Synthesis Of Shell-core Quantum Dot And Its Application In Biology

Shell@core quantum dots (QDs) are the new powerful tool for nanobiophotonics as a kind of novel fluorescent label. And comparing with narrow excitation, broad emission and narrow Stokes shift of traditional organic dyes, they possess tunable fluorescence emission, high photostability and attractive spectrum with almost symmetrical narrow emission and broad excitation; and they are scores of times as bright as the organic dyes at least. Due to such optical properties, in these years more and more important results have been achieved in bio-imaging and assay such as cell labeling, biomolecular detection and immunoassay. Although the strategies of synthesizing shell@core QDs are more popular and employed widely in biomedical diagnosis, it is still of importance to synthesize inexpensive QDs with high quality for application in biology. This thesis mainly focuses on the design, synthesis, optical properties, surface chemistry, bioactivity and biological application of QDs. The main results are as the following:1. Synthesis of ZnS-capped CdSe QDs with different sizes is mainly investigated in the thesis. It's shown that the fluorescence emission peaks at 510~630nm are tuned by the amount of Se/TOP stoke solution and the time, and that the quantum yield of QDs is hanced after capping with ZnS monolayer. These researchs offers a powerful tool for biological diagnosis and bioimaging.2. Temperature-dependence of water-soluble QDs was investigated as well. The photoluminescence of water-soluble ZnS@CdSe shell@core quantum dots was found to be temperature-dependent: as temperature arising from 280 K to 351K, the photoluminescence declined with emission peak shifting towards the red at a rate of ~0.11 nm K-1. And the studies show that the photoluminescence of water-soluble ZnS@CdSe quantum dots with core capped by a thinner ZnS shell was more sensitive to temperature than that of ones with core capped by a thicker one. That is, with 50% decrement of the quantum yield the temperature of the former need to arise from 280 K to 295 K, while the latter required much higher temperature (315.6 K), which means that the integrality of shell coverage is a very important factor on temperature sensitivity to for the photoluminescence of water-soluble ZnS@CdSe quantum dots. Moreover, it was found that the water-soluble CdSe quantum dots with different core sizes, whose cores were capped by thicker ZnS shells, possess almost the same sensitivity to the temperature. All of the studies about photoluminescence temperature-dependence of water-soluble ZnS@CdSe shell@core quantum dots show indispensable proof for their applications in life science.3. Properties of water-soluble shell@core ZnS@CdSe QDs were investigated as well. And such QDs were respectively conjugated covalently to transferrin (Tf) and mouse anti-human CD71 monoclonal antibody (anti-CD71) by 1-ethyl-3- (3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC) and N-hydrocylsulfo-succinimide (Sulfo-NHS). Such conjugations were efficient and the conjugates remain mostly intact, which were verified by column filtration, SDS-PAGE electrophoresis, absorption and fluorescence spectra and circular dichroism spectrometry. Thus, these two kinds of quantum dot conjugates were used to recognize the tumour cells. Moreover, in order to avoid the pseudo positivity, adding FITC-labeling secondary antibody IgG followed this manipulation, and the results showed that as-prepared fluorescent quantum dot bioprobes are highly specific to tumour cells. In a word, this work is constructive to popularization and applications of quantum dots in life science.4. After the bioactive QD probes were obtained, the red quantum dots (λem=614nm) were conjugated with anti-CD71 and labeled HeLa cells successfully. Then green QDs (λem=544nm) labeling goat anti mouse IgG (IgG/QDs(g)) was added to bind labeled anti-CD71/QDs(g) on the cell surface by immunoreaction. As the collected fluorescence spectra shown, as time goes on, the"red"peak intensity at 614nm increased with"green"one decreasing at 544nm. The changes of the fluorescence emission lasted 4min. During this proceeding, the peak at 614nm increased 32% while the one at 544nm decreased 55% with the ratio of fluorescence intensity (I614nm:I544nm) increasing from 2.1 to 6.4. The results show that fluorescence resonance energy transfer (FRET) occurs between these two kinds of QDs on the HeLa cells. Therefore, the FRET based on multicolor QDs enhances the sensitivity and reliability for immunoassays of antigen/antibody, and presents a simple and reliable method for high specific identification of tumour cells.