Application Of Water Soluble CdTe Quantum Dots In Biological Analysis

As a new type of fluorescent labels,quantum dots (QDs)offer a number of attractivefeatures,including broad excitation spectra,relatively broad and symmetric luminescencebands,large Stokes shift,high photobleaching threshold,good chemical stability and longfluorescence lifetime,which make them have broad protenal application in life science.Even though QDs have been widely used in biomedical,especially in the biologicalfluorescent labeling,but still have a lot of problems to be resolved:How to develop andimprove the QDs synthesis methods,the stability and biocompatibility,as well as how totake better ways to solve QDs coujugated with biological molecules,and how to separateand purify of the conjugates to get stable bioprobes,and so on.At present,most of thebiological applications of QDs come from the organic-phase synthesis,and QDssynthesized in this method have good size distribution and high quantum yield.But thismethod is hard to operate,high cost and toxic.In contrast,water-phase synthesis methodis simple,small toxicity,low cost and good reproducibility,etc.Water-phase synthesis ofQDs can be conjugated directly with biological molecules,which have very broadapplication prospects.The main job of this thesis is to synthesize high-qualitywater-soluble CdTe QDs with different small sulfhydryl molecule as the stabilizer,andalso conduct a study of its optical,surface chemical and bioconjugated properties,andfocused on the specific applications of the as-synthesized QDs as fluorescent labels in thefield of biology and analysis.The main contents and results are summarized as follows:(1)Water-soluble CdTe QDs were synthesized in aqueous solution by using differentsmall sulfhydryl molecules as the stabilizer.The fluorescence emission peaks at 510～660nm are tuned by the control of the refluxing time.The as-synthesized quantum dots werethen characterized by fluorescence spectroscopy,UV-visible spectroscopy,TEM,XRD,EDXS and infrared spectroscopy,respectively.(2)CdTe QDs were synthesized in aqueous solution with 3-Mercaptopropionic acid(MPA)as the stabilizer.Denatured bovine serum albumin (dBSA)has been used tomodify the surface of QDs.Experiment results showed that the dBSA could be effectivelyconjugated to the surface of CdTe QDs.Column chromatography was used to purify the conjugates and determine the optimum conjugate ratio of dBSA to QDs.Furtherexperiment results showed that the dBSA after conjugated to QDs efficiently improve thephotoluminescence quantum yield (PL QY),the chemical stability and the stability againstphotobleaching.A facile and sensitive method for silver (I)ions determination wasproposed based on the fluorescence quenching of the dBSA-QDs.Under the optimumconditions,the relative PL intensity decreased linearly with the silver (I)ions'concentration in the range of 0.08 to 10.66μM.The detection limit was 0.01μM.Thisstudy provides a new trail of thought for the detection of metal cations.(3)The temperature-dependent of CdTe was studied and a method of improving thetemperature-insensitive was established.The PL of CdTe QDs (3.5 nm)is found to betemperature-dependent:as the temperature arising from 278 K to 323 K,the PL intensitydeclines to 50.2% of its original and PL emission peak shows obvious red-shift (～7 nm).After modification of the QDs surface with denatured ovalbumin,the PL is moretemperature-insensitive than before.The PL intensity retains more than 70% of its originaland the emission peak shows less red-shift (～2 nm).Moreover,it is found that the PLintensity and wavelength of denatured ovalbumin coated CdTe QDs are reversible duringheating (323 K)-cooling (278 K)cycles.All the studies provide an important theoreticalbasis for searching temperature-insensitive bioprobes.(4)A new method to detect the ovalbumin was set based on the PL change.Chemically reduced ovalbumin had been used to modify the surface of CdTe QDs,resulting in the enhancement of PL intensity and the blue shift of the PL peak wavelength.A new method for the determination of ovalbumin was established based on the PLchanges.Under the optimal conditions,experiment results showed that the PL intensityand PL peak wavelength were both in good linear with the ovalbumin concentration in therange of 0.125μM～4μM and the detection limit was 0.03μM.The results werecompared with the traditional UV absorption method,and showed relatively goodreliability.(5)Water-soluble core/shell structure with CdTe cores capped by CdS shell(CdTe/CdS)were synthesized in aqueous solution with captosuccinic acid as stabilizer.The absorption and fluorescence spectra confirmed that the synthesized QDs had goodoptical properties.It was observed that the QY of QDs was greatly increased after a heating-cooling cycle (from 22% to 41%).Then the QDs were used to prepare fluorescentprobe.The experiment results showed that the transferrin could conjugate to CdTe/CdSQDs effectively and the HepG2 cells were recognized successfully.This work is of greatsignificance for the preparation of high-powered QDs and their applications in life science.And it has an important reference value for the recognition of cancer cells.(6)High quality of CdTe QDs were synthesized in aqueous solution with glutathioneas the stabilizer.UV-visible spectra and fluorescence spectra confirmed the as-synthesizedQDs had good optical properties.The two-step glutaraldehyde (G)method and one-step Gmethod were compared by the capillary electrophoresis to label con A.Experimentalresults showed that two-step G method has better labeling result.