水溶性的CdSe/CdS/ZnS量子点的合成及表征

用L-半胱氨酸盐(Cys)作为稳定剂,合成了水溶性的双壳结构的CdSe/CdS/ZnS半导体量子点。吸收光谱和荧光光谱结果表明,双壳结构的CdSe/CdS/ZnS纳米微粒比单一的CdSe核纳米粒子和单核壳结构的CdSe/CdS纳米粒子具有更优异的发光特性。用透射电子显微镜(TEM)、ED、XRD、XPS和FTIR等方法对CdSe核和双壳层的CdSe/CdS/ZnS纳米微粒的结构、分散性及形貌分别进行了表征。     

CdSe/CdS/SiO2复合纳米球的制备及发光性能

采用两相法合成了CdSe/CdS核-壳结构的量子点, 用氨水催化水解正硅酸乙酯制得复合结构的CdSe/CdS/SiO₂发光纳米球. 通过对量子点用量、氨水用量、反应时间及溶剂比例等实验条件的调节, 得到了单分散性较好, 尺寸在23~145 nm的复合发光纳米球. 利用紫外-可见吸收光谱和荧光发射光谱对其发光性能进行了研究, 同时利用透射电镜(TEM)观察复合纳米球的形貌. 结果表明, 复合发光纳米球样品的最高荧光量子产率可达8%.     

水溶性CdSe/CdS量子点的合成及其与牛血清蛋白的共轭作用

用巯基乙酸(TGA)作为稳定剂，合成了水溶性的CdSe和核壳结构的CdSe/CdS半导体量子点。吸收光谱和荧光光谱研究表明，核壳结构的CdSe/CdS半导体量子点比单一的CdSe量子点具有更优异的发光特性。用TEM、电子衍射(ED)和XPS分别表征了CdSe和CdSe/CdS纳米微粒的结构、形貌及分散性。红外光谱和核磁共振谱证实了巯基乙酸分子中的硫原子和氧原子与纳米微粒表面的金属离子发生了配位作用。在pH值为7.4的条件下，将合成的CdSe和CdSe/CdS量子点直接与牛血清白蛋白(BSA)相互作用。实验发现，两种量子点均对BSA的荧光产生较强的静态猝灭作用；而BSA对两种量子点的荧光则具有显著的荧光增敏作用，存在BSA时CdSe/CdS量子点的荧光增强是不存在BSA时体系荧光强度的3倍。     

柠檬酸稳定的水溶性CdSe和CdSe/CdS量子点的荧光特性

用柠檬酸(citrate)作为稳定剂合成了尺寸分布集中、荧光性质良好的水溶性CdSe量子点。通过调节合成温度可以调控CdSe量子点的尺寸及相应的最大荧光发射波长。当温度由20 ℃增加到95 ℃时,合成的CdSe量子点的平均尺寸由2.0 nm增加到3.2 nm,相应的荧光发射峰由500 nm红移到570 nm,展现出明显的量子尺寸效应。进一步制备了CdSe/CdS核壳量子点,其荧光量子产率比CdSe增加了5～10倍。系统地研究了S/Se物质的量的比对CdSe/CdS量子点荧光特性的影响,通过XPS证实了CdSe/CdS量子点中CdS壳层的存在。利用红外光谱和核磁共振波谱表征了柠檬酸分子中的羧基和羟基氧原子与CdSe量子点表面的Cd离子的配位作用,进而揭示了柠檬酸分子对水溶性CdSe量子点溶液的稳定作用。     

水溶性CdSe/CdS纳米晶合成条件的优化研究

以巯基乙醇为修饰剂,在水溶液中合成了稳定的CdSe/CdS纳米晶,应用单因素法和多目标单纯形法探索合成条件。通过透射电镜观察所合成的纳米晶的形貌和大小,用紫外-可见吸收光谱和荧光光谱对其光学特性进行了表征。并且以L-色氨酸荧光量子产率0.14为标准,测量了合成的CdSe/CdS纳米晶的荧光量子产率为0.37。     

CdS和CdSe新型纳米结构的高效溶剂热合成

采用快速高效的溶剂热法合成了海星形CdS纳米结构和一维CdSe纳米结构。用XRD、SEM和UV-Vis等表征手段对产物进行了表征，结果表明产物为单一的CdS和CdSe纳米结构，且CdS纳米结构具有良好的分散性，其形成极大地受到pH值影响，而CdSe先形成层状的二维结构、再形成一维纳米结构。     

介观结构SiO2/CdO纳米复合物为前驱体原位水热合成半导体CdSe和CdS纳米晶

以高度有序的介观结构SiO₂/CdO纳米复合物为前驱体,在硒源或硫源存在的还原性条件下,利用原位水热反应,合成了介观结构SiO₂/CdSe及SiO₂/CdS纳米复合物,除去SiO₂后,得到半导体CdSe及CdS纳米晶.通过X射线衍射(XRD),高分辨率透射电镜(HRTEM),X射线能散射谱(EDX)及选区电子衍射(SAED)等手段对产物进行了组成和结构表征.结果表明,介观结构SiO₂主体材料在合成过程中起到了一定的形貌和尺寸限制作用,得到的CdSe和CdS均为直径在8 nm左右的类球形六方相纳米晶.     

双官能Fe3O4/CdSe/CdS荧光磁性复合物的制备和表征

采用化学共沉淀法, 以FeCl₂•4H₂O和FeC1₃•6H₂O为原料制备磁性Fe₃O₄纳米颗粒(MNPs), 采用氨基酸对其进行修饰使其表面连上氨基. 用巯基乙酸作为稳定剂合成了水溶性的CdSe/CdS量子点, 并利用偶联剂1-乙基-3-(3-二氨丙基)碳二亚胺盐酸盐(EDC)和N-羟基琥珀酰亚胺(NHS)连接氨基修饰的Fe₃O₄和带有羧基的CdSe/CdS, 成功制备了Fe₃O₄/CdSe/CdS荧光磁性纳米颗粒. 该荧光磁性纳米复合物保留了CdSe/CdS量子点优异的荧光特性, 平均粒径在40 nm左右; 磁化曲线表明此纳米复合物具有超顺磁性. 这种双官能复合纳米颗粒有望成为新型荧光磁性双标记复合微粒而广泛应用于免疫检测、荧光追踪、磁性分离等领域.     

CdS量子点与CdSe量子点间荧光共振能量转移研究

在有机相中合成了不同尺寸的CdS和CdSe量子点, 并利用Langmuir-Blodgett (LB)技术将相同尺寸的CdS和CdSe量子点组装成多层复合纳米有序结构. 采用荧光光谱研究了CdS和CdSe量子点在混合体系和多层复合纳米有序结构状态下的荧光共振能量转移(Fluorescence resonance energy transfer, FRET). 我们观察到CdS和CdSe量子点混合溶液与当溶剂挥发形成固态膜中, CdS量子点的荧光强度较溶液状态下强烈猝灭, 表明当颗粒间距离减小时CdS和CdSe量子点间产生较高效率的荧光共振能量转移. 在多层复合纳米有序结构中, 随着给体CdS量子点层数的增加, 单层受体CdSe量子点的荧光逐步增强, 这表明层间纵向能量转移率随给体层数的增加而提高.     

水溶性的CdSe/ZnS纳米微粒的合成及表征

用L-半胱氨酸(Cys)作为稳定剂，合成了水溶性的CdSe/ZnS核壳结构的半导体纳米微粒。吸收光谱和荧光光谱表明，CdSe/ZnS纳米微粒比单一的CdSe纳米粒子具有更优异的发光特性。透射电子显微镜（TEM）、ED和XPS表征了CdSe/ZnS纳米微粒的结构、分散性及形貌。红外光谱证实半胱氨酸分子中的硫原子和氧原子参加了与纳米粒子表面的金属离子的配位作用。     

Preparation and application of L-cysteine-modified CdSe/CdS core/shell nanocrystals as a novel fluorescence probe for detection of nucleic acid

The water-soluble L-cysteine-modified CdSe/CdS core/shell nanocrystals (expressed as CdSe/CdS/Cys nanocrystals) have been synthesized in aqueous by using L-cysteine as stabilizer. The size, shape, component and spectral property of CdSe/CdS/Cys nanocrystals were characterized by high-resolution transmission electron microscope (HRTEM), energy dispersive X-ray fluorescence (EDX), infrared spectrum (IR) and photoluminescence (PL). The results showed that the spherical CdSe/CdS/Cys nanocrystals with an average diameter of 2.3 nm have favorable fluorescent property, theirs photostability and fluorescence intensity are enhanced greatly after overcoating with CdS. The cysteine modified on the surface of core/shell CdSe/CdS nanocrystals renders the nanocrystals water-soluble and biocompatible. Based on the fluorescence quenching of the nanocrystals in the presence of calf thymus deoxyribonucleic acid (ct-DNA), a fluorescence quenching method has been developed for the determination of ct-DNA by using the nanocrystals as a novel fluorescence probe. The pH value of the system was selected at pH 7.4, with excitation and emission wavelength at 380 and 522 nm, respectively. Under the optimal conditions, the fluorescence quenching intensity of the system is linear with the concentration of ct-DNA in the range of 0.1-3.5 microg/mL (r=0.9987). The detection limit is 0.06 microg/mL. And two synthetic samples were analyzed satisfactorily.     

Ultrafast Carrier Dynamics in CdSe/CdS/ZnS Quantum Dots

The intra- and inter-band relaxation dynamics of CdSe/CdS/ZnS core/shell/shell quantum dots are investigated with the aid of time-resolved nonlinear transmission spectra which are obtained using femtosecond pump-probe technique. By selectively exciting the core and shell carrier, the dynamics are studied in detail. Carrier relaxation is found faster in the conduction band of the CdS shell (about 130 fs) than that in the conduction band of the CdSe core (about 400 fs). From the experiments it is distinctly demonstrated the existence of the defect states in the interface between the CdSe core and the CdS shell, indicating thatultrafast spectroscopy might be a suitable tool in studying interface and surface morphology properties in nanosystems.     

Highly Stable CdSe/CdS/ZnS Fluorophores in Acidic Environment: Acile Preparation and Modification of Core/shell/shell Nanocrystals

We described a facile method for preparing CdSe/CdS/ZnS core/shell/shell nanocrystals from air-stable single source precursors.The single source precursors of cadmium ethylxanthate and zinc ethylxanthate were used to form CdS and ZnS shell layers in octadecene.An efficient modification of CdSe/CdS/ZnS nanocrystals was subsequently performed to obtain hydrophilic nanocrystal fluorophores with good stability in a pH range of 1.6-10.     

Probing cytotoxicity of CdSe and CdSe/CdS quantum dots

Toxicities of CdSe and CdSe/CdS quantum dots(QDs) synthesized by ultrasound-assisted methods were investigated in vitro and in vivo.Five human cell lines were used to assess the cytotoxicity of as-prepared CdSe and CdSe/CdS by assays of MTT viability,red blood cell hemolysis,flow cytometry,and fluorescence imaging.The results show that these QDs may be cytotoxic by their influence in S and G2 phases in cell cycles.The cytotoxicity of QDs depends on both the physicochemical properties and related to target cells.     

Synthesis and Characterization of CdSe Nanocrystals Capped by CdS

CdSe semiconductor nanocrystals capped by CdS were synthesized in the aqueous solution with 2-mercaptoethanol as the stabilizer. The CdS capping with a higher band-gap than that of the core crystallite has successfully eliminated the surface traps. Optical absorption and fluorescence emission spectra were used to probe the effect of CdS passivation on the electronic structure of the nanocrystals. The composite CdSe/CdS nanocrystals exhibit strong, narrow(FWHM≤40 nm) and stable band-edge photoluminescence. X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy were used to analyze the composite nanocrystals and determine their average size, size distribution, shape, internal structure and elemental composition.     

Photoassisted synthesis of CdSe and core-shell CdSe/CdS quantum dots

This paper describes the synthesis of core-shell CdSe/CdS quantum dots (QDs) in aqueous solution by a simple photoassisted method. CdSe was prepared from cadmium nitrate and 1,1-dimethylselenourea precursors under illumination for up to 3 h using a pulsed Nd:YAG laser at 532 nm. The effects that the temperature and the laser irradiation process have on the synthesis of CdSe were monitored by a series of experiments using the precursors at a Cd:Se concentration ratio of 4. Upon increasing the temperature (80-140 degrees C), the size of the CdSe QDs increases and the time required for reaching a maximum photoluminescence (PL) is shortened. Although the as-prepared CdSe QDs possess greater quantum yields (up to 0.072%) compared to those obtained by microwave heating (0.016%), they still fluoresce only weakly. After passivation of CdSe (prepared at 80 degrees C) by CdS using thioacetamide as the S source (Se:S concentration ratio of 1) at 80 degrees C for 24 h, the quantum yield of the core-shell CdSe/CdS QDs at 603 nm is 2.4%. Under UV irradiation of CdSe/CdS for 24 h using a 100-W Hg-Xe lamp, the maximum quantum yield of the stable QDs is 60% at 589 nm. A small bandwidth (W1/2 < 35 nm) indicates the narrow size distribution of the as-prepared core-shell CdSe/CdS QDs. This simple photoassisted method also allows the preparation of differently sized (3.7-6.3-nm diameters) core-shell CdSe/CdS QDs that emit in a wide range (from green to red) when excited at 480 nm.     

Single-source precursor route for overcoating CdS and ZnS shells around CdSe core nanocrystals

We reported a facile route for overcoating CdS and ZnS shells around colloidal CdSe core nanocrystals. To synthesize such double shelled core/shell nanocrystals, first, CdSe core nanocrystals were prepared in a much “greener” and cheap route, which did not involve the use of hazardous and expensive trioctylphosphine. Then, a low-cost and labor-saving route was adopted for the CdS and ZnS shell growth with the use of thermal decomposition of commercial available air stable single-source precursors cadmium diethyldithio-carbamate and zinc diethyldithiocarbamate in a non-coordinating solvent at intermediate temperatures. Powder X-ray diffraction patterns and transmission electron microscopy images confirm the epitaxial growth of the shell in the core/shell nanocrystals. The photoluminescence quantum yield of the resulting CdSe/CdS/ZnS core/shell nanocrystals can be as high as 90% in organic media and up to 60% after phase transfer into aqueous media. By varying the size of CdSe cores, the emission wavelength of the obtained core/shell nanostructures can span from 554 to 636 nm.