الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
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Abstract
Biosensors combining biological and physicochemical, have great implications in healthcare, food, agricultural, and biodefence systems. Fluorescence-based biosensors have been entered into recently for efficient sensing of a range of bio-analytes. Carbon quantum dots (CQDs) are small fluorescent carbon nanoparticles with sizes less than 10 nm in diameter.
This thesis aims to prepare CQDs via pyrolysis of citric acid and glycine at 150 0C. This QD is investigated to be used as a biosensor for non-enzymatic detection of cholesterol and the sensitivity towards the cholesterol is evaluated. Cholesterol is a crucial lipid for the human body and a crucial structural element of the membranes of all animal cells. When the cholesterol level of the human body rises, both cholesterol and other lipids accumulate on the internal walls of blood vessels, leading to the formation of a thick waxy layer in the blood vessels, resulting in the development of atherosclerosis disease. Therefore, the preparation of a biological sensor is inexpensive, non-toxic, and available in an effortless way to detect cholesterol levels in the field of health care applications.
The prepared carbon quantum dots were characterized with different techniques such as UV-visible, Fourier Transform Infrared (FTIR), X-ray diffraction (XRD, Raman spectrum, photoluminance (PL) spectroscopies, transmission electron microscopy (TEM), and Zeta measurement.
By studying the effect of pH on the CQDs, it was found that the PL is pH dependent, a gradual increase in the acidic media from pH 3 to pH 6 happens and attains the highest PL emission in the neutral medium at pH 7 which is suitable for applying CQDs as a biosensor.
The PL of the prepared CQDs was investigated, and the PL of these CQDs was found to be excitation-independent PL emission with an emission peak was at 425 nm, and the highest PL intensity was attained at excitation of 350 nm. The ability of prepared CQDs to emit PL (Quantum Yield) has been measured in comparison with quinine sulfate as a reference. The quantum yield of CQDs was found to be high, benefiting the use of these CQDs as a biosensor.
In this thesis, CQDs were used as a biosensor to detect different concentrations of cholesterol at a low concentration in the mM. The results showed two linear relationships in a range of concentrations from 0.312 to 5 mM, (0.3-0.8 mM), (R2 = 0.8586) and in range of (1-5 mM), (R2= 0.9786) which is equivalent to the normal cholesterol range in the human body.
The selectivity of CQDs towards cholesterol was evaluated and showed a good affinity towards cholesterol in presence of different interfering materials with a concentration of 2 mM. This thesis is a practical application for using a type of quantum dots in an easy, simple, and inexpensive way as a biosensor for a biomolecule that is essential to the human body as cholesterol.