Preparation Of Quantum Dots And Their Applications In Biological Labeling

The sensitive and selective detection of proteins,nucleic acid,peptides and other important biological molecules in organism or life process is an important field of life science. To explore and develop effective bio-analysis methods has been being the goal of analytical chemists.Fluorimetry is one kind of important methods for the life science studies,in which the detection sensitivity depends largely on their marker's luminous intensity and the photochemistry stability.Conventional organic dyes show some shortcomings such as narrower excitation and broader emission spectra,lower sensitivity and poor stability,making it to be difficult to distinguish the detection signals from self fluorescence of bio-molecules in bio-analytical applications.Quantum dots(QDs)just come to overcome these limitations of organic dyes and attract much attention in analytical and biological chemistry fields.QDs were early prepared mainly through organometallic synthesis.Although the QDs prepared by this kind of methods possess higher photoluminescence quantum efficiency (QYs),it is,however,harsh,complicated to operate and water insoluble.Therefore,QDs preparation directly in aqueous solution has become the research hotspot,eventhough the lower QYs of 10-30%were typically obtained.In this work,L-Glutathione(GSH) stabilized CdTe and CdSe/CdS QDs were directly prepared in aqueous media and used as fluorescent labels in the domain of biological macromolecules probe and immuno-imagings.Firstly,GSH capped highly fluorescent CdTe QDs were prepared by an aqueous approach.Based on interaction of the carboxylic and amino groups on the surface of QDs with the amino and carboxylic groups of antibody,the as prepared CdTe QDs were used as fluorescent labels of biological macro-molecules for cells targeting and imaging.The experimental results showed that CdTe QDs could be conjugated to BSA with the obvious enhancement of photoluminescence intensity and the enhanced fluorescence intensity was proportional to the concentration of BSA in the range 2.0-10 mg/l.Meanwhile the as prepared CdTe QDs were conjugated with CD4 antibody to be the fluorescent labels of mouse T lymphocyte and spleen tissues for immuno imaging.It was demonstrated that CdTe QDs exhibited much better photo stability and stronger fluorescence intensity than FITC,showing a good application potential in the immuno-labeling of cells and tissues.Secondly,the water soluable CdTe QDs were applied as fluorescent markers in prostate cancer research.The as prepared QDs were linked with prostate-specific antigen(PSA) for the direct labeling and linked to immunoglobulin G(IgG) for the indirect labeling of fixed prostate cancer cells.In comparison,the direct labeling procedure was relatively simpler, unfortunately,showing some non-specificity;whereas indirect labeling method eliminated non-specific adsorption by linking of second antibody with QDs,primary antibody with cell or tissues and then the two conjugates,consequently exhibited excellent fluorescence microscopic images.Simultaneously,the prepared QDs were also used to label live prostate cancer cell,to inspect its biological toxicity.Thirdly,GSH capped highly fluorescent CdSe/CdS core-shell quantum dots were firstly prepared by an aqueous approach.Fluorescence emission spectra of as-prepared CdSe/CdS core-shell QDs showed a remarkable enhancement in the emission intensity than that of node CdSe QDs.The TEM results showed that the as prepared CdSe/CdS QDs were approximately spherical in shape with the Size of 5 nm,and monodisperse in aqueous solution.The CdSe/CdS QDs were linked with mouse anti-human CD3 to image human T-lymphocyte.It was demonstrated that the fluorescent CdSe/CdS QDs exhibited much better photo stability and stronger fluorescence intensity than FITC,showing a good application potential in the immuno-labeling of cells.At last,a new kind of materials,the QDs-CNTs nanocomposites were prepared.The nanocomposites are expected to be applied in nano-electrical chemistry,catalytic reaction and biological sensors especially in medical and pharmiceutical science due to its unique physical and chemical properties,and have attracted great attention of the world.In this study,the carboxyl group in the CNTs was linked with the amine group on the QDs after the carbon nanotubes were oxidized,the QDs-CNTs nanocomposites were characterized by fluorescence spectra,showing that after linked with each other,the fluorescence intensity was weakened markedly.In conclusion,two kinds of L-glutathiones stabilized highly fluorescent CdTe and CdSe/CdS quantum dots were prepared by aqueous approach.The as prepared QDs were successfully used as fluorescent labels of biological macro-molecules,such as BSA,CD4 and CD3 antibody,for cells(and tissues) labeling and imaging through the interaction of carboxylic and/or amino groups on the surface of QDs and the amino and/or carboxylic groups on antibody,.The primary experiments about biological toxicity of QDs were also carried out.In addition,the preparation of QDs-CNTs nanocomposites was tried with the preliminary results.