In situ quantum dot growth on multiwalled carbon nanotubes

The generation of nanoscale interconnects and supramolecular, hierarchical assemblies enables the development of a number of novel nanoscale applications. A rational approach toward engineering a robust system is through chemical recognition. Here, we show the in situ mineralization of crystalline CdTe quantum dots on the surfaces of oxidized multiwalled carbon nanotubes (MWNTs). We coordinate metallic precursors of quantum dots directly onto nanotubes and then proceed with in situ growth. The resulting network of molecular-scale "fused" nanotube-nanocrystal heterojunctions demonstrates a controlled synthetic route to the synthesis of complex nanoscale heterostructures. Extensive characterization of these heterostructures has been performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-visible spectroscopy, and X-ray diffraction (XRD).     

A novel density-tunable nanocomposites of CdTe quantum dots linked to dendrimer-tethered multi-wall carbon nanotubes

A novel nanocomposite of CdTe–PAMAM–MWNT was synthesized by covalently linking CdTe quantum dots (QDs) onto highly water-soluble multi-wall carbon nanotubes (MWNTs) functionalized with dendritic poly(amidoamine) (PAMAM). The IR, UV–vis and TEM methods has been used for the characterization of the composites. A facile method for controlling the density of QDs in the composite by simply changing the ratio of CdTe QDs/PAMAM–MWNT, as was verified by the TEM images. The experiments revealed that PAMAM and PAMAM–MWNT, once covalently linked with CdTe QDs, had remarkable effect on their fluorescence property. The fluorescence intensity of the CdTe–PAMAM hybrid was substantially enhanced as a compared to that of QDs, and the fluorescence was quenched greatly when QDs reacted with PAMAM–MWNT. The experimentally observed phenomena indicate that electron and energy transfer took place efficiently between CdTe QDs, PAMAM and MWNTs in the novel composite. These nanocomposits might hold great potential in photoelectron device and biotechnology applications.     

Electrochemiluminescent sensing of dopamine using CdTe quantum dots capped with thioglycolic acid and supported with carbon nanotubes

We have synthesized water-dispersible CdTe quantum dots (QDs) capped with thioglycolic acid. Their quantum yield is higher than 54%. A sensitive electrochemiluminescence (ECL) method was established based on the modification of the composite of the QDs, carbon nanotubes and chitosan on indium tin oxide glass. The sensor displays efficient and stable anodic ECL which is quenched by dopamine. A respective sensor was designed that responds to dopamine linearly in the range of 50?pM to 10?nM, and the detection limit is 24?pM. Dopamine was determined with this sensor in spiked cerebro-spinal fluid with average recoveries of 95.7%.

Electrodeposition of Platinum Nanoparticles on Multi-Walled Carbon Nanotubes for Electrocatalytic Oxidation of Methanol

Platinum (Pt) nanoparticles were deposited at the surface of well-aligned multi-walled carbon nanotubes (MWNTs) by potential cycling between +0.50 and −0.70 V at a scanning rate of 50 mV · s⁻¹ in 5 mM Na₂PtCl₆ solution containing 0.1 M NaCl. The electrocatalytic oxidation of methanol at the nanocomposites of Pt nanoparticles/nanotubes (Pt_nano/MWNTs) has been investigated using 0.2 M H₂SO₄ as supporting electrolyte. The effects of various parameters, such as Pt loading, concentration of methanol, medium temperature as well as the stability of Pt_nano/MWNTs electrode, have been studied. Compared to glassy carbon electrode, carbon nanotube electrode significantly enhances the catalytic efficiency of Pt nanoparticles for methanol oxidation. This improvement in performance is due not only to the high surface area and the fast electron transfer rate of nanotubes but also to the highly dispersed Pt nanoparticles as electrocatalysts at the tips and the sidewalls of nanotubes.     

Signal Amplification Strategy Based on TiO2-Nanotube Layers and Nanobeads Carrying Quantum Dots for Electrochemiluminescent Immunosensors

Self-organized TiO₂-nanotube layers can be used for immunoassay-type sensing in combination with amplifying CdTe labels in a direct and very sensitive electrochemiluminescent (ECL) configuration. Key properties for this method are the conductivity of the TiO₂ nanotubes, and their transparency for light emitted from the CdTe labels at approximately 2.4 eV. To demonstrate the potential of this platform, we constructed a sandwich-type immunoassay onto the TiO₂-nanotube wall with a layer of (3-aminopropyl)triethoxysilane as the cross-linker for antibody immobilization. For the counter part of the sandwich, we created an amplification system consisting of TiO₂ nanobeads carrying the secondary antibody and multiple CdTe quantum dots (multiQD). For antigen (IgG) detection, we find that this combination of 3D transparent electrode with multiQD labels allows for an ECL detection limit of 0.05 pg mL⁻¹ and a linearity of the signal in the range of 0.1–10⁸ pg mL⁻¹.     

One-pot synthesis of strongly luminesencing CdTe quantum dots and their conjugation with mouse antibody to alpha-fetoprotein

In this paper, strongly luminescent CdTe quantum dots (QDs) were synthesized in aqueous solution by a facile one-pot method. The CdTe QDs were synthesized in a weakly acidic or neutral buffer solution composed of sodium borate (Na₂B₄O₇) and sodium citrate (C₆H₅Na₃O₇). The pH of buffer solution and the ratio of the precursors were systematically optimized; the high-quality CdTe QDs with progressively increasing fluorescence during 60 days storage were obtained. As-prepared QDs can be conjugated with a mouse antibody alpha-fetoprotein via the reaction mediated by N-hydroxysuccinimide and 1-ethyl-3(3-dimethylaminopropyl) carbodiimide hydrochloride. The conjugate showed a red shift of 9 nm for the emission position.     

Preparation and characterization of carbon nanotubes-polymer/CdSe hybrid nanocomposites through combining electrostatic adsorption and ATRP technique

This paper describes a new strategy through noncovalent functionalization of multi-walled carbon nanotubes (MWNTs) by a kind of new copolymer Polyethyleneimine-graft-Polyacrylonitrile for attaching CdSe nanoparticles onto the MWNTs to fabricate Carbon Nanotube/CdSe heterostructures. Polyethyleneimine (PEI), an amino-rich cationic polyelectrolyte, can interact with the MWNTs through electrostatic interaction. Then, CNT/PEI-g-PAN was successfully prepared by in situ atom transfer radical polymerization (ATRP), which did not introduce defects to the structure of CNTs. Thus, CdSe nanoparticles can be covalently coupled to functionalized carbon nanotubes (CNTs) in a uniform and controllable manner. Moreover, this method ensures good dispersion and high stability in any commonly used organic or inorganic solvent. In this manner, our strategy allows the attachment of various colloidal nanoparticles to CNTs, independent of their surface properties, i.e. hydrophilic or hydrophobic. TEM, XRD, EDS and FT-IR are all used to characterize the CNT/CdSe composite materials. In addition, the optical properties are investigated by UV–vis spectrum.     

<Emphasis Type="Italic">In silico</Emphasis> study of the atomic and electronic structure of quantum dots of the CdTe family doped with atoms of rare earth elements

An in silico study of semiconductor quantum dots of the CdTe family doped with atoms of rare earth elements is performed based of density functional theory. An ab initio computer design of quantum dots based on CdTe nanoparticles doped with Eu и Gd atoms is carried out. Partial densities of states of CdTe:Eu and CdTe:Gd quantum dots are calculated and analyzed. X-ray absorption near edge (XANES) spectra near the Eu K-, L₁-, and L₃- and Gd K-, L₁-, and L₃-edges of CdTe:Eu and CdTe:Gd quantum dots are calculated. The sensitivity of XANES spectroscopy for the verification of parameters of a nanosized atomic structure of quantum dots based on CdTe particles doped with atoms of rare earth elements and the determination of the local atomic structure around the atoms of rare earth elements in quantum dots is demonstrated.     

Facile synthesis of multifunctional multiwalled carbon nanotubes/Fe3O4 nanoparticles/polyaniline composite nanotubes

With an average diameter of 100-150 nm, composite nanotubes of polyaniline (PANI)/multiwalled carbon nanotubes (MWNTs) containing Fe₃O₄ nanoparticles (NPs) were synthesized by a two-step method. First, we synthesized monodispersed Fe₃O₄ NPs (d=17.6 nm, σ=1.92 nm) on the surface of MWNTs and then decorated the nanocomposites with a PANI layer via a self-assembly method. SEM and TEM images indicated that the obtained samples had the morphologies of nanotubes. The molecular structure and composition of MWNTs/Fe₃O₄ NPs/PANI nanotubes were characterized by Fourier transform infrared spectra (FTIR), energy dispersive X-ray spectrometry (EDX), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and Raman spectra. UV-vis spectra confirmed the existence of PANI and its response to acid and alkali. As a multifunctional material, the conductivity and magnetic properties of MWNTs/Fe₃O₄ NPs/PANI composites nanotubes were also investigated.     

Electroanalysis of Dopamine at RuO2 Modified Vertically Aligned Carbon Nanotube Electrode

Electrochemical behavior of dopamine at the RuO₂‐modified vertically aligned carbon nanotubes electrode was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The RuO₂‐modified carbon nanotube electrode showed higher electrocatalytic activity towards the oxidation of dopamine than the MWNTs electrode in 0.10 M phosphate buffer solution. At an applied potential of +0.4 V, the RuO₂/MWNTs electrode exhibited a wide detection range up to 3.6×10^?3 M with detection limit of 6.0×10^?8 M (signal/noise=3) for dopamine determination. Meanwhile, the optimized sensor for dopamine displayed a sensitivity of 83.8 μA mM^?1 and response time of 5 s with addition of 0.20 mM dopamine. In addition, DPV experiment revealed that interfering species such as ascorbic acid and uric acid could be effectively avoided. The RuO₂/MWNTs electrode presents stable, highly sensitive, favorable selectivity and fast amperometric response of dopamine.     

Simple Cast-Deposited Multi-Walled Carbon Nanotube/Nafion™ Thin Film Electrodes for Electrochemical Stripping Analysis

A stable composite film of multi-walled carbon nanotubes (MWNTs) with a Nafion™ cation exchanger membrane is prepared using a simple and reproducible cast deposition methodology. The MWNTs are cylindrical with diameters in the range of 40–60 nm and a length of up to several micrometers. They provide sufficiently high electrical conductivity across the film. Nafion™ acts both as a binder for the carbon structure and selectivity introducing matrix as shown by voltammetric experiments with the Fe(CN)₆^3−/4− redox system.The anodic stripping responses for Cd and Pb metal accumulated from a solution of 0.2–1 µM in 0.1 M acetate buffer are demonstrated and optimized. The limit of detection under these conditions is typically 51 nM. The feasibility of using the MWNTs/Nafion™ thin film electrode for the anodic stripping voltammetric determination of cadmium and lead in 0.1 M acetate buffer in the presence of surfactants/interferents is examined. Sodium dodecyl sulfate (SDS), Triton X-100 (TX-100), dodecyl pyridinium chloride (DPC), and bovine serum albumin (BSA) were examined as four typical interferents. Relatively small enhancing and suppressing effects on the stripping peak currents for Cd and for Pb detection at the MWNTs/Nafion™ film modified electrode were observed. The MWNTs/Nafion™ thin film electrode performed very well even in the presence of the cationic surfactant DPC and could in future be of wider applicability.     

Noncovalent functionalization of multiwalled carbon nanotubes: application in hybrid nanostructures

We developed a reproducible, noncovalent strategy to functionalize multiwalled carbon nanotubes (MWNTs) via embedding nanotubes in polysiloxane shells. (3-Aminopropyl)triethoxysilane molecules adsorbed to the nanotube surfaces via hydrophobic interactions are polymerized simply by acid catalysis and form a thin polysiloxane layer. On the basis of the embedded MWNTs, negatively charged gold nanoparticles are anchored to the nanotube surfaces via electrostatic interactions between the protonated amino groups and the gold nanoparticles. Furthermore, these gold nanoparticles can further grow and magnify along the nanotubes through heating in HAuCl4 aqueous solution at 100 degrees C; as a result these nanoparticles are joined to form continuous gold nanowires with MWNTs acting as templates.     

Electrochemiluminescence biosensor for Ramos cells based on a nanostructured conducting polymer composite material (PICA‐MWNTs)

A novel nanostructured conducting polymer (PICA‐MWNTs) is easily prepared by direct electrodeposition of indole‐6‐carboxylic acid (ICA) and carboxylic groups ended multiwalled carbon nanotubes (MWNTs) in acetonitrile in one step. The resulting PICA‐MWNTs composites with larger specific surface area and quite a few functionalized carboxylic acid groups are naturally integrated as a continuous uniform film on the electrode. CdSe quantum dots electrochemiluminescence biosensor with high sensitivity for detection of Ramos cells is fabricated based on PICA‐MWNTs. Coupled with nanoparticle‐amplification technnique, this sensor shows high sensitivity and good selectivity for Ramos cells with a low detection limit of 390 cells mL^?1. This result provides an avenue for a simple and sensitive approach for detection of Ramos cells, which may have great potential in clinical applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2385–2392     

镍铁氧体/碳纳米管复合材料的制备及其对染料废水的吸附性能

用浸渍法制备了镍铁氧体/碳纳米管(NF/MWNTs)复合材料。用XRD、SEM、TEM、VSM、UV-Vis等表征了样品的组成、结构、形貌、磁性能和吸附性能。结果表明,制备的NF/MWNTs复合材料保留了碳纳米管优良的吸附性能,且具有良好的镍铁氧体负载率和优异的磁性能。质量比(mNF/mMWNTs)为1的NF/MWNTs复合材料对亚甲基蓝溶液的最大吸附容量为18.87 mg·g-1,其吸附行为符合Langmuir和Freundlich模型。NF/MWNTs复合材料对亚甲基蓝溶液的脱色率与溶液温度和pH值呈正相关性。此外,NF/MWNTs复合材料回收容易,活化处理简便,可重复使用。     

镍铁氧体/碳纳米管复合材料的制备及其对染料废水的吸附性能

用浸渍法制备了镍铁氧体/碳纳米管(NF/MWNTs)复合材料。用XRD、SEM、TEM、VSM、UV-Vis等表征了样品的组成、结构、形貌、磁性能和吸附性能。结果表明,制备的NF/MWNTs复合材料保留了碳纳米管优良的吸附性能,且具有良好的镍铁氧体负载率和优异的磁性能。质量比(mNF/mMWNTs)为1的NF/MWNTs复合物对亚甲基蓝溶液的最大吸附容量为18.87mg·g^-1,其吸附行为符合Langmuir和Freundlich模型。NF/MWNTs复合材料对亚甲基蓝溶液的脱色率与溶液温度和pH值呈正相关性。此外,NF/MWNTs复合材料回收容易,活化处理简便,可重复使用。     

Laser-induced pinpoint hydrogen evolution from benzene and water using metal free single-walled carbon nanotubes with high quantum yields

Metal-free photocatalytic hydrogen evolution occurred efficiently in benzene containing single-walled carbon nanotubes under laser irradiation at 532 nm with an extremely high turnover number of 2 000 000 and a high quantum yield of 130%. The rate of hydrogen evolution increased with increasing laser intensity to exhibit a fourth power dependence, suggesting that hydrogen was evolved via four-photon processes in which the coupling of two radical anions derived from benzene is the rate-determining step and the benzene radical anion is produced by electron transfer from benzene to the doubly excited state of single-walled carbon nanotubes, which requires two photons. Polymerisation of benzene was induced by the photogenerated C₆H₆˙^–, accompanied by hydrogen evolution, resulting in a leverage effect to increase the quantum yield of hydrogen evolution to well over the 25% expected for the four-photon process. Laser-induced hydrogen evolution also occurred in water containing single-walled carbon nanotubes. In contrast to the case of benzene, water was not oxidized but hydrogen evolution from water was accompanied by the multi-oxidation of single-walled carbon nanotubes. The yield of hydrogen based on one mole of single-walled carbon nanotubes with 1.4 nm diameter and 1–5 mm length was determined to be 2 700 000%, when oxidations of single-walled carbon nanotubes occurred to produce the polyhydroxylated product.     

荧光碳点的合成及对酿酒酵母的毒性研究

以葡萄糖为碳源采用溶剂热法合成了荧光碳点。紫外吸收光谱、荧光光谱以及透射电镜照片表明,所合成的荧光碳点发光性能优异,分散性好,且无团聚现象。荧光碳点原溶液出现浓度淬灭现象,稀释60倍情况下荧光最强。以酿酒酵母为模型生物,考察了不同生长时期(调整期、对数期早期、对数期中期)的酿酒酵母与不同浓度的荧光碳点共培养后的生长曲线。结果表明,即使荧光碳点浓度在27.75 mmol.L-1条件下也没有影响酵母菌的生长曲线,可认为基本没有细胞毒性。比较了相同荧光强度下的荧光碳点与CdTe量子点对酿酒酵母的细胞毒性,结果表明荧光碳点的毒性显著低于量子点的毒性。     

有机相CdTe量子点/铕/聚甲基丙烯酸甲酯复合体系的发光性质

以十二烷基硫醇为稳定剂,在有机相中合成了平均粒径为4.5 nm的有机相CdTe量子点。 以三异丙氧基铕,有机相CdTe量子点为原料,用本体聚合反应得到的聚甲基丙烯酸甲酯作聚合物介质,将量子点与聚合物溶液或稀土铕离子、量子点与聚合物溶液分别通过范德华力或离子配位作用直接复合,分别得到CdTe/聚甲基丙烯酸甲酯和CdTe/铕/聚甲基丙烯酸甲酯。 采用红外光谱、紫外光谱、荧光光谱、扫描电子显微镜、透射电子显微镜对其结构进行表征。 结果表明,复合得到的CdTe量子点/聚甲基丙烯酸甲酯的溶液或薄膜在紫外到可见光区激发下均能发出很亮的红光,当稀土铕离子同时与量子点直接复合到聚合物中时,聚合物的溶液和薄膜仍可以发出量子点的发光,但其荧光相对强度下降,说明稀土铕离子与CdTe量子点的发光均由于它们之间的相互作用而猝灭。     

Electrochemiluminescence of CdSe Quantum Dots Composited with Nitrogen‐Doped Carbon Nanotubes

A nanocomposite of CdSe quantum dots with nitrogen‐doped carbon nanotubes was prepared for enhancing the electrochemiluminescent (ECL) emission of quantum dots. With hydrogen peroxide as co‐reactant, the nanocomposite modified electrode showed a cathodic ECL emission with a starting potential of ?0.97 V (vs. Ag/AgCl) in phosphate buffer solution, which was five‐times stronger than that from pure CdSe quantum dots and three‐times stronger than that from CdSe quantum dots composited with carbon nanotubes. The latter showed a starting potential of ?1.19 V. This result led to a sensitive ECL sensing of hydrogen peroxide with good stability, acceptable reproducibility and a detection limit down to 2.1×10^?7 mol L^?1. Nitrogen‐doped carbon nanotubes could be used as a good material for the construction of sensitive ECL biosensors for chemical and biochemical analysis.     

Carbon nitride nanotubulite – densely-packed and well-aligned tubular nanostructures

Tubular carbon nitride (CN_x, x=0.01–0.32) nanoparticles were successfully synthesized by d.c. magnetron sputtering. These tubes were grown in a highly packed form perpendicularly on a sodium chloride substrate. Their number density is estimated to be 1×10⁴ per μm² and is constant over macroscopic regions. Sub-nanometer scale chemical mapping shows that the nitrogen to carbon atomic ratio is rather constant across these tubes. This successful synthesis of a nanotubulite – made of a rather compact aggregation of tubular nanoparticles – could facilitate experimental approaches to measure mechanical or electrical transport properties of such nanotubes and to open the way to variable nanotube applications.