Synthesis Of Dipicolinic Acid Sensitized LaF₃:Tb Luminescent Nanoparticles And Their Application In Biological Analysis

Rare earth luminescent nanomaterials have been successfully used in biological molecules determination, immunoassays and cell labelling due to their unique optical and chemical properties, such as narrow half emission peaks, large Stokes shift, long fluorescence lifetime, low toxicity, high chemical stability, and so on. Now, the studies on the synthesis and biological application of rare earth luminescent nanoparticles have aroused widespread attention by scholars home and abroad.Here, the LaF3:Ce,Tb luminescent nanoparticles were firstly synthesized by hydrother-mal method, and the synthesis conditions were optimized based on the luminescence intensity and state of LaF3:Ce,Tb nanoparticles solution. The results showed that the best conditions to synthesize LaF3:Ce,Tb nanoparticles were as followed:the mole ration of sodium citrate to rare earth ion was0.6:1; the mole ration of ammonium fluoride to rare earth ion was4:1; the Tb3+and Ce3+doped content was10%and20%, respectively; the pH value of the reaction solution was7.0; the reaction temperature was120℃and the reaction time was4h.In order to further enhance the luminescence intensity of LaF3:Ce,Tb nanoparticles, dipicolinic acid (DPA) sensitized LaF3:Tb (DPA-LaF3:Tb) nanoparticles, which were obtained through replacing few sodium citrate on the surface of the nanoparticles by DPA, were synthesized. The effects of reaction conditions on luminescent performances of DPA-LaF3:Tb nanoparticles were also studied. The best reaction conditions were as followed:4.0mL2.0×10-2mol·L-1DPA solution was added into4.0mL4.2×10-2mol·L-1citrate coated LaF3:Tb nanoparticle solution; the pH value of the reaction solution was4.0; the mixed solution was kept oscillating at room temperature for five minutes. The lifetime of as-prepared DPA-LaF3:Tb nanoparticles was2.95ms.DPA-LaF3:Tb nanoparticles were characterized by many methods. The fluorescence spectra demonstrated that the excitation and emission peak were at272nm and546nm, respectively. The XRD pattern showed that the as-prepared DPA-LaF3:Tb particles were hexagon. The TEM image indicated that the nanoparticles were spherical with the average size of about15nm.Based on the luminescence quenching of DNA on DPA-LaF3:Tb nanoparticals, a new method for quantitative detection of DNA was established. Under the optimum conditions, the logarithm of the luminescent intensity of the nanoparticals is proportional to the concentration of DNA in the range of0.083～13μg·mL-1with the detection limit of0.02μg·mL-1. The established method was successfully to be applied to detect DNA in synthetic samples with the recoveries of95.6～104%, which indicated good accuracy was received.