image of the electron diffraction was clear. Particle size distribution experiment indicated that the distribution diameter of NaGdF4:Eu nanoparticles was narrow.The prepared NaGdF4:Eu fluorescent nanoparticles had a good selective response to Cu2+, so it could be used as the Cu2+ probe for the quantitative detection. When the concentration of the NaGdF4:Eu nanoparticles was 1.0×10-3 mol·L-4, a good linearity between the fluorescence intensity and the concentration of Cu2+ in the range of 3.33×10-6-1.33×10-4 mol·L-1 was obtained. The linear regression equation wasΔI=3.828+0.676c with a correlation coefficient of 0.9984 and the detection limit was 8.9×10-7 mol·L-1. With the method the content of Cu in tea sample was determined and the results were in good agreement with those obtained with the atomic absorption spectrometry.The NaGdF4:Eu nanoparticles could couple with trypsin by electrostatic interaction and the best experimental conditions were discussed. At the same time, quenching mechanism of trypsin by the fluorescent nanoparticles was discussed. When the NaGdF:Eu fluorescent nanoparticles coupled with trypsin, the trypsin fluorescence had a certain quenching. A good linearity between the fluorescence quenching and the concentration of NaGdF4:Eu nanoparticles was obtained with a correlation coefficient of 0.9981 and the linear regression equation was 1=538.72-0.8412v. The quenching mechanism showed that it was a static quenching with the quenching constant Kq 6.74×1011 L·mol-1·s-1.