Preparation and characterization of monodisperse CdS quantum dot‐polymer microspheres

A novel and effective method for the preparation of monodisperse CdS quantum dot‐polymer microspheres was proposed. The monodisperse hollow polymer microspheres were firstly swelled in chloroform. Then, the reaction precursor composed of CdO and sulfur, was impregnated into the hollow polymer microspheres. Subsequently, the CdS quantum dots were synthesized directly within the polymer microspheres by thermal decomposition. The morphology, structure, and fluorescence properties of CdS quantum dot‐polymer microspheres were studied by scanning electron microscope, transmission electron microscope, fluorescence microscope, and flow cytometry. The results indicate that the fluorescent CdS quantum dots are successfully synthesized in the monodisperse hollow polymer microspeheres, which provide very strong fluorescence intensity, and offer excellent photostability due to the compact structure of the polymer matrix. These CdS quantum dot‐polymer microspheres have potential applications in biotechnology and biomedicine. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 751–755, 2010     

Synthesis and characterization of micron‐sized monodisperse superparamagnetic polymer particles with amino groups

Micron‐sized monodisperse superparamagnetic polyglycidyl methacrylate (PGMA) particles with functional amino groups were prepared by a process involving: (1) preparation of parent monodisperse PGMA particles by the dispersion polymerization method, (2) chemical modification of the PGMA particles with ethylenediamine (EDA) to yield amino groups, and (3) impregnation of iron ions (Fe²⁺ and Fe³⁺) inside the particles and subsequently precipitating them with ammonium hydroxide to form magnetite (Fe₃O₄) nanoparticles within the polymer particles. The resultant magnetic PGMA particles with amino groups were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X‐ray diffractometry (XRD), and vibrating sample magnetometry (VSM). SEM showed that the magnetic particles had an average size of 2.6 μm and were highly monodisperse. TEM demonstrated that the magnetite nanoparticles distributed evenly within the polymer particles. The existence of amino groups in the magnetic polymer particles was confirmed by FTIR. XRD indicated that the magnetic nanoparticles within the polymer were pure Fe₃O₄ with a spinel structure. VSM results showed that the magnetic polymer particles were superparamagnetic, and saturation magnetization was found to be 16.3 emu/g. The Fe₃O₄ content of the magnetic particles was 24.3% based on total weight. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3433–3439, 2005     

Facile synthesis of fluorescent quantum dot‐polymer nanocomposites via frontal polymerization

We report an available approach for quickly fabricating CdS QD‐polymer nanocomposites via frontal polymerization (FP). First, we synthesized (3‐mercaptopropyl)‐1‐trimethoxysilane (MPS)‐capped CdS quantum dots (QDs). With these MPS‐capped CdS QDs containing mercapto groups, MPS‐capped CdS QDs can be easily incorporated into a poly(N‐methylolacrylamide) (PNMA) matrix via FP. A variety of features for preparing QD‐polymer nanocomposites, such as initiator concentration and CdS concentration, were thoroughly investigated. The fluorescence properties of QD‐polymer nanocomposites prepared via FP are comparatively investigated on the basis of ultraviolet–visible (UV–vis) spectra and photoluminescence (PL) spectra. Results show that the PL intensity of QD‐polymer nanocomposites prepared via the FP method is superior to that obtained by the traditional batch polymerization (BP) method. In addition, by measuring the changes of PL intensity of the samples immersed in different concentrations of copper acetate solution, we found the QD‐polymer nanocomposites can be ultrasensitive to copper ions. This FP process can be exploited as a facile and rapid way for synthesis QD‐polymer nanocomposites on a large scale, avoiding the fluorescence quenching of nanocrystals during incorporation nanocrystals into polymer matrices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2170–2177, 2010     

Synthesis of ZnO nanorods and their application in quantum dot sensitized solar cells

ZnO nanorod thin films of different thicknesses and CdS quantum dots have been prepared by chemical method. X-ray diffraction pattern reveals that the CdS quantum dot and ZnO nanorods are of hexagonal structure. Field emission scanning electron microscope images show that the diameter of hexagonal shaped ZnO nanorods ranges from 110 to 200 nm and the length of the nanorod vary from 1.3 to 4.7 μm. CdS quantum dots with average size of 4 nm have been deposited onto ZnO nanorod surface using successive ionic layer adsorption and reaction method and the assembly of CdS quantum dot with ZnO nanorod has been used as photo-electrode in quantum dot sensitized solar cells. The efficiency of the fabricated CdS quantum dot-sensitized ZnO nanorod-based solar cell is 1.10 % and is the best efficiency reported so far for this type of solar cells.     

Organized quantum dot array through nanochemistry

Well defined tetrahedral cadmium sulfide nanocrystals were made in a rational way by organometallic chemical synthesis. Due to the fair degree of the ionic character in Cd—S bond, the sulfide S^2– can be replaced by the organothiolate RS^– without disrupting the CdS lattice structure. These ligands were delicately chosen to fabricate anisotropically capped nanocrystals. During solvent evaporation, these smart dots have the property to self-connect in a head-to-tail alignment leading to a new fibrous polymeric dot material. These quantum microcrystallites can be processed to make powder, free standing dots or optically transparent and anisotropic films. Optical spectroscopy, X-ray diffraction and electron microscopy have been used to characterize this organized quantum dot array.     

荧光磁性双功能树状分子微球的制备与表征

采用化学共沉淀法, 以FeCl₃·6H₂O和FeSO₄·7H₂O为原料制备了磁性Fe₃O₄纳米颗粒, 采用树状大分子对其进行修饰, 然后通过树状大分子具有的大量空腔及末端丰富的氨基, 经吸附、 键合, 与大量巯基乙酸修饰的CdSe/CdS量子点连接, 得到三代具有荧光磁性双功能的树状分子微球, 并对其进行结构表征与性能测试. 结果表明: 三代复合后的微球的平均粒径分别为15, 34和49 nm; 一代荧光磁性微球的发光性能最佳, 其量子产率达24.1%; 零代荧光磁性微球磁性能最优, 其饱和磁化强度为15.96 A·m²/kg. 这种具有荧光和磁性的双功能纳米复合微粒有望在免疫检测、 靶向治疗、 荧光追踪和磁性分离等方面得到广泛应用.     

The electrochemical behavior of core-shell CdSe/CdS magic-sized quantum dots linked to cyclodextrin for studies of the encapsulation of bioactive compounds

Semiconductor nanocrystal quantum dots have been the subject of extensive investigations in different areas of science and technology in the past years. In particular, there are few studies of magic-sized quantum dots (MSQDs), even though they exhibit features such as extremely small size, fluorescence quantum efficiency, molar absorptivity greater than traditional QDs, and highly stable luminescence in HeLa cell cultures, thereby enabling monitoring of biological or chemical processes. The present study investigated the electrochemical behavior of free CdSe/CdS MSQDs using glassy carbon electrode and CdSe/CdS MSQDs immobilized on a gold electrode modified with a self-assembled cyclodextrin monolayer. The MSQDs showed two peaks in aprotic medium. The functionalized film modifier was prepared and characterized by means of cyclic voltammetry and electrochemical impedance spectroscopy using ferricyanide ions as a redox probe. The prepared modified electrode exhibited a stable behavior. The proposed method was successfully applied to encapsulation studies of mangiferin, a natural antioxidant compound, and cyclodextrin associated with the quantum dot, and the response was compared with that of the modified electrode without QD. The fluorescence study revealed that CdSe/CdS quantum dots emit blue light when excited by an optical source of wavelength of 350 nm and a significant increase in fluorescence and absorbance intensity is observed from the core-shell CdSe/CdS MSQDs when quantities of mangiferin are added to the solution containing thiolated cyclodextrin. CdSe/CdS MSQDs are optically and electrochemically sensitive and can be used for the detection and interaction of compounds encapsulated in cyclodextrin.     

Porous phosphate heterostructures containing CdS quantum dots: assembly, characterization and photoluminescence

The synthesis and characterization of cadmium sulphide (CdS) quantum dots, conjugated in a porous phosphate heterostructure functionalized with aminopropyl groups is described. The resulting material has fluorescence properties with maximum emission intensity at 575 nm. The fluorescent materials are not soluble in water and exhibit high stability in aqueous solution in the pH ranges from 2 to 9. Energy dispersive X-ray spectroscopy confirmed the qualitative elemental composition of the synthesized materials and X-ray photoelectron spectra showed a surface S/Cd atomic ratio of 1.09. SEM images show that the materials are amorphous, possessing porous with sizes of several tens nanometres, homogeneous and exhibit a layered morphology. The adsorption–desorption analysis by N₂ at 77 K showed the accessibility of the CdS quantum dots onto the pores of the structure. The CdS quantum dots were stabilized by mercaptopropionic acid and bounded to the host materials by amine groups.     

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.     

镉(Ⅱ)-半胱氨酸配合物对CdS量子点的荧光增强作用及其在离子检测中的应用

合成了弱配体柠檬酸三钠修饰的CdS量子点(Cit-CdS QDs), 透射电子显微镜表征结果表明, Cit-CdS QDs的粒径分布均匀(4~6 nm), 分散性好。 研究了金属离子(银(Ⅰ)离子、镉(Ⅱ)离子)、巯基化合物(巯基乙酸、半胱氨酸)以及金属离子(银(Ⅰ)离子、镉(Ⅱ)离子)与巯基化合物形成的配合物对Cit-CdS QDs荧光的影响。 发现金属离子(银离子、镉离子)与巯基化合物(巯基乙酸、半胱氨酸)形成的水溶性配合物可以显著增强Cit-CdS QDs的荧光, 配合物对Cit-CdS QDs的增强程度比单独的金属离子或巯基化合物均要高, 而且配合物修饰的CdS QDs对铜(Ⅱ)离子的响应要高于单独用金属离子或巯基化合物修饰的量子点。 建立了铜(Ⅱ)离子高灵敏度荧光检测方法, 该方法检测范围宽(1.0×10^-8~1.0×10^-6 mol/L), 检测限低(1.0×10^-9 mol/L)且具有很好的选择性, 拓展了配合物作为量子点修饰剂的应用。     

In-situ encapsulation of quantum dots into polymer microspheres

We have incorporated fluorescent quantum dots (QDs) into polystyrene microspheres using functionalized oligomeric phosphine (OP) ligands. We find that a uniform distribution of quantum dots is loaded inside each polymer bead. Some local close-packing of quantum dots in the beads is attributed to the self-polymerization of the functionalized ligands. The presence of quantum dots disturbs the nucleation and growth processes during the formation of polymer microspheres and results in a wider size distribution of the quantum dot-embedded polystyrene beads than for the control without dots. The change in quantum efficiency of the quantum dots before (approximately 20%) and after (12%) loading into the beads substantiates the protection of oligomeric phosphine ligands yet indicates that the properties of these quantum dots are still affected during processing.     

Synthesis and curing of poly(glycidyl methacrylate) nanoparticles

Glycidyl‐functional polymer nanoparticles [poly(glycidyl methacrylate) (PGMA)] were fabricated with microemulsion polymerization. The successful fabrication of PGMA nanoparticles was confirmed by Fourier transform infrared spectroscopy and transmission electron microscopy (TEM). A TEM image showed that the average diameter of the PGMA nanoparticles was approximately 10–28 nm and was fairly monodisperse. As the surfactant concentration increased, the average size of the nanoparticles decreased and approached an asymptotic value. A significant reduction of the nanoparticle size to the nanometer scale led to an enhanced number of surface functionalities, which played an important role in the curing reaction. The PGMA nanoparticles were cured with a low‐temperature curing agent, diethylene triamine, to produce ultrafine thermoset nanoparticles. The low‐temperature curing process was performed below the glass‐transition temperature of PGMA to prevent the coagulation and deformation of the nanoparticles. A TEM image indicated that the cured PGMA nanoparticles did not exhibit interparticle aggregation and morphological transformation during curing. The average size of the cured PGMA nanoparticles was consistent with that of the pristine PGMA nanoparticles © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2258–2265, 2005     

Light conversion efficiency of flower like structure TiO<Subscript>2</Subscript> thin film solar cells

Flower like structure TiO₂ thin films have been grown onto ITO coated glass substrates by sol–gel method. TiO₂ nano flowers have been sensitized using CdS quantum dots prepared using simple precursors by chemical method. The assembly of CdS quantum dots with TiO₂ nano flower has been used as photo-electrode in quantum dot sensitized solar cells. The surface morphology has been studied using scanning electron microscope; it shows that the film exhibits flower like structure. The absorption spectra reveals that the absorption edge of CdS quantum dot sensitized TiO₂ nano flower shifts towards longer wavelength side when compared to the absorption edge of TiO₂ nano flower. The efficiency of the fabricated CdS quantum dot sensitized TiO₂ nano flower based solar cell is 0.66%.     

Three novel high performance affinity chromatographic media for the separation of antithrombin III from human plasma.

Novel monodisperse, non-porous, cross-linked poly (glycidyl methacrylate) beads (PGMA) were employed as the support for high performance affinity chromatography. Heparin was covalently attached to PGMA beads by three different coupling methods. Heparin-PGMA-I was prepared by directly coupling amino-groups of heparin with PGMA. Heparin-PGMA-II and III were prepared by the coupling of heparin to amino-PGMA, which was obtained by amination of PGMA. Heparin-PGMA-II was prepared by coupling the carboxyl groups of heparin to amino-PGMA by using water-soluble carbodiimide as coupling reagent, and heparin-PGMA-III was prepared by the reductive amination of heparin and amino-PGMA with sodium cyanoborohydride. The heparin contents of heparin-PGMA-I, II and III were 1.6, 10.2 and 1.0 mg/g beads, respectively. Their affinity capacities for antithrombin III were investigated. Their binding activity to antithrombin III was not proportional to the content of heparin immobilized, and heparin-PGMA-I was the most efficient affinity medium for antithrombin III. The resultant affinity media presented minimal non-specific interaction with other proteins and can be used in a wide pH range. All the three heparin-PGMA beads were exploited for the separation of antithrombin III from human plasma. The purity of antithrombin III obtained was higher than 90%, which was confirmed by high performance size exclusion chromatography.     

Electrically driven self‐healing polymers based on reversible guest–host complexation of β‐cyclodextrin and ferrocene

A multifunctional ferrocene‐modified poly(glycidyl methacrylate) (PGMA‐Fc) and a difunctional β‐cyclodextrin derivative (bis‐CD) has been prepared for the construction of an electrically driven removable and self‐healing polymeric materials based on the complexation reaction between ferrocene and β‐CD groups. The chemical structures of PGMA‐Fc and bis‐CD have been characterized with Fourier transform infrared, ¹H nuclear magnetic resonance, and X‐ray photoelectron spectroscopy. The effects of electrical voltages and medium conductivity on the decrosslinking efficiency of the crosslinked PGMA‐Fc/CD polymer have been examined. The PGMA‐Fc/CD network has shown removable feature and properties for application as a reworkable crosslinked material. Moreover, the crosslinked PGMA‐Fc/CD sample has shown electrically driven self‐healing behavior. The self‐healing performance could be enhanced with wetting the sample to increase the electrical conductivity. As a result, the material could serve as a self‐healing agent for commercial painting products. Preparation and application of a novel and efficient self‐healing polymer have been demonstrated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3395–3403     

Easily prepared high-quantum-yield CdS quantum dots in water using hyperbranched polyethylenimine as modifier

Some research has reported interaction between polyamidoamine dendrimers or polyethylenimine and quantum dots causing a quantum yield decrease of quantum dots. In this work, however, polyethylenimines of different molecular weight that were used to modify CdS quantum dots gave rise to the enhancement of CdS quantum yield to nearly 100%. Herein, we present the synthesis of a kind of easily prepared high-quantum-yield CdS quantum dot in aqueous solution and the study of the interaction between CdS and polyethylenimine.     

CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe<Superscript>−</Superscript> ions in aqueous solution

Water-soluble cadmium sulfide (CdS) quantum dots (QDs) capped by mercaptoacetic acid were synthesized by aqueous-phase arrested precipitation, and characterized by transmission electron microscopy, spectrofluorometry, and UV-Vis spectrophotometry. The prepared luminescent water-soluble CdS QDs were evaluated as fluorescence probes for the detection of highly reactive hydrogen selenide ions (HSe⁻ ions). The quenching of the fluorescence emission of CdS QDs with the addition of HSe⁻ ions is due to the elimination of the S²⁻ vacancies which are luminescence centers. Quantitative analysis based on chemical interaction between HSe⁻ ions and the surface of CdS QDs is very simple, easy to develop, and has demonstrated very high sensitivity and selectivity features. The effect of foreign ions (common anions and biologically relevant cations) on the fluorescence of the CdS QDs was examined to evaluate the selectivity. Only Cu²⁺ and S²⁻ ions exhibit significant effects on the fluorescence of CdS QDs. With the developed method, we are able to determine the concentration of HSe⁻ ions in the range from 0.10 to 4.80 μmol L⁻¹, and the limit of detection is 0.087 μmol L⁻¹. The proposed method was successfully applied to monitor the obtained HSe⁻ ions from the reaction of glutathione with selenite. To the best of our knowledge, this is the first report on fluorescence analysis of HSe⁻ ions in aqueous solution. Figure CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe- ions in aqueous solution     

Copper‐Doped CdSe/ZnS Quantum Dots: Controllable Photoactivated Copper(I) Cation Storage and Release Vectors for Catalysis

The first photoactivated doped quantum dot vector for metal‐ion release has been developed. A facile method for doping copper(I) cations within ZnS quantum dot shells was achieved through the use of metal‐dithiocarbamates, with Cu⁺ ions elucidated by X‐ray photoelectron spectroscopy. Photoexcitation of the quantum dots has been shown to release Cu⁺ ions, which was employed as an effective catalyst for the Huisgen [3+2] cycloaddition reaction. The relationship between the extent of doping, catalytic activity, and the fluorescence quenching was also explored.     

Analytical Applications of Enzymatic Growth of Quantum Dots

We have developed an analytical assay to detect the enzymatic activity of acetylcholine esterase and alkaline phosphatase based on the generation of quantum dots by enzymatic products. Acetylcholine esterase converts acetylthiocholine into thiocholine. The latter enhances the rate of decomposition of sodium thiosulfate into H₂S, which in the presence of cadmium sulfate yields CdS quantum dots showing a time dependent exponential growth, typical of autocatalytic processes. This assay was also applied to detect acetylcholine esterase inhibitors. Alkaline phosphatase hydrolyzes thiophosphate and yields H₂S, which instantly reacts with Cd²⁺ to give CdS quantum dots. The formation of CdS quantum dots in both reactions was followed by fluorescence spectroscopy and showed dependence on the concentration of enzyme and substrate.     

Determination of silver ion with cadmium sulfide quantum dots modified by bismuthiol II as fluorescence probe

CdS quantum dots (QDs) modified with bismuthiol II potassium salt is prepared in one step. Based on the characteristic fluorescence enhancement of CdS QDs at 480 nm by silver ions, simultaneously, a red shift of fluorescence emission bands of CdS QDs from 460 to 480 nm is observed. A simple, rapid, sensitive and specific detection method for silver ion is proposed. Under optimum conditions, the fluorescence intensity of CdS QDs was linearly proportional to silver ion concentration from 0.01 to 5.0 micromol L(-1) with a detection limit of 1.6 nmol L(-1). In comparison with single organic fluorophores, functionalized CdS quantum dots are brighter, more stable against photobleaching and do not suffer from blinking. Furthermore, the proposed method shows higher sensitivity and selectivity. A possible fluorescence enhancement mechanism is also studied.