| The microfluidic electrophoresis chip is an important part of micro total analysis systems (μTAS). They have some advantages including reduced reagent usage, decreased operation times and added capabilities, which was widely used in genome sequencing project, epidemic disease testing and drug screening. It has become a better research platform for the life science and chemical analysis field. But the injection and separation of samples in the conventional microfluidic electrophoresis chips system is to apply high voltage from several hundreds to thousand volts, there are some safety risks for operators and the large power equipment is difficult to integrate, which limit the microminiaturization and integration of chip system. Therefore, a proposal of developing the low voltage electrophoresis chip system has been given by some researches. However, this system is still in the stage of research, and there are several key techniques, which need to be solved before this kind chip is used for commercial purpose. They include the bubble issue, optimization of the chip structure, low cost of surface modification for the chip, manufacture of miniaturized control and detection system. To solve these problems, the research of key technologies for low voltage electrophoresis chip analysis system has been developed in this work.The principle based on the electrophoresis technique of sample driving for the low voltage electrophoresis chip is similar to the way of conventional electrophoresis chip, but the control mode is different. According to the theory of the conventional electrophoresis chip, the concept of the low voltage electrophoresis chip was proposed. The cross channel and helix channel low voltage electrophoresis chip were designed, and the finite element analysis software ANSOFT was using to simulate the potential and electric filed of the chips. The simulation result indicated the feasibility of the low voltage driving method. In addition, the parameters of the chip structure such as depth of the micro channel, the thickness of the insulation film, size and position of electrodes were optimized.The fabrication procedures for the low voltage electrophoresis chip were discussed in details. The arrayed Pt electrodes were deposited on a piece of glass by magnetron sputtering. The glass cover was using wet etching method. The PDMS cover was fabricated by mold replication technology, which using silicon and SU-8mold. By comparison, SU-8mold has the advantages of short cycle time manufacturing, high precision, vertical edge, which became the best choice. In order to eliminate bubbles in the channel of low voltage electrophoresis chip, the PDMS film and the silicon dioxide film as the insulation film were proposed deposited on the Pt electrodes. Simultaneously, the electrical and structural characteristics of the two kind films were investigated. SiO2film was deposited by electron-beam evaporation. Experiment results showed that the surface of SiO2film became smooth and uniform for the growth temperature at300℃, the breakdown electric field strength was500KV/cm and the breakdown voltage was200V for the thickness of the film at4μm. The breakdown strength and breakdown voltage of the PDMS film with the same thickness was560KV/cm and220V. The electric insulation property of the two films is close, but PDMS film has low cost and simple manufacturing process.PDMS is a hydrophobic material, which makes a difficult transferring sample solution in the channel of electrophoresis chips, so the PDMS is needed to improve the surface hydrophily for decreasing non-specific adsorption of hydrophobic. In this work, UV/ozone method was utilized to hydrophilize the surface of PDMS and compared to UV method. Contact angle measurements show that the hydrophilic of the PDMS sample by UV/ozone was significantly enhanced compared with UV method within the same time. The results of FTIR spectroscopy indicate that many chemical functional groups of PDMS surface have been changed by UV/ozone modification,-CH3hydrophobic group gradually decreased with the time,-OH and Si-OH hydrophilic groups increased obviously, and the characteristic peaks of SiO2gradually appear. XRD and SEM/EDS results show that the glass-like SiCO2layer formed on the PDMS surface. The hydrophilic groups and SiO2layer are the main reason for the enhancement of the PDMS hydrophilic. The experiment results demonstrate that the UV/ozone treatment was a simple operation and low cost hydrophilic modification method.The control system for the arrayed electrodes of the low voltage electrophoresis chip was present. This system consists of STM32chip, driver chip, optocouplers, the amplifier-filter circuit, D/A and A/D circuit which controlled the switch time, driving mode and voltage output of the arrayed electrodes. The fluorescence detection system was designed for the low voltage electrophoresis chip that included a main control FPGA chip, CCD sensor, laser light source and pre-processing circuits. With the application software of the host PC, the detection system could test the sample and realize the real-time display of the sample fluorescence spectra.The low voltage electrophoresis chip, control system, detection system constituted the whole sample analysis system. The Rhodamine B and Rhodamine6G as the sample were used in the electrophoresis separation experiments on the two kind low voltage electrophoresis chips. Test results show that the electrophoresis separation of the sample was achieved by applying voltage90V on the two chips. In addition, the helix channel chip has better separation than the cross channel chip, and the degree of separation for the low concentration sample was more than one. The sample can be successfully separated below the100V using the low voltage electrophoresis chip system in this work. Compare with the conventional electrophoresis chips system, the applied voltage declined an order of magnitude and the size became smaller. This work will lay the foundation for the further miniaturization, integration of the electrophoresis chip system. |
PDF Full Text Request