Dielectrophoretic Assembly Of Functionalized Silica Nanoparticles And Its Effects On Dielectric Properties Of Cells

Precise fabrication of controllable and reversible nanostructures or microstructures-based functional devices and systems are of great interest for expanding the potential nanotechnology applications in the areas such as biosensing. Dielectrophoresis (DEP), the movement of polarizable particle induced by a nonhomogeneous AC electric field, has been proven as a robust method to rapidly manipulate and assemble biological and synthetic nanomaterials into nanodevices and mocrosystems. However, due to inadequate understanding of DEP mechanisms, it remains very limited to precisely control the final structure of assembled nanoparticles under DEP. This thesis is aimed at DEP assembly of functionalized silica nanoparticles and its effects on dielectric properties of cells. Precisely controllable and reversible DEP assembled submicrostruct have been achieved by modification of anionic groups on silica nanoparticles, and the effects of intracellular functionalized silica nanoparticles on dielectric properties of cells have been proven. This thesis is composed of the following three parts:1. Research on effects of different surface functionalized groups on DEP assembly behavior of silica nanoparticles.The DEP assembly behavior of five types of silica nanoparticles (SiNPs), including OH-SiNPs, COOH-SiNPs, NH2-SiNPs, CH3HPO2-SiNPs and PEG-SiNPs have been investigated respectively. It was found that anionic groups could obviously enhance the DEP assembly behavior of SiNPs on the microelectrodes. The anionic group could bring an increase on the dielectric conductivity of the SiNPs by enhancing the surface conductivity. These results well indicated that the DEP assembly behavior of nanomaterials in aqueous suspensions could been changed by functionalized group modification.2. Research on controllable and reversible submicrowires assembled from CH3HPO2-SiNPs.On basis of the work in the first part, the DEP assembly behavior of CH3HPO2-SiNPs was further investigated. By using Rubpy dye doped in the core of the CH3HPO2-SiNPs, the assembly process was visualized real time by inverse fluorescence microscopy. Precise control over the frequency of the applied AC field showed that DEP forces can assemble CH3HPO2-SiNPs from aqueous suspensions into submicrowires and the number of the assembled submicrowires between microelectrode gaps could be well controlled with reversibility. Furthermore, the DEP assembly process of CH3HPO2-SiNPs is sensitive to pH of the dispersed medium. These findings provide a way to solve the difficulty in controlling the DEP assembly process of nanoparticles and offer application opportunities for DEP assembly of functionalized SiNPs.3. Research on the effects of different functionalized silica nanoparticles on dielectric properties of cellsElectrode arrays with different gap distances were designed to assemble cells with different dielectric properties into different region of the electrode arrays. The assembly behavior of Hela cells on the electrode arrays were investigated after incubated with different functionalized silica nanoparticles. It was found the intracellular functionalized silica nanoparticles could obviously change the assembled region of HeLa cells on the electrode arrays, which means the dielectric properties of the cells had been changed. This part of work provides a new method for investigating small dielectric property changes of cells.