The Synthesis And Application Of Nanoprobe Based Rare-earth Upconversion Nanoparticles

Rare earth upconversion nanoparticle is one of the most important rare earthluminescent materials. Over the last decades, more and more researchers pay theirattention to the study of rare earth upconversion nanoparticles and some greatachievements have been made concerning the synthesis and preparation ofupconversion nanoparticles, the biodetection and imaging, solar cell, and securitylabels so on and so forth. The luminescent property of the rare earth upconversionnanoparticles is very unique, which could absorb two or more low energy photons andconvert a high energy photon, that is, the wavelength of emission light is shorter thanthe wavelength of excitation light and thus it belongs to anti-stokes luminescence.Rare earth upconversion nanoparticles have a series of advantages, such as chemicaland optical stablility, and low toxicity. Also, they could adjust and control theemission situation of the upconversion nanoparticles by changing the doping cationsof the nanoparticles and further realize the same excitation with different emissions.Since the emission peak is quite narrow, the disturbance between the emission peaksis also quite small. Due to the use of980nm near-infrared excitation light as the lightsource, the background of biological samples is low and the damages to biologicalsamples are quite small and the depth of tissue penetration would be quite large.Vitamin C is one of the most important hydro-soluble vitamins, which wasalso called ascorbic acid due to the treatment of scurvy. Vitamin C plays vitalphysiological roles on human body, which could strengthen the flexibility of vessels,slow down the progress of atherosclerosis and prevent the elevation of blood pressureso as to reduce the risk of cardiovascular and cerebrovascular diseases. Vitamin Cmay improve immunity, participate in detoxification reactions and preventantihistamine and the synthesis of carcinogen. Vitamin C could serve as a cofactorfor different enzymes to participate the metabolism of amino acids and the synthesisof neurotransmitters, collagen and intercellular substance. Vitamin C may be anelectron donor in many intracellular and extracellular reactions owing to its redox potential, which might act as an antioxidant to regulate gene expression, regulatemRNA translation, prevent oxidant damage to intracellular proteins or resist agingand cancer. However, Vitamin C was converted from glucose in most of animals buthuman body couldn’t synthesize vitamin C due to the severe mutations ofL-gulonolactone oxidase gene, which prevented the synthesis of L-gulonolactoneoxidase. Therefore, people should obtain Vitamin C from food to keep thephysiological balance. Vitamin C is abundant in fresh fruits and vegetables, so it isimportant to detect Vitamin C in them.The main content of the thesis includes the following three parts:The first part of the thesis gives a comprehensive introduction to thedevelopment process of the upconversion nanoparticles from six perspectivesincluding the composition, the luminescence mechanism, the synthesis methods, themethods of luminescence enhancement, surface functionalization and application ofthe rare earth upconversion nanoparticles.The second part: such rare earth upcoversion nanoparticles as NaYF4: Yb, Er,NaYF4: Yb, Tm and NaYF4: Yb, Ho are synthesized by solvothermal method in thispart. Also the nanoparticles were characterized by TEM and fluorescence and theluminescence mechanism was discussed. Moreover, Er-Tm co-doped upconversionnanoparticles were synthesized with different doped ratios of Er and Tm. The tune ofthe emission intensity of the different emission peaks was achieved and themechanism was discussed.The third part: the nanoprobe based on rare earth upconversion nanoparticleswas designed and synthesized to detect the Vitamin C in biological samples. Thedesign principle of the nanoprobe is as follows: the ultraviolet absorption spectrumof the cobalt oxyhydroxide is broad and can be used as the quencher of theupconversion nanoparticles. When the CoOOH is modified on the surface of theUCPs, the luminescence of the UCPs can be efficiently quenched by the CoOOH. Inthe presence of AA, CoOOH was reduced to Co2+and the luminescence of UCPs canbe restored so as to achieve the aim of detecting Vitamin C. The light stability of thenanoprobe is very good and can react transiently. Also the adoption of980nmnear-infrared light as the excitation light source for the detection of Vitamin C inbiological samples could reduce the biological background and thus increase thesensitivity of the detection.