Photoluminescence of nanocomposites of liquid-crystalline polymers and cadmium selenide quantum dots

The role of specific interactions between a polymer matrix and incorporated quantum dots is one of the critical problems for understanding the effect of the polymer matrix on the optical properties of quantum dots in a nanocomposite material and for creating new photonic materials and related instruments. In this study, cadmium selenide quantum dots have been incorporated into a liquid-crystalline polymer via the interaction of carboxyl groups of the polymer with the quantum-dot surfaces through ionic bonds. From the data of transmission electron microscopy, it has been shown that this interaction provides the localization of quantum dots in the environment of the liquid-crystalline phase of the polymer. Various features of photoluminescent properties have been observed and interpreted in terms of the emission recombination of excitons in CdSe quantum dots, light reabsorption by quantum dots, the effect of the electronic states on the surface CdSe-liquid crystal, and the energy transfer from quantum dots to the polymer liquid-crystalline matrix.     

Preparation and observation of CdS nanometer sized particles incorporated in synthetic opals

Nanometer size particles of CdS were synthesized and incorporated in gem-quality opals by a solution technique. The topological image of sample surface and the site of CdS particles are examined by atomic force microscopy, and the quantum size effect is found in our optical measurements. The possibility of producing arrays of quantum dots and wires is suggested by these observations.     

Theory of alkyl-terminated silicon quantum dots

We have carried out a series of ab initio calculations to investigate changes in the optical properties of Si quantum dots as a function of surface passivation. In particular, we have compared hydrogen-passivated dots with those having alkyl groups at the surface. We find that, while on clusters with reconstructed surfaces complete alkyl passivation is possible, steric repulsion prevents full passivation of Si dots with unreconstructed surfaces. In addition, our calculations show that steric repulsion may have a dominant effect in determining the surface structure and eventually the stability of alkyl-passivated clusters, with results dependent on the length of the carbon chain. Alkyl passivation weakly affects optical gaps of silicon quantum dots, while it substantially decreases ionization potentials and electron affinities and affects their excited state properties. On the basis of our results, we propose that alkyl-terminated quantum dots may be size selected, taking advantage of the change in ionization potential as a function of the cluster size.     

Cu7.2S4量子点玻璃的制备及三阶非线性光学性质

利用溶胶-凝胶法结合气氛控制合成了含Cu7.2S4量子点的玻璃. 通过热重-差热分析仪对干凝胶样品的热分解机制进行了分析, 并利用X射线粉末衍射仪、 X射线光电子能谱、 透射电子显微镜、 X射线能量色散谱)、 高分辨透射电子显微镜及选区电子衍射对 Cu7.2S4量子点在玻璃中的微结构进行了表征, 利用飞秒Z扫描技术研究了材料在800 nm的三阶非线性光学性质. 结果表明, 尺寸在9~21 nm之间的Cu7.2S4纳米晶已经在玻璃中形成, 该玻璃展示出了优异的三阶非线性光学性能, 其三阶非线性光学折射率(γ)、 三阶非线性吸收系数(β)和三阶非线性极化率[X(3)]分别为1.11×10-15 m2/W, 8.91×10-9 m/W和9.56×10-18 m2/V2.     

Preparation,characterization and biocompatibility of aspartic acid modified CdTe quantum dots

This study aims at preparing water soluble aspartic acid （ASP） modified CdTe quantum dots with tunable fluorescence emission controlled by reaction time. The size of the synthesized CdTe quantum dots was evaluated using transmission electron microscope （TEM） and also calculated based on their UV-vis spectra. The optical properties of TGA-CdTe quantum dots were characterized by UV-vis and fluorescence （FL） spectroscopy. The red-shift in the UV-vis absorption and FL emission with the increase of reaction time was observed. The biocompatibility examination indicated that the ASP modified CdTe QDs had low cytotoxicity.     

Novel use of silicon nanocrystals and nanodiamonds in biology

The presented work is aimed at the development of nontoxic nanocrystalline silicon fluorescence labels, biodegradable in living body and long-term stable, and of fluorescent nanodiamonds mainly for in vitro use. These novel fluorescence labels could be very good substitutes for commercially used quantum dots (e.g. cadmium compound quantum dots) which can be toxic according to the latest results. In this work, manufacturing of porous nanocrystalline silicon (por-Si) is described, several basic optical properties of por-Si are presented and the influence of Si nanocrystals, nanodiamonds, and milled silicon on the growth of a cell culture of L929 mouse fibroblast and HeLa cells is compared. Bio-interaction of nanoparticles was studied by optical transmission microscopy, time-lapse microphotography of cell culture evolution, fluorescence microscopy, fluorescence microspectroscopy, and scanning electron microscopy. The size and shape of nanocrystals were determined using atomic force microscopy (AFM).     

High-resolution analytical transmission electron microscopy of semiconductor quantum structures

Analytical transmission electron microscopy was applied to characterize the size, shape, real structure, and, in particular, the composition of different semiconductor quantum structures. Its potential applicability is demonstrated for heterostructures of III-V semiconducting materials and II-VI ones, viz. (In,Ga)As quantum wires on InP and (In,Ga)As quantum dots on GaAs both grown by metal organic chemical vapor deposition, and CdSe quantum dots on ZnSe grown by molecular beam epitaxy. The investigations carried out show that the element distribution even of some atomic layers can be detected by energy-dispersive X-ray spectroscopy, however, exhibiting a smeared profile. Contrary to that, sub-nanometre resolution has been achieved by using energy-filtered transmission electron microscopy to image quantum dot structures.     

核-壳结构CdSe/ZnS量子点的制备、硫醇修饰及其光学性能

采用高温有机相包覆技术制备了CdSe/ZnS核壳结构量子点材料,考察了包覆量对量子点材料的光学性能的影响,研究了含脂肪链和芳香基的双硫醇分子1,4-苯二甲硫醇和1,8-辛二硫醇对于具有核-壳结构的CdSe/ZnS量子点材料的修饰作用,考察了修饰作用对于量子点的量子效率和荧光强度等光学性能的影响.实验结果表明:随着硫化锌包覆量的增加,量子点的量子效率及其荧光发射强度明显提高;硫醇的修饰能显著增强量子点的发光强度,随着硫醇浓度的增加,其发光性能增强,但是达到一定程度后,光学性能基本不随硫醇浓度的变化而变化.根据固体核磁共振等实验结果推测:硫醇分子可能部分替代了量子点体系中的正三辛基氧膦配体,稳定了量子点体系,对量子点起修饰保护作用,从而提高了量子点的光学性能.     

叶酸受体靶向CdS量子点应用于HepG2细胞成像研究

0引言量子点(quantum dots,QDs)又称半导体纳米晶体(semiconductor nanocrystal),是一种由Ⅱ-Ⅵ族或Ⅲ-Ⅴ族元素组成的尺寸在2￣20nm之间,稳定的微     

扫描近场光学显微镜及其在单分子探测中的应用

扫描近场光学显微镜在光学显微镜中具有独特的性能,其突破衍射光限制,具有单分子探测灵敏度,且在研究时不损伤生物样品。文中简要介绍了扫描近场光学显微镜的原理,详述近年来扫描近场光学显微镜在单分子探测中的应用,介绍了扫描近场光学显微镜结合量子点对单分子探测的进展,并对单分子探测的前景做了展望。     

Application of Scanning Tunneling Microscopy and Spectroscopy in the Studies of Colloidal Quantum Qots

Colloidal quantum dots display remarkable optical and electrical characteristics with the potential for extensive applications in contemporary nanotechnology. As an ideal instrument for examining surface topography and local density of states (LDOS) at an atomic scale, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) has become indispensable approaches to gain better understanding of their physical properties. This article presents a comprehensive review of the research advancements in measuring the electronic orbits and corresponding energy levels of colloidal quantum dots in various systems using STM and STS. The first three sections introduce the basic principles of colloidal quantum dots synthesis and the fundamental methodology of STM research on quantum dots. The fourth section explores the latest progress in the application of STM for colloidal quantum dot studies. Finally, a summary and prospective is presented.     

Sensitive and Selective Determination of 2,4,6-Trichlorophenol Using a Molecularly Imprinted Polymer Based on Zinc Oxide Quantum Dots

Novel core-shell molecularly imprinted polymers were prepared based on zinc oxide quantum dots for the determination of 2,4,6-trichlorophenol by fluorescence. Principally, ZnO quantum dots and 2,4,6-trichlorophenol were chosen as the core substrate and the template molecule, respectively. The specific recognition sites for 2,4,6-trichlorophenol were obtained during the polymerization process in presence of 3-aminopropyltriethoxysilane and tetraethylorthosilicate. Molecularly imprinted ZnO quantum dots were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy and the optical properties were evaluated by spectrofluorometry. Under the optimal conditions, molecularly imprinted ZnO quantum dots were successfully applied to the sensitive determination and selective recognition of 2,4,6-trichlorophenol in water. A linear relationship was obtained to cover the concentration range of 0–160?µmol?L^?1 with a correlation coefficient of 0.9931 calculated by the Stern–Volmer equation. The products were used for the determination of 2,4,6-trichlorophenol in the water from local rural areas and the results strongly supported that the molecularly imprinted ZnO quantum dots were suitable for the determination of 2,4,6-trichlorophenol in real examples.     

Influence of cobalt concentration on structural and optical properties of ZnS quantum dots

ZnS and Co-doped ZnS nanoparticles have been prepared by simple chemical precipitation method. Zinc acetate, sodium sulfide, and cobalt nitrate have been used as precursors for the preparation of Co-doped ZnS quantum dots. The X-ray diffraction results revealed that the undoped and Co-doped ZnS quantum dots exhibit hexagonal structure. The average grain size of quantum dot was found to lie in the range of 2.6–3.8 nm. The surface morphology has been studied using scanning electron microscope. The compositional analysis results confirm the presence of Co, Zn and S in the sample. The optical properties of undoped and Co-doped ZnS quantum dots have been studied using absorption spectra. TEM results show that undoped and Co-doped ZnS nanoparticles exhibit a uniform size distribution with average size of 2.5–3.4 nm.     

Quantum dot micropatterning on si

Using InP and PbSe quantum dots, we demonstrate that the Langmuir-Blodgett technique is well-suited to coat nonflat surfaces with quantum dot monolayers. This allows deposition on silicon substrates covered by a developed patterned resist, which results in monolayer patterns with micrometer resolution. Atomic force microscopy and scanning electron microscopy reveal the formation of a densely packed monolayer that replicates predefined structures with high selectivity after photoresist removal. A large variety of shapes can be reproduced and, due to the excellent adhesion of the quantum dots to the substrate, the hybrid approach can be repeated on the same substrate. This final possibility leads to complex, large-area quantum dot monolayer structures with micrometer spatial resolution that may combine different types of quantum dots.     

Synthesis and characterization of mondispersed CdSe nanocrystals at lower temperature

Nearly monodispersed CdSe quantum dots have been prepared by a soft solution approach using air-stable reagents at lower temperature. The temporal evolution of the absorption and room temperature photoluminescence spectra were used to follow the reaction process and to characterize the optical properties of as-prepared CdSe quantum dots. The results exhibited clear exciton peaks in absorption and bright band-edge luminescence. The structures of the CdSe nanocrystals were determined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The influence of the temperature on the properties of the resultant CdSe nanocrystals was investigated. The distribution of properties within ensembles of CdSe nanocrystals was also studied. A drastic difference in the photoluminescence efficiencies of size-selected fractions was observed.     

Organometal halide perovskite quantum dots: synthesis,optical properties,and display applications

In recent two years, organometal halide perovskites quantum dots are emerging as a new member of the nanocrystals family. From the chemical point of view, these perovskites quantum dots can be synthesized either by classical hot-injection technique for inorganic semiconductor quantum dots or the reprecipitation synthesis at room temperature for organic nanocrystals. From a physical point of view, the observed large exciton binding energy, well self-passivated surface, as well as the enhanced nonlinear properties have been of great interest for fundamental study. From the application point of view, these perovskites quantum dots exhibit high photoluminescence quantum yields, wide wavelength tunability and ultra-narrow band emissions, the combination of these superior optical properties and low cost fabrication makes them to be suitable candidates for display technology. In this short review, we introduce the synthesis, optical properties, the prototype light-emitting devices, and the current important research tasks of halide perovsktie quantum dots, with an emphasis on CH₃NH₃PbX₃ (X=Cl, Br, I) quantum dots that developed in our group.     

Water-soluble silica-overcoated CdS:Mn/ZnS semiconductor quantum dots

Highly luminescent and photostable CdS:Mn/ZnS core/shell quantum dots are not water soluble because of their hydrophobicity. To create water-soluble quantum dots by an appropriate surface functionalization, CdS:Mn/ZnS quantum dots synthesized in a water-in-oil (W/O) microemulsion system (reverse micelles) were consecutively overcoated with a very thin silica layer ( approximately 2.5 nm thick) within the same reverse micellar system. The water droplet serves as a nanosized reactor for the controlled hydrolysis and condensation of a silica precursor, tetraethyl orthosilicate (TEOS), using an ammonium hydroxide (NH4OH) catalyst. Structural characterizations with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) indicate that the silica-quantum dot nanocomposites consist of a layered structure. Owing to the amorphous, porous nature of a silica layer, the optical and photophysical properties of silica-overcoated CdS:Mn/ZnS quantum dots are found to remain close to those of uncoated counterparts.     

单分子定位超分辨显微成像有机荧光探针的研究进展

在生物医学领域,对纳米尺寸级别的微小生物目标进行精确定位研究具有非常重要的意义,而光学显微成像技术为此提供了强有力的工具。 光学显微成像技术受到光学衍射极限的限制,难以分辨尺寸在衍射极限(<200 nm)以下的生物结构,无法直接获取微小生物结构信息,阻碍了生物医学的进一步发展。 近年来,随着纳米分辨显微成像技术的出现,新型荧光探针的开发、成像系统与设备的不断发展及成像算法不断完善地深入结合,促进了光学衍射极限以下尺寸微观目标的研究。 基于单分子定位的超分辨荧光显微成像(SMLM)包括光激活定位成像(PALM)与随机光学重构超分辨成像(STORM),将有机荧光探针与超分辨光学显微成像技术紧密结合在一起,荧光探针的光物理性质直接决定着超分辨成像结果的好坏。 因此,设计不同性能的荧光探针可以实现超精细结构的不同超分辨成像,为研究其生物学功能提供了有力的工具。 本文着重围绕基于SMLM的原理、有机荧光探针的设计要求、用于SMLM的荧光探针种类及其生物应用等方面进行总结综述,指出了单分子定位成像上存在的不足,并对其发展方向进行了展望,希望为对超分辨成像研究感兴趣或初涉该领域的研究者提供成像理论与探针设计方面的帮助。     

Fluorescent II-VI semiconductor quantum dots in living cells: nonlinear microspectroscopy in an optical tweezers system

In this work we used a setup consisting of an optical tweezers combined with a nonlinear microspectroscopy system to perform scanning microscopy and obtain emission spectra using two photon excited (TPE) luminescence of captured single living cells labeled with core-shell fluorescent semiconductor quantum dots (QDs). The QDs were obtained via colloidal synthesis in aqueous medium with an adequate physiological resulting pH. Sodium polyphosphate was used as the stabilizing agent. The results obtained show the potential presented by this system as well as by these II-VI fluorescent semiconductor quantum dots to perform spectroscopy in living trapped cells in any neighborhood and dynamically observe the cell chemical reactions in real time.     

Cellular uptake and subcellular localization of highly luminescent silica-coated CdSe quantum dots--in vitro and in vivo

With excellent optical properties, quantum dots (QDs) have been made as attractive molecular probes for labeling cells in biological research. The purpose of the present work is to explore the possible role of silica-coated cadmium selenide (CdSe) QDs in the in vitro and in vivo cellular uptake and their subcellular localization. The in vitro uptake characteristics of silica-coated CdSe QDs were performed in cultured New Zealand rabbit adipose tissue-derived mesenchymal stem cells (RADMSCs) and Human cervical cancer cells (HeLa) using fluorescence microscopy after staining with 4,6-diamidino-2-phenylindole (DAPI). The in vitro results showed that the silica-coated CdSe QDs were efficiently taken up by the cells and it was localized in the intracellular vesicles giving strong fluorescence from the cytoplasm and nearby nucleus. Subsequently, the in vivo localization and distribution of QDs were studied by the hematoxilin stained semithin cryosections of tissues (~15 μm thickness) under fluorescence microscopy and ultrathin sections of tissues (~100 nm thickness) under confocal laser scanning microscopy at the distribution maxima. Our in vivo results confirmed the effective cellular uptake and even distribution pattern of QDs in tissues. Overall, these in vitro and in vivo results are represented with focus on internalization, subcellular localization and distribution of the QDs, in view of their potential applications in biomedical field.