单细胞分析是生命科学和生物医学研究的基础，而细胞的分离与筛选是单细胞分析技术中一项基础工作，也是临床医学检验的重要内容之一。但如何在血液中连续、高效、高活性的分离出关键细胞已成为生物医学上亟需解决的重要问题。鉴于上述需求，在对目前国内外细胞分选技术分析比较的基础上，本论文确立了基于微流控技术的光纤光镊细胞分选方案。开展了单细胞流形成机理和细胞分选机理的理论、仿真及实验研究，提出一种易集成、高效、高活性的连续性细胞分选方法。论文主要包括以下几方面的内容： (1)建立了流体聚焦理论模型。要实现光纤光镊对细胞的高效分选，首先要形成单细胞流。流体聚焦方式包括电力聚焦和水力聚焦两种。目前国内外对水力聚焦的研究较多，对电力聚焦的研究较少。而且微通道几何形式不同，流动方式略有不同，因此多采用数值模拟方法来预测聚焦流宽度，还没有建立外加参数与聚焦流宽度的直接关系。本文从质量守恒定律出发，将海姆霍兹-斯姆鲁乔斯基公式和基尔霍夫定律相结合，建立了电力聚焦理论模型，推导出电力聚焦的中心流宽度公式，得出聚焦流宽度取决于入口电压比和通道几何尺寸参数。而在通道几何尺寸固定时，聚焦流宽度主要取决于入口电压比，入口电压比越大，聚焦流宽度越小。其后的仿真和实验结果与理论计算结果较为吻合，验证了公式的合理性。 (2)提出将水力聚焦和电力聚焦相结合的方式来形成单细胞流。在实验过程中发现，细胞在水力聚焦流和电力聚焦流中的运动形式不同。在水力聚焦流中，细胞运动杂乱无章。而在电力聚焦流中，细胞运动间隔较为一致，但较大的电压有可能造成细胞损伤。考虑到稳定的单细胞流是高效光镊分选的前提条件，且充分发挥两种聚焦方式的优点，将两种聚焦方式相结合，即复合聚焦来形成可控的单细胞流。用水力聚焦来控制细胞流宽度，较小的电力聚焦电压来控制细胞运动。实验证明在此种方式下所形成的聚焦流中细胞运动间距更加均匀一致。 (3)开展了平端面单模光纤对细胞的散射力的理论研究。深入研究了细胞在二维光阱和三维光阱中的受力机理，确定了以二维光阱中的散射力来驱动细胞进行分选。从光纤波动理论出发，以T矩阵算法推导出平端面光纤对细胞的散射力公式，得出细胞所受到的散射力主要取决于激光功率、细胞半径、辐射压力系数、细胞位置、束腰半径及波长。因此不同直径的细胞受到同一激光的散射力不同，可使细胞沿着激光光轴方向发生不同的偏移距离，从而进入不同的分选通道。并在其后的仿真和实验过程中，验证了不同参数对细胞偏移距离的影响。 (4)开发了光纤光镊细胞分选实验系统。经过反复实验，实现了单模光纤和微流控芯片的集成。在实验中对微流控芯片通道结构进行了优化，建立了扩张型十字通道，实现了酵母菌细胞和聚苯乙烯微球的连续性分选。实验证明，该系统分选效率可达92%以上，酵母菌细胞存活率可达90%。与其他分选系统相比，该分选系统无须标记，可实现细胞的活性连续性分选。 关键词：微流控芯片；细胞分离与筛选；光纤芯片；单细胞流；光散射力

 Single cell analysis is the basis of life sciences and biomedical research. Cell separation and screening is a very important basic procedure in single cell analysis technology, and it is also a basic and necessary daily operation procedure in biochemical tests. However, how to isolate key cells in blood continuously, efficiently and actively has become an important problem in biomedicine. In view of the above requirements, based on the analysis and comparison of cell sorting technologies at home and abroad, this paper has established a cell sorting scheme of optical tweezers based on microfluidic technology. The theory, simulation and experimental study on the formation mechanism of single cell flow and cell sorting mechanism are carried out.A continuous cell sorting method with easy integration, high efficiency and high activity was proposed. It mainly includes the following aspects: (1)A theoretical model of fluid focusing is established. In order to achieve efficient cell sorting by optical tweezers, the first step is to form a single cell flow. Fluid focusing includes electric focusing and hydraulic focusing. At present, there are more studies on the hydro-focusing at home and abroad, and less on the electric focusing. Because the geometry of microchannel is different and the flow pattern is slightly different, numerical simulation method is often used to predict the width of focusing flow, and the direct relationship between the external parameters and the width of focusing flow has not been established. Starting from the law of conservation of mass, combined with Helmholtz-Smoluchowski equation and Kirchhoff law, this paper establishes the theoretical model of electric focusing, deduces the central flow width formula of electric focusing, and concludes that the width of the focusing flow depends on the inlet voltage ratio and the geometric parameters of the channel. When the channel geometry is fixed, the width of the focusing flow mainly depends on the ratio of the inlet voltage. The larger the ratio of the inlet voltage, the smaller the width of the focusing flow. Thereafter, the simulation and experimental results are in good agreement with the theoretical results, which verifies the rationality of the formula. (2)The method of combining hydrodynamic focusing with electric focusing is proposed to form single cell flow. During the experiment,it was found that the cell's movement patterns were different in the hydrodynamic focusing flow and the electric focusing flow. In the hydrodynamic flow, the cell movement is disorderly. In the electric focusing flow, the cell movement interval is more consistent, but the higher voltage may cause cell damage. Considering that stable single cell flow is the precondition of high efficiency optical tweezers sorting, and giving full play to the advantages of the two focusing modes, the two focusing modes are combined. That is to say, compound focusing is used to form controllable single cell flow. The width of the cells flow is controlled by hydrodynamic focusing ,and the cell movement is controlled by smaller electric focusing voltage. Experiments show that the spacing of cell movement is more uniform and consistent in the focusing flow formed by this way. (3)The scattering force formula of flat-end single-mode optical fibers to cells is derived. The stress mechanism of cells in two-dimensional optical trap and three-dimensional optical trap is deeply studied, and the scattering force in two-dimensional optical trap is used for sorting cells. Based on the wave theory of optical fibers, the scattering force formula of flat-end optical fibers to cells is deduced by using T-matrix algorithm. It is concluded that the scattering force of cells mainly depends on the laser power, cell radius, radiation pressure coefficient, cell position, beam waist radius and wavelength. Therefore, the scattering force with the same laser for cells of different diameters are different,so that cells of different diameters can be separated by different offset distances along the direction of the laser optical axis, thereby entering different sorting channels.The effects of different parameters on cell migration distance were verified in the subsequent simulation and experiment. (4)An experimental system for cell sorting of optical tweezers is developed. After repeated experiments, the integration of single-mode optical fibers and microfluidic chips is realized. In the experiment, the channel structure of microfluidic chip was optimized, and the expanded cross channel was established to realize the continuous separation of yeast cells and polystyrene microspheres. Experiments show that the sorting efficiency of the system can reach more than 92% and the survival rate of yeast cells can reach 90%. Compared with other sorting systems, this sorting system does not need labeling and can achieve continuous sorting of cell activity. Key words: microfluidic chip; cell separation and screening; optical fiber chip ; single cell flow;light scattering