The Synthesis And Appliction Of Functional Quantum Dots Base On The Microfluidic Technology

In recent years,under the rapiddevelopment of science and technology, the research targets scale down to smaller and smaller dimensions. A typical example is thatthe microfluidic technology provides the possibility for the experimental process and device to become miniaturized. The microfluidic chips(MF), also known as “Lab-on-a-chip(LOP)”, is one of typical applications of Micro-Electro-Mechanical Systems(MEMS) technology. Microfluidic chips are composed by micron channel, pumps, reactors, electrode and other functional unitsfabricated on substratesmade from quartz, silicon, glass or polymer, etc. Based on the related physical and chemical theories,the microfluidic chips couldrealize a series of functions including the reaction, purification, extraction, separationanddetectionof samples. Compared with the traditional experimental methods, the microfluidics methods have the advantages oflowvolume design, reduced reagents consumption, no gas pollution, fasteranalysis, high integration, high degree of automation and high efficiency, etc. Based on these advantages, microfluidics chips have become the forefront of the experimental analysis tools, which have been widely applied in physical, chemical and biological research and other fields.Applying microfluidics chips to synthesizenanomaterial is one of the important research directions. Quantum dots as a new type of semiconductor nanomaterial are a promising research tool in nanobiophotonics research. Quantum dots areregarded as fluorescent probes with widespread application prospects, for theyhave broader excitation spectra, narrower and tunable emission spectra, comparablequantum yield, superiorphotostability, high colloidal stability and easier accessibility for surface modification compared to the traditional organic fluorescent dye. However, in the traditional multi-step synthesis methods, the high reproducibility and good quality of quantum dots cannot be obtained easily for the following reasons: 1) the distribution of the ion concentration inreaction solution is uneven, 2) the mix efficiency of the solution is low, 3) the temperature in the reaction container is uneven and hard to control. To avoid such problems, this thesis presents the application of microfluidic chips on the synthesis of binary CdTe and ternary CuInS2 quantum dots. Through using microfluidic chips to well control the reaction temperature, concentration and the process of mixing, we obtained the quantum dots with better quality than those prepared using traditional methods. The subsequent surface modification using biomolecules realized the selective labelling of liver and pancreatic cancer in vitro and vivo. The main contents of this thesis are as follows: 1. Design and fabricate the microfluidic chips forsynthesis of the quantum dotsIn this thesis, a detailedstudy was performed on the microfluidic chips for synthesizing the quantum dotsfrom the aspects of design, simulation and fabrication. Firstly, an overview of the current development of microfluidic chips fabrication process is presented and the materialsused to fabricate the chips are compared from the aspect of advantages and disadvantages. Secondly, this thesis givesa detailed introduction of microfluidic theory in simulation study. Then COMSOL Multiphysics simulation software was appliedto performthe simulation studies, in which the variable parameters were adjusted fortheCdTe quantum dots synthesis process in the microfluidics channel. Thirdly, a detailed descriptionwas given on the fabrication process of microfluidic chips, and thisPDMS-based process was optimized to obtain the easy-to-make and high reusable microfluidic chips. 2. The synthesis of biofunctional CdTe QDs using microfluidic chips for biological applicationA “one-step” synthesis method using microfluidic chips was applied to synthesizeCdTe quantum dots with BSA(Bovine serum albumin) as the surface ligand. Firstly, we designed and optimized the parameters of microfluidic chips(eg. reaction temperature, the length and width of the channel) for fabricating the biomolecule-functionalized quantum dots applying the laminar model from COMSOL Multiphysics software. Secondly, the UV-VIS spectra, Photoluminescence spectra, Fourier transform infrared spectroscopy(FT-IR) spectra and Agarose gel electrophoresis results wereacquired to characterize the MF BSA-QDs and compare them with QDs synthesized usingthe traditional bench-top method. The results shows, BSA-QDs prepared using the microfluidic approach show significantly higher photostability, colloidal stability and protein functionalization efficiency. Then we used the same “one-step” synthesis method to fabricate the CdTe quantum dots with Folic acid(FA) biomolecule as the surface functionalized ligands. Finally, the BSA-QDs were employed for labeling RAW264.7 macrophages cell and the FA-QDs were used for labeling Panc-1 cells. We also used FA-QDs for the in vivo imaging of the tumor-bearing mice.The pathological analysis shows that this MF FA-QDs material did not affect the health of mice. 3. The application of biofunctional CuInS2 QDs synthesized using microfluidic chipsIn this thesis we first used the combined microfluidic chipsto synthesize CuInS2, CuInS2/ZnS and dBSA-CuInS2/ZnS quantum dotsusing“one-step” method. Then the specific biomolecules were selected to modify the surface of these quantum dots. The emission wavelength of dBSA-CuInS2/ZnS quantum dots located at the NIR range, suggesting that these QDs are appropriate for the bioimaging application. Through analyzing the characterization results of dBSA-CuInS2/ZnS QDs, we concluded that applying dBSA(denatured BSA) as the outermost layer stabilizer of the quantum dots can increase the quantum yield and the efficiency of bioconjugation. Here we introduced FA and Hyaluronic Acid(HA) as the surface modification biomolecule to functionalize the dBSA-CuInS2/ZnS QDs. Then the FA-QDs and HA-QDs were employed for labeling the Panc-1 pancreas and HepG2 liver cancer cell.The results showthat these QDs couldspecifically labeled the cancer cell. These above provide a theoretical and experimental foundation for the biofunctional QDs prepared using the microfluidic approach to use atthe clinical stage in the future.