Synthesis of SERS active Ag2S nanocrystals using oleylamine as solvent,reducing agent and stabilizer

Semiconductor Ag₂S nanocrystals have been prepared via a facile solution growth method, in which AgNO₃ and sulfur (S) powder are used as precursors, oleylamine is used and can function as both reducing agent and stabilizer during the synthetic process. The experimental results demonstrate that the as-synthesized Ag₂S nanocrystals, which have uniform size are monoclinic Ag₂S. Furthermore, surface-enhanced Raman scattering (SERS) spectrum of rhodamine 6G can be obtained on the Ag₂S nanocrystals modified substrate, indicating novel optical response of Ag₂S nanocrystals. The SERS effect of Ag₂S nanocrystals should attract much interest in fundamental physics as well as device application points of view.     

Preparation and characterization of gold nanoparticles using ascorbic acid as reducing agent in reverse micelles

In this study, well-dispersed gold nanoparticles were prepared by the reduction of HAuCl₄ in sodium bis(2-ethylhexyl)sulfosuccinate/isooctane reverse micelles system using ascorbic acid as reducing agent. The properties of the obtained nanoparticles were characterized with transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and UV–vis absorption spectrophotometer. Due to its high water solubility, biodegradability, and low toxicity, ascorbic acid could be used as a benign naturally available reducing agent to synthesize gold nanoparticles.     

Synthesis and optical properties of CdS nanorods and CdSe nanocrystals using oleylamine as both solvent and stabilizer

CdS nanorods and CdSe nanocrystals were prepared via the one-pot synthesis approach in oleylamine (OLA) system. The OLA used in this process as both the solvent and stabilizer is favorable for probing capping mechanism and simplifying experimental steps. The growth process and characterization of cadmium chalcogenide nanocrystals were determined by X-ray diffraction (XRD), transmission electron microscopy (TEM), Ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy. Results demonstrated OLA-capped CdS nanorods and CdSe nanocrystals were highly crystalline and had good optical properties.     

以次磷酸钠为还原剂涤纶织物化学镀铜研究

研究了采用次磷酸钠作还原剂在涤纶织物上化学镀铜.分别采用X射线衍射 (XRD) 、扫描电镜(SEM)和能谱议(EDAX)分析化学镀铜层的晶体结构、表面形貌和镀层成分.分别用四探针法(ASTM F 390) 和双轴传输线法(ASTM D 4935-99) 测量导电涤纶织物的表面电阻和电磁屏蔽效能.化学镀铜溶液的成分和操作条件对化学镀铜的沉积速度、镀层成分、结构和表面形貌具有重大的影响.化学镀铜的沉积速度随着温度、pH值和镍离子浓度的升高而加快,而且沉速度过快会导致镀层疏松.镍离子浓度的增加还导致镀层镍含量的增加从而使表面电阻明显增大.加入适量的亚铁氰化钾可以降低沉积速度,改善镀层结构和表面形貌,降低织物表面电阻.当Ni2 和K4Fe(CN)6浓度分别为0.0038mol/L和2×10-6时,可以获得最佳的化学镀铜层;当织物上铜镀层的重量为40g/m2时,在100MHz～20GHz频率范围内电磁屏蔽效能均可达到85dB以上.     

Preparation of gold nanoparticles in an aqueous medium using 2-mercaptosuccinic acid as both reduction and capping agent

Monolayer protected gold nanoparticles with diameters above 10 nm were prepared by a simple, one step reaction in water. 2-mercaptosuccinic acid (MSA) was used both as reduction agent for hydrogen tetrachloroaurate (HAuCl4) and as stabilizing agent for the gold nanoparticles. Size distribution and surface chemistry were investigated by UV-Vis spectroscopy, scanning electron microscopy and Fourier Transform Infrared Spectroscopy. Particle size can be controlled by adjusting the molar portions of the reactants. The resulting particles are efficiently stabilized against aggregation when MSA is used in a concentration of 40% and above. Below a minimum MSA concentration a long-term particle growth is observed.     

A single-step synthesis of gold nanochains using an amino acid as a capping agent and characterization of their optical properties

We demonstrated a simple single-step synthesis of gold nanochains by reducing aqueous chloroaurate ions (AuCl(4)(-)) with sodiumborohydride (NaBH(4)) in the presence of an amino acid (glutamic acid and histidine) as a stabilizer. The structure and optical properties of gold nanochains and nanowires were characterized by transmission electron microscopy, UV-visible spectroscopy, infrared spectroscopy and femtosecond z-scan measurements. The results suggested that the gold nanochains and nanowires were formed via the nanospheres fusing into one another by an oriented attachment mechanism through dipole-dipole interactions. The z-scan measurements on Au nanowires showed a transition from saturable absorption to reverse saturable absorption as the pump intensity increased.     

Shape and composition-controlled platinum alloy nanocrystals using carbon monoxide as reducing agent

The shape of metal alloy nanocrystals plays an important role in catalytic performances. Many methods developed so far in controlling the morphologies of nanocrystals are however limited by the synthesis that is often material and shape specific. Here we show using a gas reducing agent in liquid solution (GRAILS) method, different Pt alloy (Pt-M, M = Co, Fe, Ni, Pd) nanocrystals with cubic and octahedral morphologies can be prepared under the same kind of reducing reaction condition. A broad range of compositions can also be obtained for these Pt alloy nanocrystals. Thus, this GRAILS method is a general approach to the preparation of uniform shape and composition-controlled Pt alloy nanocrystals. The area-specific oxygen reduction reaction (ORR) activities of Pt(3)Ni catalysts at 0.9 V are 0.85 mA/cm(2)(Pt) for the nanocubes, and 1.26 mA/cm(2)(Pt) for the nanooctahedra. The ORR mass activity of the octahedral Pt(3)Ni catalyst reaches 0.44 A/mg(Pt).     

On the polyol synthesis of silver nanostructures: glycolaldehyde as a reducing agent

The polyol synthesis is a popular method of preparing metal nanostructures, yet the mechanism by which metal ions are reduced is poorly understood. Using a spectrophotometric method, we show, for the first time, that heating ethylene glycol (EG) in air results in its oxidation to glycolaldehyde (GA), a reductant capable of reducing most noble metal ions. The dependence of reducing power on temperature for EG can be explained by this temperature-dependent oxidation, and the factors influencing GA production can have a profound impact on the nucleation and growth kinetics. These new findings provide critical insight into how the polyol synthesis can be used to generate metal nanostructures with well-controlled shapes. For example, with the primary reductant identified, it becomes possible to evaluate and understand its explicit role in generating nanostructures of a specific shape to the exclusion of others.     

Effect of reducing agent on the synthesis of nickel nanoparticles

Synthesis of nickel nano-particles with a coating of a hydrophilic surfactant has been carried out by use of sodium borohydride and sodium formaldehyde sulfoxylate (SFS) in aqueous medium. It is observed that an ideal temperature range for formation of nickel nanoparticles is between 50 and 100 °C. Phase-pure nano-nickel can be obtained by use of SFS. X-ray diffraction measurements (XRD) revealed broad pattern for fcc crystal structure of nickel metal with particle diameter of about 10-15 nm. Scanning Electron Microscopy (SEM) showed that there is clustering of spherical particles in dry state and Transmission Electron Microscopy (TEM) gave a particle size of about less than 10 nm.     

A renewable electrochemical magnetic immunosensor based on gold nanoparticle labels

A particle-based renewable electrochemical magnetic immunosensor was developed by using magnetic beads and gold nanoparticle labels. Anti-IgG antibody-modified magnetic beads were attached to a renewable carbon paste transducer surface by magnet that was fixed inside the sensor. Gold nanoparticle labels were capsulated to the surface of magnetic beads by sandwich immunoassay. Highly sensitive electrochemical stripping analysis offers a simple and fast method to quantify the capatured gold nanoparticle tracers and avoid the use of an enzyme label and substrate. The stripping signal of gold nanoparticles is related to the concentration of target IgG in the sample solution. A transmission electron microscopy image shows that the gold nanoparticles were successfully capsulated to the surface of magnetic beads through sandwich immunoreaction events. The parameters of immunoassay, including the loading of magnetic beads, the amount of gold nanoparticle conjugate, and the immunoreaction time, were optimized. The detection limit of 0.02 microg ml(-1) of IgG was obtained under optimum experimental conditions. Such particle-based electrochemical magnetic immunosensors could be readily used for simultaneous parallel detection of multiple proteins by using multiple inorganic metal nanoparticle tracers and are expected to open new opportunities for disease diagnostics and biosecurity.     

Preparation of fine copper powder using ascorbic acid as reducing agent and its application in MLCC

The preparation of ultrafine copper powder with chemical reduction method was investigated. Ascorbic acid was employed as reducing agent. Reaction of CuSO₄·5H₂O with ascorbic acid at 70 °C gives polyhedron monodispersed ultrafine copper powder. The copper powder having excellent dispersibility was prepared when the pH value was controlled at 6 with aqueous ammonia. Influences of reaction temperature on the efficiency of copper powders were also studied. TG/DTG/DTA of copper powder was discussed with thermal analyzer. As-prepared copper powder was applied in BME-MLCC. The micro-structures of end termination and interface were discussed with SEM and polarized light microscope. The copper end termination has high adhesion force, excellent solderibility behavior and resistance behavior to soldering.     

A gold nanoparticle platform for protein-protein interactions and drug discovery

Gold nanoparticles hold great promise for studying protein-protein interactions because of their intrinsic optical properties. Pink when in a homogeneous suspension, the solution turns blue-gray when particles are drawn close together, for example, when immobilized proteins specifically interact with each other. However, the nanoparticle stability, size, and method of protein attachment contribute to the unreliable outcome of current assays. To overcome these hurdles, we developed novel and reliable methods first to synthesize homogenous particles of optimal diameter and second to apply a heterologous NTA-Ni-SAM coating for controlled orientation and optimal presentation of histidine-tagged proteins. Both methods were proven to greatly enhance assay sensitivity and specificity by increasing the signal and minimizing the nonspecific binding. Our assay reproducibly detected known protein-protein interactions and unambiguously identified small molecules that inhibited them. We believe our gold nanoparticle bioassay is a versatile and trustworthy new platform for analyzing protein-protein interactions and high-throughput screening of small-molecule inhibitors.     

CVD of Ru,Pt and Pt-based alloy thin films using ethanol as mild reducing agent

Noble metal thin films (Pt and Ru) were grown at 250 °C, using commercially available precursors, by the pulsed spray evaporation chemical vapor deposition (PSE-CVD) technique. The growth process relies on the thermally activated reaction of ethanol with the metal acetylacetonate precursors. The synthesized polycrystalline films are pure metal phase and crystallize in hexagonal (Ru) and cubic (Pt) structures. The formation of an interfacial silicide phase was noticed in the case of the Pt growth on silicon substrates. The films are smooth, continuous and show a steady growth without any noticeable incubation time. The single-step growth of Pt-based alloys, Pt–Co and Pt–Cu, with controlled composition was performed by simply adjusting the composition of the liquid feedstock.     

Palladium and gold nanoparticle array films formed by using self-assembly of block copolymer

The well-arrayed Pd and Au nanoparticle thin films were successfully prepared by making use of self-assembled PS-b-P4VP block copolymer (BCP) as a mask for the reduction of PdCl2 deposited on glass substrate. The films consisted of spherialcal nanoparticles with an average diameter of about 45 nm. For monitoring the size, shape and array formation of Pd nanopaticle films, this procedure was proved better to the conventional process in which PdCl2 impregnated in the channels of self assembled BCP film is reduced to form nanoparticle array. This observations of Pd nanoparticle array film formation is supported by the AFM and UV-VIS studies of Au nanoparticle array films formed by conventional method.     

Highly sensitive electrogenerated chemiluminescence biosensor in profiling protein kinase activity and inhibition using gold nanoparticle as signal transduction probes

A novel electrogenerated chemiluminescence (ECL) biosensor using gold nanoparticles as signal transduction probes was described for the detection of kinase activity. The gold nanoparticles were specifically conjugated to the thiophosphate group after the phosphorylation process in the presence of adenosine 59-[c-thio] triphosphate (ATP-s) cosubstrate. Due to its good conductivity, large surface area, and excellent electroactivity to luminol oxidization, the gold nanoparticles extremely amplified the ECL signal of luminol, offering a highly sensitive ECL biosensor for kinase activity detection. Protein kinase A (PKA), an important enzyme in regulation of glycogen, sugar, and lipid metabolism in the human body, was used as a model to confirm the proof-of-concept strategy. The as-proposed biosensor presented high sensitivity, low detection limit of 0.07 U mL(-1), wide linear range (from 0.07 to 32 U mL(-1)), and excellent stability. Moreover, this biosensor can also be used for quantitative analysis of kinase inhibition. On the basis of the inhibitor concentration dependent ECL signal, the half-maximal inhibition value IC(50) of ellagic acid, a PKA inhibitor, was estimated, which was in agreement with those characterized with the conventional kinase assay. While nearly no ECL signal change can be observed in the presence of Tyrphostin AG1478, a tyrosine kinase inhibitor, but not PKA inhibitor, shows its excellent performance in kinase inhibitor screening. The simple and sensitive biosensor is promising in developing a high-through assay of in vitro kinase activity and inhibitor screening for clinic diagnostic and drug development.     

A facile synthesis of silver nanoparticle with SERS and antimicrobial activity using Bacillus subtilis exopolysaccharides

In this study, we report a facile synthesis of silver nanoparticle having SERS and antimicrobial activity using bacterial exopolysaccharide (EPS). Bacillus subtilis (MTCC 2422) was grown in nutrient broth and the extracellular EPS secreted by the organism was extracted and purified. The purified EPS was used for the synthesis of silver nanoparticles. The kinetics of silver nanoparticle synthesis was deduced by varying the exposure time and the concentration of EPS. The rate constant (k) for the synthesis of silver nanoparticle was calculated from the slope of ln(A^∞ ? A^t) versus time plot. The k value was found to be 3.49 × 10^?3, 5.81 × 10^?3 and 5.03 × 10^?3 per min for particle synthesis using 2, 5 and 10 mg/mL EPS, respectively. The nanoparticles synthesised had an average particle size of 5.18 ± 1.49 nm, 1.96 ± 0.77 nm and 2.08 ± 0.88 nm for 2, 5 and 10 mg/mL EPS, respectively. The synthesised particles were characterised using UV-Vis absorbance spectroscopy, high-resolution transmission electron microscopy (HRTEM) attached to EDS (energy dispersive spectroscopy), Fourier transform infrared spectroscopy (FTIR), surface enhanced Raman spectroscopy (SERS) and zeta potential analyser. To our knowledge, this is the first study to report SERS activity of microbial Bacillus subtilis EPS-based synthesis of silver nanoparticle. HRTEM images showed silver nanoparticle entrapped in polysaccharide nanocages. Silver nanoparticle showed higher adherence towards the bacterial surface, with good bactericidal activity against Pseudomonas aeroginosa and Staphylococcus aureus.     

Energy transfer-based multiplexed assay of proteases by using gold nanoparticle and quantum dot conjugates on a surface

Rapid and sensitive assay of proteases and their inhibition in a high-throughput manner is of great significance in the diagnostic and pharmaceutical fields. We developed a multiplexed assay system of proteases and their inhibition by measuring the energy transfer between quantum dots (QDs) and gold nanoparticles (AuNPs) on a glass slide. In this system, while the photoluminescence (PL) of donor QDs immobilized on a surface was quenched due to the presence of AuNPs (energy acceptor) in close proximity, the protease activity caused modulation in the efficiency of the energy transfer between the acceptor and donor, thus enabling the protease assay. In comparison to the QD-dye system, the conjugate of the QD-AuNP gave rise to higher energy transfer efficiency, resulting in quantitative assay of proteases with more sensitivity. When matrix metalloproteinase, caspase, and thrombin were tested, a multiplexed assay was successfully achieved since the AuNP could be used as a common energy acceptor in conjunction with QDs having different colors. Our system is anticipated to find applications in the diagnosis of protease-related diseases and screening of potential drugs with high sensitivity in a high-throughput way.