Research On Synthesis & Application Of Quantum Dots And Catalytic Kinetic Spectrophotometric Method Of Rare & Scattered Element Se, Te

The detection of biomacromolecule, such as protein and DNA, need someanalysis method of high sensitivity because of the low content of research object andthe harsh detection condition. The common method is fluorescence analysis,radioactive isotope analysis. Radioactive isotope analysis not only damages thesample but also do harm to the researchers. The disposal of experiment is also aproblem. Because of its high sensitivity, simple and rapid operation, fluorescenceanalysis is widely applied to detect biological samples, such as fluorescence spectrumanalysis and fluorescence microscope imaging analysis. For most biological samples,weak or little fluoscence can be excitated from themselves. So organic fluorochromeis usually adopted to label them and qualitative and quantitative analysis is indirectlycarried out according to the change of fluorescence intensity in the reaction betweenorganic fluorochrome and biological samples. The fatal defect of organicfluorochrome is that photobleaching and photodegradation are easily happen underthe illumination of ultraviolet light and photodecomposition product may damage theorganism. In addition, organic fluorochrome has narrow excitation range and hasserious tailing in its emission peak. So it can not satisfy the need for long time, highsensitivity, multicolor and multicenter biological detection.In the recent years, semiconductor fluorescence nano-patricle—quantum dots(QDs), which possess excellent optical properties, have drawn intense attention as thereplacer of traditional organic fluorochrome in the field of bioluminescence analysisand biological labeling. Quantum dots are semiconductor nano-patricle which consistsofâ…¡-â…¥orâ…¢-â…¤race element. The quantum dots of nanometer scale show specialoptical characteristics: high and stable fluorescence intensity, strong anti- photobleaching ability, broad excitation spectrum,narrow emission spectrum, largerstokes shift, size-tunable, narrow and symmetric emission spectra, emissionwavelength can be controlled by the change of size and composition. Whether thesize-controlled quantum dots are applied as decoding labels in parallel analysis ofmultiple targets, or functionalized quantum dots are applied to in situ imaging andtracing the course of cell metabolism in different fields, in single cell leveldemonstrated its great potential for medical and life sciences applications.Basal studies have revealed that the ion in the analysis can react with the atom onthe surface of quantum dots, certain physical and chemical effects occur, leading tothe surface of quantum dots changes in micro-environment and the fluorescence ofquantum dots changes significantly. Take advantage of this nature, the surface ofquantum dots can be modified to enable it to identify a certain anion or cation withhigh selectivity. Because of the nature, it shows huge advantage in the detection ofmetal ion.Because of its rapid, low-cost, easy integration and automation, etc.,electrochemical biosensor has gradually become a important analysis means in thegenetic testing, anti-cancer drug screening, drug mechanism studies, as well asdiagnosis and treatment of disease areas. It exhibited enormous science andapplication value that excellent spectral characteristics and electrochemical activity ofQuantum dots was caused greatly concern in the novel, high-performanceelectrochemical biosensor.The quantum dots which synthesized by using rare and scattered elements Se andTe have high stability and excellent optical electrochemical properties. Selenium andtellurium play an important part in photosensitive semiconductor devices, computer,communications and aerospace development, energy, medicine and health care, theimportant high-tech equipment areas,they also are the strategic resources which areclosely related to the national economy and people's life. As well as we know, thereserve of rare and scattered elements selenium, tellurium is relatively low (rare) inthe nature, they associates with other metals or minerals and without self-mineralsbasically. So the Analysis methods for selenium and tellurium arise great concern.In this paper, we synthesize the CdSe QDs and CdTe QDs by aqueous approach. The synthesis conditions of the CdTe QDs, which has excellent optical properties andstability, are discussed. New synthesis route of Te precursor has been put forward.Many instruments are used to characterize the optical properties and structure of CdTeQDs. Quantum yield has been calculated. The influence of scattered light on thedetection of fluorescence has been studied and elimination method has been proposedtoo. The changes of fluorescence intensity in the interaction between CdTe QDs ofdifferent sizes are discussed. CdTe QDs is used as fluorescence probe for metal ionsofâ… B,â…¡B race .For their interaction, experimental conditions and selectivity arestudied too. fluorescence resonance energy transfer (FRET)-based DNA probes aredesigned by studying the interaction among CdTe QDs,DNA and daunorubicin(DNR). DNA electrochemical sensor with high-sensitivity and high selectivity isconstructed with CdTe QDs as sensitizer. In addition, the catalytic effect ofselenium, tellurium for the redox reaction between sulfide and methylene blue (MB)are studied. Trace selenium, tellurium are detected by catalytic kinetics method.Major research paper is as follows:The first part mainly studies the synthesis and application on biomacromoleculeand inorganic ions of QDs which composed of rare and scattered element Se, Tecompound.Chapter one mainly contains literature review: First of all, we present theconception, the physical performance, the optical performance and potential toxicityof QDs. Secondly, we present synthetic method of QDs, and the latest researchprogress of traditional organically preparation, aqueous synthesis, surfacemodification and aqueous transform; Thirdly, we present the application of QDs suchas biological marking, cell imaging, fluorescence resonance energy transfer, iondetection, and improving on the application of immunosensor,enzymaticsensor,DNA sensor. Eventually, we present the main research meaning, research contentsand innovation of this article.Chapter two mainly present the synthesis of QDs which composed of Se,Tecompounds. We prepare CdSe QDs and CdTe QDs which taking NaHSe and NaHTeas precursors of Se and Te, and compare the fluorescent spectrum properties andstability of them; the result indicates QDs has more superior spectrum properties and higher stability. We discuss the synthetic condition of QDs, and get the optimumcondition: the molar ratio of Cd²⁺, Te^2-, and MPA,n_Cd2+:n_Te2-is 2:1,n MPA:n_Te2-is5:1,pH is 9.0, the temperature is 96℃.We adopt a new Te precursors prepartionmethod, regard metal Al as reducing agent to prepare(NH₄)₂Te. Comparing with thetraditional method, the stability of (NH₄)₂Te is superior to NaHTe . And(NH₄)₂Te dueto the mild condition of reaction, easy to synthesis in a large amount and store for along time, it is more convenient and reasonable to synthesize.Chapter three mainly signifies the property and the structure of CdTe QDs. Weutilize UV-vis absorb spectrogram, the fluorescent spectrocomparator to signify theoptical performance of different size of QDs, and the size can be controlled byreaction time. With the increasing of the size of QDs, absorption spectrum andfluorescent emission spectrometry become prominently red shift; We use UV-visspectrum absorption edge method, transmission electron microscopy and X-raypowder diffraction to estimate the size of QDs. X-ray powder diffraction has verifiedthat CdTe QDs formated in the laboratory belong to the cubic zincblende structure; IRspectroscopy indicate that CdTe QDs capped with MPA react with CdTe QDs, andachieve the purpose to passivat the surface of CdTe QDs; taking ethanol solution ofrhodamine B as the object of reference, calculate the quantum yield of CdTe QDs is28%; we also study the reason why it produces the scattered light, and the influence todetermine fluorescence, and put forward the method to dispel scattered light; wepropose different size of CdTe QDs interacting with each other may arise"additiveeffects"or"quenching effects", and discuss the reason why it produce.Chapter four mainly study tellurium cadmium quantum dots react with metal ioninâ… B andâ…¡B. Discuss the changes of fluorescent intensity while the emission peak in540nm, 570 nm, 600 nm CdTe QDs react with Cu (â…¡) ,Ag(â… ) ,Hg(â…¡) ,Au(â…¢) ion. Wefind in the experiment, Cu (â…¡) ,Hg(â…¡) ,Au(â…¢) has obvious quenching function to thefluorescent intensity of CdTe QDs .Ag (â… ) quench CdTe QDs at 600 nm while it firstincrease and then quenching fluorescent intensity of CdTe QDs at 540nm,570nm.Under certain condition, system relatively fluorescent intensity(â–³F=F₀-F)arelinear relationship with Cu (â…¡), Ag(â… ), Hg(â…¡), Au(â…¢) ion. The shelter pharmaceuticalEDTA complex function with Cu²⁺orAg⁺, and it will weaken the influence of Cu²⁺/Ag⁺ to the fluorescence intensity of CdTe QDs. Determine simulation sampleAu (â…¢), and its relatively deviation standard is 1.6%. Finally we carried on thediscussion in quenching mechanism.In the fifth chapter, we discuss the interaction between the CdTe QDs -DNAwith daunorubicin (DNR) that based on absorption and fluorescence spectra. Weconclude that DNR can insert the base of the DNA。The DNR and CdTe QDs areindirect adsorption, but have a strong fluorescence quenching that is the form ofenergy transfer quenching。Salt effect and thermal denaturation experiments canfurther prove that the insert functioning between the DNA and the DNR. WeCalculate the Stern-Volmer quenching constant curve Ksv, as well as thethermodynamic parametersâ–³H,â–³G,â–³S, and determine the interact form of binarysystem and the form of fluorescence quenching。In the ternary system, differentmixture order can produced a different fluorescence effects, its causes are described,and on this basis, we design the DNA probe that based on fluorescence resonanceenergy transfer.In the sixth chapter, we described a novel DNA electrochemical biosensor thatwas prepared base on CdTe quantum dots (QDs) and carbon nanotubes (CNTs)modified gold electrode. The ss-DNA probe was covalently attached onto a carboxylcarbon nanotubes modified gold electrode through amines of the DNA bases usingN-hydroxysulfosuccinimide (NHS) and N-(3-dimethylamion) propyl-N'-ethylcarbodiimidehy- drochloride (EDC). After hybridization with the target ssDNA-CdTequantum dots (QDs) nanoconjugates,differential pulse voltammetry(DPV) and cyclicvoltammetry (CV) were used to sensitive detection of the target DNA withdaunomycin (DNR) as the indicator. This DNA electrochemical sensor coulddifferentiate the completely complementary DNA sequence, non-complementaryDNA sequence and Single base mismatch DNA sequence, indicating a goodselectivity. Compared with target DNA sequences without CdTe QDs, CdTe QDslabels on target DNA could obviously improve the sensitivity. Hybridizationconditions determining the sensitivity of the electrochemical assay was investigated.The electrochemical responses suggested that optimal detection of hybridizationoccurred at 55℃for 80 minimums. Under optimal conditions, DNR concentration of 1.67×10^-5 mol/L was chosen as the optimal accumulation concentration. The peakcurrent signal suggested that almost linear with the logarithm of oligodeoxynucleotide(ODN) concentration in the range 1.0×10^-13～1.0×10^-8mol/L with the minimumdetection limit of 3.52×10^-14 mol/L based on the ratio of signal-to-noise of 3, linearregression equation isâ–³I=50.22 +3.5671 1gC_DNA with the correlation coefficient of0.9966. The relative standard deviation (RSD) was 4.8% (n=5) with target DNAsample concentration of 1.0×10^-10 mol/L. It indicated that a satisfactoryreproducibility could be obtained by this DNA electrochemical biosensor.The catalytic kinetic analysis methods of rare and scattered elements-seleniumand tellurium are studied in the second part. The first chapter, preamble includes thefollowing contents: Firstly, we introduce analytical methods development of thesample handling, separation and preconcentration of selenium and tellurium;Secondly, we introduce catalytic kinetic spectrophotometric method in details, thedevelopment of catalytic kinetic spectrophotometric method of selenium and tellurium;finally, we present the main research meaning, research contents and innovation ofthis article.Chapter two studies the method of catalytic kinetic spectrophotometricdetermination of trace selenium. Based on the reaction of methylene blue reductingthioacetamide with selenium (â…£) as catalyses under alkaline conditions, this paperdetermines the trace selenium. Because reaction rate of catalytic reaction has a certainratio relationship with the amount of catalyst in a certain range, the quantitativeanalysis is made according to the relation between the reaction rate and catalyst. Bymeasuring the variation slope (i.e., reaction rate) of difference of the absorbancechanges between the Catalytic reaction and non-catalytic reaction, the quantitativeanalysis of trace selenium in biological samples is realized. The Selenium content inthe range of 0.1～1.0μg/15mL conforms to the Lambert-Beer's law, regressionequation is y=0.0195x-0.0024, correlation coefficient r=0.995, the selenium contentin medlar is measured and the relative standard deviation is 5.4% (n=4), recoveryrate is 90%～96%, calculated the apparent activation energy of catalytic reaction for38.24kJ mol^-1.This method is high sensitivity and reproducibility.Chapter three studies determination of tellurium by catalytic kinetic spectrophotometric. Based on Te (â…£) catalytic reduction S^2- fading reaction ofmethylene blue, a new Kinetic Determination of Trace Tellurium analysis isestablished. By studying the catalytic reaction conditions, the apparent activationenergy of catalytic reaction is determined for 68.94 kJ mol^-1.Te (â…£) concentration isin the range of 20-220 ng mL^-1 Beer's law is obeyed, the linear regression curveequation is y=0.0038 x+0.2191,correlation coefficient r=0.9995, detection limit is3.04 ng mL^-1.The studied separation method of selenium and tellurium is applied fordetermination of trace tellurium of coarse selenium powder. The relative standarddeviation is 3.1% (n =7) and the recovery rate is 98.4%～100.4%.The result of experiment indicate: the research which quantum dots weresynthesized by using rare & scattered elements selenium & tellurium and used influorescence analysis of biomacromolecule and inorganic ions to replace traditionalorganic fluorochrome not only has important science and learned value, but also hasbetter practically application value. The research project is reasonable, the experimentmeans is effectual. It is beneficial to high level research.