الفهرس 
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Abstract
The early diagnosis of cancer is a key factor for its effective treatment. Therefore, it is very important to develop a new technology for early diagnosis and tracking the therapeutic responses. Carbon quantum dots (C-Dots) consider to be very promising candidate for biomedical imaging, because of their unique photophysical (properties (such as; tunable emission wavelengths, large molar extinction coefficient and quantum efficiencies), good biocompatibility, low toxicity and their low cost compared to the conventionally used organic dyes and semiconductor quantum dots (SQDs). This thesis is devoted to prepare carbon dots using different synthetic methods and study their photophysical properties such as optical absorptivity, quantum yield (QY) and radiative lifetime. Furthermore, the structural properties have been investigated via transmission electron microscope (TEM) and x-ray diffraction (XRD). Novel composites of C-Dots with the plasmonic particles such as gold and silver nanoparticles have been prepared. The influence of the plasmonic on the spectroscopic properties of the C-Dots has been investigated either in presence or in absence of dielectric polymeric spacer. A remarkable enhancement in the optical parameters such as absorptivity and the rate of electron-hole recombination has been observed for the hybrid nanostructure compared to pure carbon dots. In addition, these hybrid nanocomposites showed a higher QY than that of pure C-Dots (~ 22%). The QY was determined to be ~ 65 or 81% in case of C-Dots/Au and C-Dots/Ag , respectively. This enhancement is due to enhancing the incident excitation field via localized surface Plasmon in the metallic part, which leads to increasing the exciton radiative recombination rate in the carbon dots. This plasmonic enhancement was more pronounced in case of C-Dots/Ag nano-hybrid than that of C-Dots/Au hybrid because of the low intrinsic loss and the degree of the overlap between the absorption spectra of silver nanoparticles and carbon dots. Finally; In-vitro assay, all investigated materials did not reveal any cytotoxic effect using cytotoxicity colorimetric screening assay and in-vivo assay showed that carbon dots did not reveal any toxic effect.