| Double-strand DNA is a double-helical structure formed by two complementary single DNA through base pairing. DNA is a ideal material in nanotechnology for the construction of designed nanostructure and nanomachine, because DNA is easily obtained by chemical synthesis, its sequence and base number can be precisely controlled, and the size of base is small. The interaction of DNA and its analogue is widely researched recently for expanding the application of DNA. It is reported that various metal ions are able to react with nucleoside, for example, normally mismatched base pair T:T form a new metal-base pair T-Hg-T with the addition of Hg2+ ions, and C:C form metal base pair with Ag+ ions.DNA strand displacement reaction play an important role in non-enzymatic pure DNA reaction. We utilized the concept of metallo-toehold todevelop a new method of regulating the kinetics of DNA strand displacement reaction. C:C mismatched base pair was introduced on the toehold. Fluorescence spectrometer and non-denaturing PAGE was used for characterization. The rate of DNA strand displacement reaction was slow without Ag+, however the rate obviously increased with the addition of Ag+ ions. Through altering the concentration of Ag+, the rate of displacement reaction could be easily, sensitively and continuously tuned. The rate of displacement reaction first increased till maximum, and then decreased till the reaction barely occurred, because two many Ag+ ions presumably gathered round C base, impeding the information of normal base pair. This reaction system had excellent properties of high specificity and selectivity to metal ions. We could design special DNA segment to explore the specific reaction with other metal ions. It was also used to detect the metal ions. We hope this reaction system can be applied to DNA nanotechnology.The rate of DNA strand displacement reaction is closely related to the number of complementary base pair on the toehold. Based on the study above, two mismatched base pair T:T and C:C were introduced on the toehold, in other words, there were two regulating factors in the system. We carefully designed two sets of the length and sequence of the toehold. In one set of experiments, the displacement reaction occurred successfully only under the condition of simultaneously adding Hg2+ and Ag+ ions, that is, it was an AND gate. In another set of experiments, the displacement reaction occurred successfully under the condition of adding Hg2+ or Ag+ ions or both two ions, that is, it was an OR gate. So we had successfully constructed DNA molecular logic gate with the input of Hg2+ and Ag+ ions.Microfluidic chip is mainly applied to analytical chemistry and biological chemistry. The function of chemical reactions is integrated on the micro chip with the core structure of microchannel network. The micro chemical reaction is controlled in micron even nano scale. Therefore, the rate of reaction increase greatly, meanwhile the consumption of valuable samples reduce enormously, besides, the process of reaction will be greener and safer. The material of chip is the important foundation for fabricating chip, and glass and polymer is widely used recently. PDMS has been widely applied to produce microfluidic chips using molding with SU-8 photoresist. The method above has big advantage relatively, and the designability is strong, however the opration is complicated, and cost is high relatively.In this thesis, the simple glass mircofluidic chip was made of two coaxially aligned capillary tubes. The inner capillary tube is cylindrical with a tip tapered, and The outer capillary tube is square. The two coaxially aligned capillary tubes were fixed on a thick glass by epoxy glue. We had researched the process of droplet production with the chip above and the mechanism of the variation of droplet size under different erperimental conditions. The water and mineral oil were used as dispersed and continuous phase respectively. The rate of dispersed phase Qw (or continuous phase Qo) was fixed as a constant, and another increased gradually. We found three distinct classes of transition from dripping to jetting of droplet production in our experiment. Firstly, the shape and diameter of droplet was identical, which was dripping form of droplet, and then it decreased all the while till the droplet was hard to form at the end along with the increment of Qo when Qw was fixed at a low value, this was the first kind of transition form. Second, similarly, the shape and diameter of droplet was identical at the beginning, which was dripping form of droplet, the diameter of droplet began to reduce, then undergo a process of instability, and then increased slowly in the condition of fixing Qw at a high value with increasing Qo. This was a new interesting phenomenon and the second transition form. Finally, fixing Qo, the diameter of droplet increased all the time and a neck began to produce till spherical droplet was unable to produce, this was the third kind of transition. The statistics and analysis of the diameter and dispersity of droplet provided experimental data for how to obtain uniform droplet under different conditions. The experimental basis was provided for high-throughput producing uniform particle of polymer. |
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