Synthesis,Spectral Analysis Of NaYF₄ Upconversion Nanocrystals And CdSe/CdS Quantum Dots,and Built A FRET Structure

In recent years, with the rapid development of nanotechnology, functional fluorescence nano materials, with its unique optical properties, are gradually exposing huge potential in life science field. This is especially true when it is incorporated with FRET technology, which constructs FRET physical models and serves for researches of the distance between the molecules, nucleic acid detection, genomics, protein conformation, macromolecular interaction and etc. It becomes a powerful tool for exploring aspects of the structure and the microscopic life activity process.In many of the fluorescent nano materials, rare earth upconversion nanocrystal and quantum dot materials received much more attention. Rare earth upconversion nanocrystal is an anti Stokes fluorescent material which can emit visible light by infrared excitation, It has narrow emission spectrum line, high fluorescence signal-to-noise ratio and stable optical properties. These properties as well as many others are mainly due to the outside electronic shell protection, which guarantees that the internal part can realize a lot of 4f - 4f to energy transition. Quantum dots is a smaller fluorescence material with only a few nanometers. Because of quantum limit domain, the spectrum of the quantum dot will experience blue shift as the decrease of its size. It has a wide absorption band, so we can excite many kinds of quantum by the same excitation light source, i.e. optical adjustability and flexibility. Based on these good fluorescence properties, at present these two kinds of materials has become a hot topic.This thesis works on light-emitting principle and disadvantages of these two kinds of Materials. At first,PEI is used as a surfactant to prepare liquid phase NaYF₄: Yb³⁺/ Er³⁺ upconversion nanocrystal with the average size of 40nm by hydrothermal synthesis. The test indicates that the nanoparticles has an uniform morphology with a higher conversion efficiency on green light segment and amino groups on the surface. It can be well disolved in the water. Based on the relationships among different datas and light-emitting principle, there comes the description of the process of nanopartical growth. Next, using a slow-release method,CdS shell structure is successfully covered on CdSe quantum dots. Shown by the spectroscopy testing and stability testing, with the increase of shell thickness, the fluorescence intensity of quantum dot will first increases and then abate. The whole spectrum experiences redshift which reflects that the role of the shell structure played on the quantum dot has transferred from a protection in the beginning to a quench gradually in the end. Quantum dot covers the shell layer with an optimum thickness. It has a better light-proof and bleaching capability as well as a more stable optical property. At last, using a self-made NaYF₄: Yb³⁺ / Er³⁺ as energy source and CdSe/CdS core-shell quantum dots as receptors, by the heterogenious combination of antigen and antibody specificity, a FRET structure is then set up. The existence of the structure is demonstrated by the spectral analysis, also the fact that the fluorescent material which is discussed in this paper has stronger application ability.