Study On Synthesis Methods Of Ce, Tb Co-doped Lanthanum Fluoride Nanoparticles And Their Analytical Applications

Because rare earth has unique electronic structure, rare earth luminescent nanoparticles have optical properties, such as large Stokes shift, narrow half emission peaks, pure luminescent color, long luminescence lifetime, and so on. Rare earth luminescent nanoparticles have been successfully used in biological molecules determination, cell labeling, and immunoassays. As the research going, so far, it has received extensive attention of the researchers that how to one pot prepare nanoparticles which were uniform size, high crystallinity, good luminous performance and functionalized surface. This study attempts to one pot synthesize rare earth nanoparticles with good luminous performance, good water solublility and functionalized surface.With phosphoryl carboxylic acid copolymer (POCA) as complexing agent, phosphoryl carboxylic acid copolymer (POCA) modified LaF3:Ce,Tb (POCA-LaF3:Ce,Tb) nanoparticles were firstly one pot synthesized by hydrothermal method. The best conditions to synthesize nanoparticles which based on the luminescence intensity and water solublility of POCA-LaF3:Ce,Tb nanoparticles were as follows:the pH value of the reaction solution was 7.0, the volume of POCA whose mass fraction was 3% was 5.0 mL, the mole ratio of ammonium fluoride to rare earth ions was 4:1, the reaction temperature was 120℃, and the reaction time was 2 h. The luminescence intensity of the as-prepared nanoparticles were strong and stable and their lifetime was 4.47 ms. POCA-LaF3:Ce,Tb nanoparticles were characterized by many methods. The results showed that the as-prepared POCA-LaF3:Ce,Tb nanoparticles were hexagon with the average size of about 20 run, and the surface of the nanoparticles were successfully modified with POCA, which realized the goal of functionalizing the nanoparticles with carboxyl group.POCA modified LaF2:Ce,Tb (POCA-LaF2:Ce,Tb) nanoparticles were synthesized by solvothermal method with ethylene glycol as the sovlent. The best conditions to synthesize POCA-LaF2:Ce,Tb nanoparticles were as follows:the reaction temperature was 200℃, the reaction time was 2 h, the mole ration of ammonium fluoride to rare earth ions was 4.5:1, and the volume of POCA whose mass fraction was 30% was 0.5 mL. The as-prepared nanoparticles were strong and stable on the luminescence intensity and their lifetime was 5.75 ms. The characterization results indicated that the diameter of POCA-LaF2:Ce,Tb nanoparticles was about 5 nm and its surface was modified with POCA.Using POCA-LaF3:Ce,Tb nanoparticles as energy donor, rhodamine 6G (Rh6G) as acceptor, we built a new luminescent resonance energy transfer system. Under the optimum conditions, the luminescent intensity’s quenching of the system is proportional to the concentration of Rh6G in the range of 1.00×10-6～10.0×10-5mol/L with the detection limit of 3×10-8mol/L.Otherwise, we established a new-type "optical switch" of thrombin, in which thrombin aptamer modified POCA-LaF3:Ce,Tb nanoparticles acted as donor and tetramethyl rhodamine modified the complementary strand of thrombin aptamer acted as acceptor. The switch was sensitive to thrombin.