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Abstract
This thesis is aimed to prepare N-GQDs and CIS/ZnS QDs. The QDs will be inv by FTIR, Raman spectroscopies, XRD, HRTEM and Zeta potential.
NG/CIS/ZnS QDs nanocomposite will be synthesized with different conditions concentration ratios, pH and reaction times. These nanocomposites will be investigated to optimum conditions according to their performance using UV-Vis and PL spectroscop’ less cost and simpler biosensor based on NG/CIS/ZnS QDs nanocomposites for dj enzymatic, non-enzymatic cholesterol and AA are the main target with different concer pH and incubation time. Limit of detection, sensitivity and selectivity in the presence of interfering bionanalyte of the NG/CIS/ZnS QDs are determined and investigated.
Quantum dots (QDs) are special types of groups 1II-V, 11-VI, IV and 1V-VI semiconductors crystals which the size is ranging from 2 to 10 nm. They can be categorized into two groups. One is the self-assembled QDs which are grown epitaxially on the semiconductor substrate, and another one is the colloidal prepared in the solvent using different chemical techniques. The emission wavelength of different QDs covers wide range of spectra from visible to infrared ll}.
1.1.1. History of semiconductor quantum dots
Nanocrystals of copper chloride in a molten glass matrix was synthesized by Russian physicist Alexei Ekimov at the end of the 1970s. He then observed fluorescence and a gradient change of colors. These observations were published in 1980 (2).
In 1982 the first theory aiming at explaining the behavior of these very small crystals by the confinement of their electrons was published by another Russian physicist, Alexander Efros. Followed by Alexei Ekimov, the American scientist Louis Brus successfully synthesized nanocrystals in a liquid form, to obtain a colloidal suspension. He synthesized the first colloidal cadmium sulphide (CdS) quantum dots and published his results in 1983 (3). In 1987, the first lithographic QDs was synthesized by Mark A. Reed and in the energy levels of QDs and quantization of energy charge were discovered by MIT groups in the delft university (4). During the period of 1990-1993, a new synthesis method ”metal organic -coordinating solvent -high temperature” was first used by researchers in Bell Lab of US. They achieved the synthesis of high quality CdSe nanocrystals by using dimethylcadmium (CdMe2) at a high temperature of 300 °C (5). The beginning of 21st century, Prof. Xiao gang Peng invented a ”Green Synthesis” method to.