الفهرس 
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Abstract
The fluorescent carbon dots (CDs) have attracted great interest in the recent years in different fields such as bioimaging. The CDs fluorescent probes offer several advantages such as chemical stability, tunable optical properties, relatively low cost, simple preparation in addition to the great biocompatibility. In this thesis, fluorescent carbon dots were prepared adopting microwave-assisted solvothermal method using citric acid (CA) and ethylenediamine (EDA) as molecular precursors. The surface of the microwave-synthesized CDs was modified using two different passivation methods in order to tune their optical properties. The CDs were passivated by surface modification with polyethylene glycol (PEGylation) and by silica (SiO2) coating. The prepared different CDs were characterized by TEM, XRD, FTIR, UV-Vis absorption and emission spectroscopy. The spectroscopic studies revealed the enhancement effect of the surface modification on the fluorescence intensity and quantum yield of the prepared carbon dot. The surface modification with PEG resulted in superior improvement to the emission properties of the CDs with a 16٪ increase of the fluorescence intensity compared to as-prepared CDs. In order to investigate the biocompatibility of nanoparticles, sulphorhodamine-B (SRB) assay using HepG2 cell line was performed which indicate no toxic effect of CD and PEGylated CDs up to concentration 125 mg/ml after that cell viability decrease with increasing concentration while the SiO2-CDs didn’t show any toxic effect even at very high concentration 500 μg/ml. The confocal microscopic images of HepG2 cells after incubation with different concentration of carbon dot nanoparticles revealed that the cellular uptake of silica coated nanoparticles is more than that of as prepared carbon dot and carbon dot pegylated which indicate that the silica coating of CD is more convenient for bioimaging purpose.