| Recently, bioimaging is considered as one kind of efficient method for reflecting cellular status vividly with the quick development of nanotechnology and biotechnology. Carbon quantum dots (CQDs), as novel fluorescent materials, are widely received as potential alternatives due to their prominent fluorescence, good stability, and easy surface modification feature, especially the exceptional biocompatibility. However, investigations on preparation methods and characterizations are still in the elementary period, and issues on fluorescent mechanism are not well-acknowledged widely. Most of current CQDs preparation methods are inherited from traditional semi-conductor materials or other carbon nanomaterials. Choosing proper raw materials and simplifying preparation methods are the main research topics. The thesis aims to establish flexible preparing roadmaps based on chemical cutting. Furthermore, effects of environment factors on properties and applications in cellular imaging are also investigated.Details are including as following four parts:1) Carbonized walnut shells with carbon content more than 80% and relatively complete carbon network were developed, which could be used as novel carbon source materials for fabricating CQDs. We used waste walnut shells as raw material and obtained porous carbonized walnut shells which possessed high carbon content up to 84% and relatively complete carbon network. Micro-structure revolution in one-step carbonization was analyzed.2) Fluorescent walnut shells based CQDs were successfully achieved by chemical cutting method. Walnut shells based CQDs exhibited good stability and prominent up-conversion. The average diameter was below 5 nm, and lattice fingers could be obviously observed by high-resolution transmission electron microscopy. The lattice distance was 0.258 nm, corresponding with the (102) space of sp2 carbon in graphite-like structure. Walnut shells based CQDs possessed zigzag and armchair edge structure. The edge structure, functional groups as well as inside structure defects were considered to be beneficial to their fluorescent effect according to the surface defect theory.3) Disciplines of influences of environment factors on CQDs’ fluorescence were investigated, which offered support for preparing controllable walnut shells based CQDs. Increasing oxidation cutting temperature induced photoluminescent emission peak blue shift; the addition of deionized water during dilution could be considered as a kind of "trigger switch" for activating the fluorescence in walnut shells based CQDs; repelling and attracting of surface charges at different pH conditions led to scattering and gathering of nanoparticles respectively, finally resulting in the fluorescent intensity changing; adding alcohol decreased the fluorescent intensity; both the influences of pH conditions and alcohol were reversible, which could be ascribed to the reversible conversion between formation and breaking of functional groups.4) Raman imaging technique was firstly and successfully applied in investigating CQDs distribution inside cells. Good biocompatibility and bioimaging results of walnut shells based CQDs were proved firstly. The particular was that walnut shells based CQDs showed some side effects on osteosarcoma MG-63 cells proliferation due to the existence of singlet oxygen, which was significant for achieving target treatment in the future. Creatively, Raman imaging technique was applied in detecting CQDs distribution inside cells. The interaction between cells and CQDs was explained well here.A novel chemical cutting preparation method is designed to harvest nano-sized, stable and fluorescent walnut shells based CQDs from carbonized walnut shells. Based on their positive evaluations on biocompatibility, Raman imaging technique is firstly introduced to explain the process of CQDs entering into cells, laying a basis for developing further applications of walnut shells based CQDs in bioimaging and disease diagnosing. |
PDF Full Text Request