Preparation And Application Of Rare-earth Upconvertion Nanoparticles

Rare-earth up-converting nanophosphors(UCNPs) have many advantages, such as low toxicity, high chemical stability, excellent light stability, sharp emission bandwidths, large anti-Stokes shift and long luminescence lifetime. Besides, the UCNPs utilized the near infrared laser as excitation source also brought a lot of advantages, like deep light-penetration depth, almost no damage, no background fluorescence in biological tissue and so on. Therefore, UCNPs have great application prospects in biological field. This thesis was to prepare the water-soluble upconvertion nanoparticles (NaYF4、Yb3+, Er3+), which were modified with carboxyl groups on their surface. And based the as-prepared functional UCNPs, we design some biosensors for the detection of thrombin, carcinoembryonic antigen or other biological molecules. This paper includes four chapters.In the first chapter, a general introduction of UCNPs was made, including the definition, luminous mechanisms, synthesis, bioapplications and so on. The purpose and signification of this thesis were described.In the second chapter, we use the solvothermal method prepare the water-soluble UCNPs (NaYF4:Yb3+, Er3+), and some carboxyl groups were modified on the surface. We chose NaYF4 as substrate, ethylene glycol as asolvent,6-aminocaproic acid as modifier to prepared modified UCNPs. The as-prepared UCNPs has good dispersion in water, and the average particle diameter is about 10nm, so makes it is more suitable for biological detection.In the third chapter, based on the fluorescence resonance energy transfer and aptamer-identification technology, a biosensor was developed for the detection of carcinoembryonic antigen (CEA). In the biosensor, UCNPs were the energy donor, while AuNPs as energy acceptor. As the linker of sandwich-like complex, the CEA aptamer would bind to CEA and cause the collapse of sandwich-like complex, leading to the recovery of fluorescence. Due to the high affinity and specifity of aptamer, this system has great sensitivity and selectivity. The detection range of the biosensor is 0.05 ppb to 2 ppb, and the detection limit is 0.05 ppb.In the fourth chapter, a simpler aptamer-biosensor for thrombin detection has been designed. As the same, the sensors were based on the FRET between UCNPs (NaYF4:Yb3+、Er3+) and Au-NPs. First, the thrombin aptamer was modified on the surface of UCNPs. Au nanoparticles narrow the distance between UCNPs and Au nanoparticles by adsorbed the aptamers. When aptamers specifically bind to thrombin, it would lead no aptamers to adsorb on Au nanoparticles. So the distance between UCNPs and Au-NPs became longer and the UCNPs fluorescence recovery. Thrombin can be detected by the fluorescence recovery of UCNPs. Compared with the method described in chapter three, the present method is not only easy to operate, but also saving the amount of DNA. So that it can reduce the testing costs. The sensor has high sensitivity, and easy to manipulate, and the detection range of the biosensor is 0.5 nM to 20 nM with good reproducibility.