Construction of CdS quantum dots via a regioselective dendritic functionalized cellulose template

Using regioselective dendritic functionalized cellulose, CdS quantum dot nanoparticles were prepared and their photo-optical properties and morphology as well as the preliminary biocompatibility of the hybrid were investigated.     

Preparation of ultrasmall, uncapped PbS quantum dots via electroporation of vesicles

Electric-field-induced transient pore formation (electroporation) in synthetic unilamellar dioleoylphosphatidylcholine vesicles of 178-nm diameter is utilized for the preparation of subnanometer-size PbS quantum dots. With Pb2+ ions originally entrapped in the vesicles and S2- ions placed in the bulk, their reaction is initiated by the opening of pores and occurs in the bulk. The ensuing self-aggregation of PbS is slowed to the hour and day time scales by its adsorption at the exterior surface of the vesicles. The growth of the particles in the molecular size regime is found to exhibit novel, time-dependent, oscillating red and blue shifts of the characteristic UV absorption band. On the basis of similarities between the oscillating trend of the experimentally observed transition energy and that of the calculated highest occupied molecular orbital-lowest unoccupied molecular orbital gap of (PbS)n clusters with n = 1-9, the wavelengths of the sequential spectral peaks can be assigned to the PbS monomer (237.5 nm), dimer (282 nm), tetramer (232 nm), hexamer (281 nm), octamer (234.5 nm), and nonamer (278-280 nm). Growth beyond the octamer is associated with the customary monotonic red shift of the absorption band. Under the experimental conditions used, a stable system is reached with unchanging spectral features after 20 days. This solution is estimated to contain 1.82 x 10(-5) M (PbS)9 particles, each with a greatest dimension of <9 A.     

Preparation and properties of polymer/zinc oxide nanocomposites using functionalized zinc oxide quantum dots

Poly(methyl methacrylate) (PMMA)/zinc oxide (ZnO) or carbazole polymer (PCEM)/ZnO nanocomposites, which are composed of high molecular weight PMMA or PCEM with narrow molecular weight distributions and ZnO nanoparticles, were successfully prepared by atom transfer radical polymerization (ATRP) initiated by 2-bromo-2-methylpropionyl (BMP) group (ZnBM) introduced onto the ZnO nanoparticle surfaces. Introduction of the BMP group onto the ZnO surfaces was achieved by esterification of OH group of the ZnO surfaces. The chemically attached OH group-having ZnO nanoparticles (ZnHM) were fabricated by sol-gel reaction from zinc acetate dihydrate, followed by treatment of the ZnO nanoparticles with 2-hydroxypropionic acid (HPA). The ZnHM nanoparticles showed one UV absorption and two emission bands: UV emission peak and broad visible emission band, while the ZnBM exhibited broad UV absorption and no emission spectra. The PMMA/ZnO nanocomposites displayed UV absorption and photoluminescent (PL) band with blue emission on the basis of the ZnHM nanoparticles, where the ZnO nanoparticles dispersed homogeneously in the PMMA matrix. The PCEM/ZnO nanocomposites depicted UV emission peak due to the carbazole unit in the UV range, but no visible emission. Thermal properties of the PMMA/ZnO nanocomposites were improved by dispersion of the ZnO nanoparticles into the PMMA, but the PCEM/ZnO nanocomposites showed no improvement of the thermal properties.     

Biomimetic interactions of proteins with functionalized cadmium sulfide quantum dots

Interactions between various modified semiconductor nanocrystal, cadmium sulfide quantum dots (CdS QDs) and bovine serum albumin (BSA) and lysozyme (LZY) were investigated. CdS QDs capped with mercaptoethanol (MPA), l-cysteine (Lcys) and glutathione (GSH) were synthesized in aqueous solution and characterized by UV-vis and fluorescence spectrum. Circular dichroism (CD) and fluorescence spectrum were used to detect the interactions between as-prepared CdS QDs and protein molecules. The interaction parameters, including binding constant (K_b), binding site number (n) and quench constant (K_q), were determined by fluorescence spectrum. The changes of secondary structures of the proteins were detected by CD. The results imply that CdS QDs modified by different agents have dramatically different binding strength with protein molecules. The results obtained here analyze the biosafety of CdS QDs in terms of the biological behavior of biomolecules and could serve as basis for the application of CdS QDs to bioscience.     

Stable functionalized PEGylated quantum dots micelles with a controlled stoichiometry

Here we report the synthesis of monofunctional PEGylated amide ligands that were used to prepare bioactivable quantum dots of a 20 nm diameter with a controlled mean number of the covalently grafted ligands. They are stable in aqueous medium of high salinity including a large pH domain.     

Cytoplasmic delivery of quantum dots via microelectrophoresis technique

Nanoparticles with specific properties and functions have been developed for various biomedical research applications, such as in vivo and in vitro sensors, imaging agents and delivery vehicles of therapeutics. The development of an effective delivery method of nanoparticles into the intracellular environment is challenging and success in this endeavor would be beneficial to many biological studies. Here, the well-established microelectrophoresis technique was applied for the first time to deliver nanoparticles into living cells. An optimal protocol was explored to prepare semiconductive quantum dots suspensions having high monodispersity with average hydrodynamic diameter of 13.2–35.0 nm. Micropipettes were fabricated to have inner tip diameters of approximately 200 nm that are larger than quantum dots for ejection but less than 500 nm to minimize damage to the cell membrane. We demonstrated the successful delivery of quantum dots via small electrical currents (–0.2 nA) through micropipettes into the cytoplasm of living human embryonic kidney cells (roughly 20–30 μm in length) using microelectrophoresis technique. This method is promising as a simple and general strategy for delivering a variety of nanoparticles into the cellular environment.     

La掺杂ZnS量子点的制备及其表征

ZnS量子点的发光强度较弱,用水相合成技术掺杂一定浓度的La3+可以增强其发光性能。本文以实验用N-乙酰-L-半胱氨酸作保护剂,Zn(Ac)2作锌源,Na2S作硫源、La(Ac)3作镧源合成La掺杂的ZnS量子点,并通过透射电镜(TEM)和X-射线粉末衍射(XRD)对其物相进行了表征。紫外-可见(UV-Vis)及荧光(PL)光谱性质亦进行了表征。     

Multi-analyte homogenous immunoassay based on quenching of quantum dots by functionalized graphene

We propose a homogenous multi-analyte immunoassay based on the quenching of quantum dot (QD) fluorescence by means of graphene. Two QDs with emission maxima at 636 and 607 nm were bound to antibodies selective for mouse or chicken immunoglobulins, respectively, and graphene functionalized with carboxylic moieties was employed to covalently link the respective antigen. The antibody-antigen interaction led graphene close enough to QDs to quench the QD fluorescence by resonance energy transfer. The addition of free antigens that competed with those linked to graphene acted as a “turn-on” effect on QD fluorescence. Fluorescence emitted by the two QDs could be recorded simultaneously since the QDs emitted light at different wavelengths while being excited at the same wavelength and proved to be linearly correlated with free antigen concentration. The developed assay allows measuring both antigens over 2–3 orders of magnitude and showed estimated limits of detection in the nanomolar range. This approach is thus a promising universal strategy to develop homogenous immunoassays for diverse antigens (cells, proteins, low-molecular-mass analytes) in a multi-analyte configuration.     

Biotin-modified glutathione as a functionalized coating for bioconjugation of CdTe-based quantum dots

In this study, biotin-conjugated glutathione was synthesized using peptide bonding of the biotin carboxy group and amino group of the γ-glutamic acid to prepare an alternative coating for CdTe quantum dots (QDs). This type of coating combines the functionality of the biotin with the fluorescent properties of the QDs to create a specific, high-affinity fluorescent probe able to react with avidin, streptavidin and/or neutravidin. Biotin-functionalized glutathione-coated CdTe QDs were prepared by a simple one-step method using Na? TeO? and CdCl?. Obtained QDs were separated from the excess of the biotin-conjugated glutathione by CE employing 300?mM borate buffer with pH 7.8 as a background electrolyte. The detection of sample components was performed by the photometric detection at 214?nm and LIF employing Ar? ion laser (488?nm).     

Silica-coated CdTe quantum dots functionalized with thiols for bioconjugation to IgG proteins

Quantum dots (QDs) have been increasingly used in biolabeling recently as their advantages over molecular fluorophores have become clear. For bioapplications QDs must be water-soluble and buffer stable, making their synthesis challenging and time-consuming. A simple aqueous synthesis of silica-capped, highly fluorescent CdTe quantum dots has been developed. CdTe QDs are advantageous as the emission can be tuned to the near-infrared where tissue absorption is at a minimum, while the silica shell can prevent the leakage of toxic Cd(2+) and provide a surface for easy conjugation to biomolecules such as proteins. The presence of a silica shell of 2-5 nm in thickness has been confirmed by transmission electron microscopy and atomic force microscopy measurements. Photoluminescence studies show that the silica shell results in greatly increased photostability in Tris-borate-ethylenediaminetetraacetate and phosphate-buffered saline buffers. To further improve their biocompatibility, the silica-capped QDs have been functionalized with poly(ethylene glycol) and thiol-terminated biolinkers. Through the use of these linkers, antibody proteins were successfully conjugated as confirmed by agarose gel electrophoresis. Streptavidin-maleimide and biotinylated polystyrene microbeads confirmed the bioactivity and conjugation specificity of the thiolated QDs. These functionalized, silica-capped QDs are ideal labels, easily synthesized, robust, safe, and readily conjugated to biomolecules while maintaining bioactivity. They are potentially useful for a number of applications in biolabeling and imaging.     

Preparation and biodistribution of 131I-labeled graphene quantum dots

Uranium sorption from commercial phosphoric acid was carried out onto kaolinite and metakaolinite. The different factors affecting uranium adsorption have been investigated. The obtained results show that, the sorption process is applicable for the high strength phosphoric acid, 40% P₂O₅, and diluted phosphoric acid, 20% P₂O₅, but it preferred to the diluted phosphoric acid. The kinetic models applied to the sorption rate data were evaluated for Lagergren first order and the pseudo second order models. From the results, the uranium sorption from commercial phosphoric acid, 40% P₂O₅, onto kaolinite and metakaolinite was found to occur through physical sorption process.     

Sensitive detection of trace hemoglobin using fluorescence method based on functionalized quantum dots

The fluorescence quenching of quantum dots by hemoglobin has been demonstrated to depend on surface functionalization, and this property has been utilized to construct a novel fluorescent method for rapid, sensitive, and selective detection of trace hemoglobin in urine at microgram level. This method shows low interference and high selectivity for hemoglobin with a limit of detection of 4.3 μg L^?1 in water and 66.1 μg L^?1 in urine, which are lower than those of currently used methods in labs and clinics. Spike and recovery tests in raw, acidified, and alkalized urine samples exhibit good recovery rates for the spiked concentrations close to the limit of detection.

Subnanometer size uncapped quantum dots via electroporation of synthetic vesicles

The very rapid, usually diffusion-controlled, self-aggregation of nascent molecules of semiconductors (MX) or metals (M) in solution represents an experimental challenge for arresting the growth of the particles at a desired size. Unfortunately, the typical remedy used, namely capping of the clusters with a protective coating, alters their intrinsic electronic and optical properties. An additional defect of capping's virtue is that it prevents the observation of further cluster growth—which is especially important in the subnanometer (molecular) size regime, where particle growth is associated with dramatic changes in structure, surface states, and transition energy.

We have developed a novel method for the preparation of subnanometer size uncapped quantum dots, which also allows the monitoring of their growth up to several hundreds of nanometer in diameter. The essence of the method is the initial encapsulation of the metal ion (M⁺) in synthetic vesicles (liposomes) and the placement of the anion (X⁻) in the bulk solution. Exposure of the suspension to a rectangular pulse of a high-voltage homogenous electric field E of suitable intensity and duration causes the formation of transient pores in the vesicle's bilayer (electroporation). A fraction of the metal ions that are ejected through the pores react with the anions in the bulk, and the freshly created monomers (MX) adsorb on the exterior surface of the vesicle. On the vesicle surface, the self-aggregation is slowed down to the hour and day timescales which allows for convenient spectral monitoring of the growth of the clusters.

The discussion will focus on the behavior of vesicles in an electric field, the mechanism of electroporation, and our experimental and density functional theoretical findings of previously unobserved, unusual spectroscopic properties of subnanometer size AgBr, CdS, PbS, ZnS and gold quantum dots.     

Simple and accurate quantification of quantum dots via single-particle counting

Quantification of quantum dots (QDs) is essential to the quality control of QD synthesis, development of QD-based LEDs and lasers, functionalizing of QDs with biomolecules, and engineering of QDs for biological applications. However, simple and accurate quantification of QD concentration in a variety of buffer solutions and in complex mixtures still remains a critical technological challenge. Here, we introduce a new methodology for quantification of QDs via single-particle counting, which is conceptually different from established UV-vis absorption and fluorescence spectrum techniques where large amounts of purified QDs are needed and specific absorption coefficient or quantum yield values are necessary for measurements. We demonstrate that single-particle counting allows us to nondiscriminately quantify different kinds of QDs by their distinct fluorescence burst counts in a variety of buffer solutions regardless of their composition, structure, and surface modifications, and without the necessity of absorption coefficient and quantum yield values. This single-particle counting can also unambiguously quantify individual QDs in a complex mixture, which is practically impossible for both UV-vis absorption and fluorescence spectrum measurements. Importantly, the application of this single-particle counting is not just limited to QDs but also can be extended to fluorescent microspheres, quantum dot-based microbeads, and fluorescent nano rods, some of which currently lack efficient quantification methods.     

ZnO-离子液体功能化的石墨烯量子点的制备及荧光性能

利用水热法制备了ZnO-1-丙胺基-3-甲基咪唑氯离子液体功能化的石墨烯量子点溶液,通过紫外-可见吸收光谱、红外吸收光谱和透射电镜对其进行了表征.通过研究各种因素对ZnO-离子液体功能化的石墨烯量子点的荧光发射光谱的影响,发现Cr₂O₇^2-对ZnO-离子液体功能化的石墨烯量子点有荧光猝灭现象.实验结果表明,在优化的实验条件下,pH=5.0,Cr(Ⅵ)浓度为1.0×10^-7～1.6×10^-6 mol·L^-1时,Cr(Ⅵ)对ZnO-离子液体功能化的石墨烯量子点的荧光猝灭呈线性,其线性方程为F/F₀=0.969 5-0.008 4c,R=0.998 8,检出限为7.6×10^-2μmol·L^-1.     

Preparation of fullerene-polyyne nanospheres via thermally induced solid-state polymerization

A 1,3,5,7-octatetrayne-linked bis(fullerene) compound has been synthesized. Through a thermally induced solid-state polymerization reaction on a surface, the solid thin film of this compound was transformed into a highly uniform and well organized polymer nanosphere array. This finding suggests a simple and useful method for the preparation of carbon-rich, fullerene-containing nanoparticles.     

Organic-inorganic nanocomposites via directly grafting conjugated polymers onto quantum dots

Nanocomposites of poly(3-hexylthiophene)-cadmium selenide (P3HT-CdSe) were synthesized by directly grafting vinyl-terminated P3HT onto [(4-bromophenyl)methyl]dioctylphosphine oxide (DOPO-Br)-functionalized CdSe quantum dot (QD) surfaces via a mild palladium-catalyzed Heck coupling, thereby dispensing with the need for ligand exchange chemistry. The resulting P3HT-CdSe nanocomposites possess a well-defined interface, thus significantly promoting the dispersion of CdSe within the P3HT matrix and facilitating the electronic interaction between these two components. The photophysical properties of nanocomposites were found to differ from the conventional composites in which P3HT and CdSe QDs were physically mixed. Solid-state emission spectra of nanocomposites suggested the charge transfer from P3HT to CdSe QDs, while the energy transfer from 3.5 nm CdSe QD to P3HT was implicated in the P3HT/CdSe composites. A faster decay in lifetime further confirmed the occurrence of charge transfer in P3HT-CdSe nanocomposites.     

Synthesis of cationic quantum dots via a two-step ligand exchange process

A new class of quaternary ammonium derivatives has been used to synthesize cationic CdSe/ZnS quantum dots with exceptional stability in water as well as in biological media.     

微波辐射法制备水溶性CdTe/ZnS量子点及其与司帕沙星的作用

以巯基乙酸为稳定剂,通过微波加热在水溶液中制备了CdTe/znS量子点.研究了pH值、反应时间、反应温度和cdTe/s<'2->浓度比等合成条件对cdTe量子点荧光光谱的影响.以CdTe/ZnS量子点为探针,探讨了喹诺酮类抗生素司帕沙星与量子点的荧光猝灭作用,结果表明,在最佳实验条件下,其线性范围为0.05～3.00μg/mL,线性相关系数为0.9954,检出限为0.01μg/mL,可将CdTe/ZnS量子点荧光探针用于司帕沙星的测定.