SiO₂ Nanowires Self-Assemble By Dielectrophoresis And Properties Characterization

Recent years, nanowires play important roles in biological/chemical detection and biological sensing. Therefore, the synthesis of nanowires has drawn more and more attention to many research groups. Recently, our group successfully achieved accurate controllable SiO₂ nanowires self-assembled in microelectrode. However, this method has certain limitations in biosensing application. It is very useful for realization of SiO₂ nanowires for the application in the biosensing if the SiO₂ nanowires can be self-assembled in microfluidic chip. Thus, the controllable and reversible self assembly of SiO₂ nanowires structure in microfluidic chip has been performed in the thesis under different condition. Subsquently, the structures stability and impedance properties of the self-assembled SiO₂ nanowires in different solution has been further investigated. Main works of this thesis include the following two aspects:1. Research on SiO₂ nanoparticles self-assembly behavior in microfluidic chips by dielectrophoresis.Based on the previous work of our group, the SiO₂ nanoparticles self-assembly behavior in microfluidic chips has been investigated. By changing the environment and electric-field conditions, the controllable SiO₂ nanowire structure was successfully self-assembled in microfuidic chip by using CH3HPO2-SiNPs nanopardicles. The factors that we studied for the self-assembly include velocity of microfluidics, frequency and voltage of AC field, and dispersion medium of CH3HPO2-SiNPs nanoparticles. This research work improves the method of nanowires self-assembly by dielectrophoretic （DEP）, which is hopfully to be used in biosensing field.2. Research on the properties of self-assembled SiO₂ nanowire structure by DEPBased on the research of Chapter 1, the properties of self-assembled SiO₂ nanowire structures in microfluidic chip by DEP was further investigated in this chapter. We mainly studied the stability and impedance properties of nanowire structures in different solution. The effects of ion species, ionic strength and solution pH on the stability and impedance properties of nanowire structures have been investigated, respectively. To the ion species, we first studied the stability and impedance properties of nanowire structure in NaCl solution. The result showed the nanowire structure is stable in this solution and its impedance properties has no significant changes by compared with that of in the pure water solution. We then use NaCl solution as control group, the properties of assembled nanowire structure in KCl; MgCl2 and PBS solution was studied. It was indicated that the nanowire structure is also stable in various ionic solutions and its impedance properties remains unchanged. The study of different ionic strength showed that this wire structure is able to remain stable in a certain ionic strength range, exclusively high ionic strength will damage its structure. The study of solution pH showed that this wire structure’s impedance increase as solution pH increase, this wire structure has excellent pH response. These results would provide a certain guide for the subsequent application of the nanowire structure.