Green Fabrication Of CdSe Quantum Dots Core-Shell Structural Materials Applied In Biophotonic Imaging

With the rapid development of nanotechnology, compared to the bulk materials, nanomaterials exhibit unique physical and chemical properties, and have attracted an extensive interest. The semiconductor quantum dots (QDs) show excellent luminescent properties, tunable with sizes, which have a very widespread potential application in fluorescent labeling, laser, LED, solar battery etc. The researches on quantum dots have become a frontline subject in the cross field of materials, optics and biology. In this thesis, we extended study of controllable synthesis of cadmium selenide (CdSe) in a novel "green" way, fabrication of various CdSe core-shell structural composite QDs and study of the basic applications of the those composite QDs with excellent fluorescent effect in biomedical labeling, imaging and DNA biosensors as a new type of fluorescent probes .The detail content is as follows:1. The new type of synthesis system (oleic acid-paraffin liquid) for fabricating size-controllable cadmium selenide QDs was studied in detail. Using this simple method, CdSe QDs could be obtained in a low cost route. The various synthesis conditions were further studied in detail and were optimized. The results revealed that QDs obtained from the new synthesis route were well monodispersed with uniform size, a wide excitation spectrum, and a narrow and symmetric emission spectrum. The fluorescence was quite stable, which could resist to photobleaching. Moreover, we also try to synthesize other II-VI semiconductor nanocrystals in this new route, and give a direct for synthesizing series of quantum dots.2. CdSe-SiO₂ core-shell structural QDs were fabricated through a microemulsion self-assembly method. Properties of such composite QDs were characterized in detail, and the results showed that uniform silica shells were formed on the surface of CdSe QDs to improve their water-solubility and reduce their toxicity. A blue shift of the fluorescent peak was observed in this experiment.3. CdSe-ZnS core-shell composite structural QDs were firstly synthesized in situ oleic acid-paraffin liquid system. The fluorescent effect was greatly enhanced by capping ZnS shell onto the CdSe QDs. Several possible mechanisms were illustrated.4. The multilayer CdSe core-ZnS shell-SiO₂ shell composite QDs were synthesized following the above microemulsion method and the in situ oleic acid-paraffin liquid system, which were utilized as fluorescent probes in a preliminary application of biophotonic imaging. The composite multilayer QDs were suitable for biological detection, and successfully labeled the HeLa cells in vitro by electrostatic attraction.5. A DNA sequence detection biosensor was built by the fluorescent quenching effect of QDs with gold nanoparticles. The sensitivity of the biosensor was discussed by different proportions of QDs dosage to the single strand DNA sequences. Silica micro-fluidic capillary was utilized as the DNA hybridization channel, by which the structure of the biosensor was simplified and the requirement for the sample concentration was lowered.