Synthesis Of NaLuF₄:Yb,Er Up-conversion Nanoparticles And Their Immunolabelling To HeLa Cells

Up-conversion luminescence material is a kind of anti-Stokes luminescence materials, which could emit continuously shorter wavelength light under being excited by long wavelength light. Rare earth up-conversion luminescence material absorbs infrared light and could emit ultraviolet, visible or near infrared light. Because infrared exciting light could penetrate into biological tissue deeper and could not make the detected biological objects emit fluorescence, study on up-conversion luminescence nano materials and their application in biological analysis has attracted great attention by researchers. In the literatures of rare earth up-conversion luminescence nano materials, NaYF4 is used as host material commonly. But according to the latest reports, the up-conversion materials have better luminescent properties when NaLuF4 is used as host materials. In view of this, our reserch attempts to synthesize rare earth up-conversion nanoparticles with high luminescence intensity and good biocompatibility by using NaLuF4 as the substrate.In this paper, NaLuF4:Yb,Er nanoparticles were synthesized by solvothermal method with water-ethanol-oleic acid as the solvent and rare earth stearate as the precursor. The synthesis conditions were optimized based on the luminescence intensity of NaLuF4:Yb,Er nanoparticles, and the results were as follows:the reaction temperature was 160℃, the reaction time was 20 h, the mole ratio of fluoride to rare earth ion was 5:1, the mole ratio of sodium ions to rare earth ions was 2:1, the pH value of the reaction solution was 6.0, the volume of oleic acid was 5 mL, the contents of Er3+ and Yb3+ were 2% and 20% respectively. The luminescen properties of the nanoparticles prepared under the optimized conditions were good. The luminescence spectra demonstrated that the maximum emission peak was at 542 nm.The as-prepared NaLuF4:Yb,Er nanoparticles were characterized by many methods. The XRD pattern showed that the particles were hexagon and cubic crystals, TEM image indicated that the particles were spherical with the average size of 30～50 nm and FL-IR demonstrated the particles was coated with oleic acid.In order to improve the water solubility and biocompatibility, NaLuF4:Yb,Er nanoparticles were modified by amino. After modified NaLuF4:Yb,Er nanoparticles were characterized, and the results showed that NaLuF4:Yb,Er nanoparticles were successfully modified by amino group and their average size was 50～70 nm.In the presence of EDC and NHSS, rabbit anti-CEA antibody were covalently coupled with amino modified NaLuF4:Yb,Er nanoparticles. Based on the specific recognization between rabbit anti-CEA antibody and carcinoembryonic (CEA) antigen expressed on the HeLa cells, the HeLa cells were successfully immunolabelled and imaged with NaLuF4:Yb,Er nanoparticles.