Synthesis Of Thick-shell CdSe-Based Core-Shell Structure Quantum Dots And Their Application On Biological Detection

As quasi-zero-dimensional nanomaterials,quantum dots(QDs)have many unique optical properties,such as long photoluminescence decay lifetime,high photoluminescence quantum yield,wide absorption spectra,narrow and tunable band-edge emission,and strong resistance to photobleaching performance.These excellent features make quantum dots have broad application prospects and development potential in the fields of bio-detection,illumination,energy and catalysis.In the 1990 s,researchers first transferred quantum dots from the oil phase to the aqueous phase and prepared them into fluorescent probes for cell imaging.Since then,quantum dots have been extensively studied as fluorescent labeling materials in the fields of single molecule tracing,cell bioimaging,and quantitative detection of specific proteins and nucleic acids.However,when quantum dots are used as fluorescent labeling materials,there is still a problem that high fluorescence quantum yield and high stability cannot be combined,resulting in fluorescence decay of quantum dots during phase transfer and poor fluorescence stability when applied to biological detection.Therefore,it cannot meet the requirements of high sensitivity,high accuracy,long-term effective quantitative rapid detection.Therefore,in order to solve the above problems,this paper attempts to prepare quantum dots with high photoluminescence quantum yield and high stability,and then apply them to detect specific proteins with high-sensitivity.The details are as follows:(1)Synthesis of thick-shell CdSe/CdS/ZnS core-shell quantum dots and their applications in biological detection.The selection of quantum dots shells generally considers two aspects: the first is the range of wavelength required for the experiment.The second is the lattice matching between the core and shells.The lattice mismatch between Cd S and Cd Se is 4%.As a shell material,Cd S is difficult to limit the intranuclear electrons,which will cause the wavelength to red shift.Considering the long photoluminescence decay lifetime and strong penetrating ability of red light,and the impact of biological background can be well avoided in biological detection,so we prefer Cd S as the middle shell.In this experiment,we first synthesized a high-quality Cd Se nucleus with a fluorescence peak at 550 nm by reverse injection method.Then we used 1-Octanethiol as a sulfur source to synthesize a high-quality thick shell by using its slow release at high temperature.The layered Cd Se/Cd S/Zn S core-shell quantum dots have a fluorescence peak of 621 nm,with full-width at half-maximum(FWHM)of 36 nm,and the photoluminescence quantum yield of 75%.After the initial stability test,we used the reverse microemulsion method to silanize the oil-soluble thick-shell quantum dots.It was found that the water-soluble quantum dots after silica-encapsulated have good monodispersity and uniform particle size.The water-soluble silica-encapsulated quantum dots were placed in different complex environments for stability characterization,and the results showed good stability.Finally,based on the water-soluble quantum dots,quantum dots-linked immunosorbent assay was used to quantitatively detect C-reactive protein by screening the ratio of probe diluent and coupled antibody,and the limit of detection(LOD)was 1.11 ng/m L.(2)Synthesis of ultra-thick shell(giant)Cd Se/Zn S/Cd Zn S/Zn S core-shell quantum dots and their application in biological detection.Experiments based on thick shell quantum dots,we found several problems: First,the ability of Cd S-limited electrons is weak,and it is difficult to continuously coat the Cd S shell layer to ensure a high level of photoluminescence quantum yield while continuously increasing the particle size.Second,even thick-shell quantum dots still have large centrifugal losses in the process of water phase preparation because their mass is too small.Third,the photostability of thick-shell quantum dots still needs furture improvement.In view of this,we first selected 2 layers of Zn S to coat the Cd Se core,and then prepared the giant Cd Se/Zn S/Cd Zn S/Zn S core-shell quantum dots through the alloy layer as the intermediate shell.The quantum dots have high photoluminescence quantum yield of 80%,with FWHM of 36 nm,and the relatively uniform particle size.Subsequently,the giant water-soluble quantum dots were subjected to silanization modification and their stability were characterized.The results show that compared with the thick-shell water-soluble quantum dots,the giant water-soluble quantum dots not only show excellent stability,and effectively reduces the centrifugal loss because of its increased own mass.Finally,we optimized the optimal the ratio of antibody coupling and the probe diluent.The high sensitivity detection of C-reactive protein was successfully achieved by quantum dot-linked immunosorbent assay.The LOD was 0.41 ng/m L,and the detection sensitivity was 2.7-fold of thick-shell quantum dots.