Abstract
M.Sc. (Nanoscience)
One of the parameters that cause cardiovascular diseases (CVDs) is high level of cholesterol in the blood. Therefore, monitoring of cholesterol level is of great importance, especially to elderly people and people with high risk of such diseases. This work explores the applicability of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) in developing a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The as-synthesized mercaptopropionic acid (MPA) capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), powdered X-ray diffraction (XRD), fourier transform infrared (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima red-shifted as the reaction time and shell growth increased. The increase in PL intensities shows proper passivation of the QDs surface with PL quantum yield (PLQY) of 33.8 %, 69.2 % and 57 %, for CdTe, CdTe/CdSe and CdTe/CdSe/ZnSe QDs respectively. The XRD patterns of all the as-synthesized QDs consist of three diffraction peaks corresponding to (111), (220) and (311) cubic zinc blended structures. The estimated particle size of CdTe/CdSe/ZnSe QDs from XRD and TEM are 4.32 and 4.08 nm, respectively while the EDX confirmed the presence of corresponding elements. For biosensor design, PPI dendrimer was electrochemically deposited on glassy carbon electrode (GCE) and characterized using cyclic voltammetry (CV) and impedance spectroscopy (EIS) in both phosphate buffer solution (PBS) and ferricyanide solution ([Fe(CN)6]-3/-4) This was followed by drop-drying the QDs on the electrode to form GCE/PPI/QDs. Finally, cholesterol oxidase (ChOx) was drop-dried on the GCE/PPI/QDs electrode to produce GCE/PPI/QDs/ChOx-based electrochemical cholesterol biosensor. Scanning electron microscopy (SEM) was used to characterize screen printed carbon electrode (SPCE) as it was modified with different materials and was able to capture the nano-globular morphology of PPI dendrimer. The GCE/PPI/QDs/ChOx based cholesterol biosensor was able to detect cholesterol in the range 0.1-10 mM with a...