Preparation Of Upconversion NaYF₄:Yb³⁺/Er³⁺ Nanocrystals And Its Application In Bioprobe

Rare-earth upconversion nanoparticles (UCNPs) have the advantages of high chemical stability, strong optical stability, sharp emission bandwidths, low toxicity, long emission lifetime and large anti-Stokes shift. In addition, using the near-infrared laser as its exciting light makes it with the characteristics of deeper light-penetration depth, no photo damage to the living organisms and no background fluorescence, etc. These advantages make the UNCPSs have profound significance in the biological field. In recent years, the UCNPs have been successfully applied in biological cell imaging, disease diagnoses, drug delivery, gene therapy and DNA testing. Because the Y3+level of NaYF4 matches well with the photon energy of exciting light and the matrix is of low phonon energy, which reduces the loss of nonradiative transition, thus NaYF4 has become one of the hottest rare-earth upconversion matrix. This thesis had prepared NaYF4:Yb3+/Er3+ nanocrystals with various morphology through different synthesis methods. The growth mechanism of UCNPs was explored according to the influence of different experimental conditions. Then surface functionalized modifications were used to the UCNPs with good quality after building a new method of bioprobe sensor. Finally the bioprobe was applied in detection of miRNA in breast cancer cells. The thesis includes main contents as follows.The first section:various UCNPs with different crystalline (cubic and hexagonal phase) were synthesized by hydrothermal methods, and micro/nanocrystals with different size and morphology (nanospheres, nanorods, nanopillars, nanoplates ect.) were obtained by changing the reacting condition, the effects of synthesis conditions (temperature, reaction time, complexing agents, dissolvent ect.) on the crystalline, morphology and luminescence intensity were investigated. The results indicate that the crystal phase of the nanoparticles changes from cubic to hexagonal after raising the temperature and prolonging the reaction time.The second section:the NaYF4:Yb3+/Er3+ upconversion nanocrystals with high fluorescence intensity were synthesized from the liquid system of hydrophobic oleic acid-octadecene by thermal decomposition method where the rate earth-earth stearates were used as precursor. And the nanocrystals are characterized by Transmission Electron Microscope (TEM), X-ray Powder Diffraction (XRD) and Fluorescence Spectrophotometer. It was demonstrated that the as-prepared nanocrystals were hexagonal phase, small size (<50 nm) and high fluorescence intensity, which were suitable for bioprobe materials.The third section:The surface functionalized modification methods were applied to modify the surfaces of the NaYF4:Yb3+/Er3+nanocrystals, which turned the hydrophobic nanocrystals to NaYF^ Yb3+/Er3+-COOH nanocrystals which make it has hydrophilic and good biological coupling ability. Finally, the modified NaYF4:Yb3+/Er3+-COOH nanocrystals were used as a new type of bioprobe and applied in detecting the miRNA of breast cancer. The test results show that the designed bioprobe is of high selectivity, good stability, highly sensitivity and can be ued to quantitative detection of mi-RNA-21.