Development And Application Of Rapid Mixer Based On Microfluidic Chip

Rapid mixing technique can provide an intimate contact between the reagent molecules for biological and chemical rections and has been widely applied in the study of biomolecular folding, enzyme assay, polymerization and synthesis of nanoparticals. As the development of microfluidics technology, the micromixers have gradually become one of the major rapid mixing methods. The mixing dead time has been reduced to the time scale of milliseconds or even microseconds by designing the channel geomtries or using external energy input. Micromixing has been a crucial process of micro total analysis systems and chemical synthesis, and various micromixers have been reported for specific applications in the past decade.Currently, microfluidic mixers have gotten significant improvements in reducing the mixing time and the sample consumption. However, it is still hard to mix high viscosity solutions in continuous-flow micromixers, difficult to find immiscible solutions in multiphase micromixers and complicated in fabrication of active micomixers, which restricted the further application of micromixer. For various applications in biology and chemistry, novel multiple mixers were highly deseired. In this thesis, we designed three unique micromixers for high viscosity solutions and segmented flow.Firstly, to mix high viscosity solutions, we designed a three-dimensional(3D) micromixer. The mixing domain of the mixer contained three consecutive subunits, each consisting of a “U”-type channel followed by a chamber with different width and height. Numerical simulations and experimental characterizations confirmed that the 3D micromixer could achieve a dead time of 122.4 ?s for mixing solutions of water and 80 % PEG200(viscosity 35.25 mPa?s). We found that the Dean flow caused two parallel fluid streams to switch position in the “U”-type channel, and then the solutions would undergo a further enhanced mixing in the following chamber because of simultaneous vortices expansions in both horizontal and vertical directions. With this 3D micromixer, we further observed the folding kinetics of human telomere G-quadruplex, and unravelled a new folding process under molecular crowding conditions within 550 ?s, and validated that deleting TT from the 5' of the sequence increased the folding rate in high viscosity solutions.Secondly, using PDMS surface modification method, we developed a steady gas-liquid segmented flow mixer. Three different dilute solutions were injected at the flow rate of 3 ?L/min by the syringe pump, and the nitrogen was supplied at a certain pressure by the pressure regulator. Bubbles were generated in the T-junction of the microchannel uniformly. The solutions were mixed in the winding microchannel in 1.71 ms by the recirculation of the liquid without dispersion. We further investigated the kinetic process of the chemiluminescence reaction at different concentrations of horseradish peroxidase. It demonstrated that gas-liquid segmented micromixer could also be served in quantitative analysis of biochemical reaction.Finally, to solve the problem that the bubble could not be securely trapped in the microchannel for acoustic micromixing, we further developed a gas-liquid segmented acoustic micromixer. The gas-liquid segmented acoustic micromixer device was fabricated by sound wave generation technique and the gas-liquid segmented generation technique. The piezo transducer driven by a function generator at a certain frequency was set up to produce the sound wave. Solutions of 90% glycerol were injected by the syringe pump at the flow rate of 0.5 ?L/min. By adjusting the pressure regulator, we found the mixing caused by the acoustic streaming of liquid /nitrogen interface in the T-junction, which has not been reported previously. In a higher gas input pressure, uniform gas-liquid segmented flow was generated, and the axial dispersion has been reduced. The steady gas-liquid segmented flow could be mixed in 96 ms by the acoustic streaming and recirculation of the liquid. In addition, the mixing efficiency as a function of applied frequency and voltage were analysed.In summary, we have demonstrated three unique rapid micromixers to solve the problem of the mixing in microchannel. These micromixers would be widely used in field of biochemical reactions.