Synthesis And Characterization Of Quantum Dots In Aqueous Solution

IntroductionSemiconductor nanocrystals also known as quantum dots(QDs) have attracted considerable interests in biological,analytical scinence and medical field because of their unique size-dependent optical and electronic properties.As fluorescent probes,the optical properties of QDs presentoutstanding advantages over traditional organic dye molecules which used in fluorescence analysis.The excitation spectra of high-quality QDs are broad and successive,while the emission spectra are narrow and symmetric, which provides a possibility to develop multiplexed detection schemes,allowing excitation of multiple fluorophores with a single light source.QDs also have high fluorescence lifetime and high quantum yield,which can observe tagged target for a long time.Labeling and detecting the biomolecules with QDs have been a new and pop research field in biochemical analysis.However,luminescent QDs are commonly prepared by orgnometallic procedure and not compatible with aqueous assay conditions.Consequently,it is necessary to substitute the surface organic ligands with hydrophilic capping agents for biological applications.But for these methods,the conditions of preparation of QDs were relatively critical,and process was complicated.In contrast,the synthesis method of QDs in an aqueous medium using thiols as stabilizing agents is of simplicity,low toxicity and low cost.Most important is that the stability of QDs synthesized by aqueous approach is better than that of the water-soluble QDs transformed from organic solvent. Materirals and methodsThis thesis has synthesized water consistency CdSe,CdTe quantum dots in the aerobic and anaerobic conditions,and outsourcing in the nuclear shell by different components,focus on the reaction time,the optimal dosage,the ratio of reactants, reaction temperature,pH,coating time of reaction conditions on particle size of the quantum dots,fluorescence absorption and emission spectra,as well as the impact of quantum yield.Using UV spectrophotometer,fluorescence spectrophotometer, transmission electron microscopy,microplate reader,particle size analyzer, fluorescence confocal microscopy,fluorescence confocal scanner means for the synthesis of quantum dots were characterized.Results1.At aerobic conditions,the mercaptoacetic acid as modifier,was synthesized in aqueous solution and stable quantum dots CdSe/SiO₂ to study the various factors (reaction temperature,reaction time,the optimal dosage,pH,coating time etc.) on the quantum dot size,fluorescence absorption and emission spectra,as well as the impact of quantum yield.2.In anaerobic conditions,the mercaptoacetic acid as a modifier in the aqueous CdTe quantum dots were synthesized to study the reaction time,reaction temperature, the optimum dosage,pH value,such as the impact of quantum dots.Discusion1.At aerobic conditions,the mercaptoacetic acid as the modifier in the aqueous synthesis of quantum dots CdSe/SiO₂,uniform particle size,are spherical,with the reaction time and the package was different times,change size,fluorescence emission spectra also change in response time through the implementation and coating time on the quantum dot size the role of the tuner.2.In anaerobic conditions,the mercaptoacetic acid as a modifier in the aqueous synthesis of CdTe quantum dots,fluorescence excitation spectra of broad,sharp emission spectra,high quantum yield,fluorescence intensity,and the implementation by changing the reaction time and the ratio of reactants to tuning the size of quantum dots.