A method to fabricate 2D nanoparticle arrays

This article demonstrates an efficient approach to fabricate nanoparticles arranged in a periodic pattern over a large area. A nanoscale gold film coated on a silicon wafer substrate was sectioned into grids by focused ion beam machining. Through a thermal treatment, the film in a confined area transforms into a nanoparticle due to the surface tension effect of the melted gold film. By controlling the film thickness and the size of the confined area, a nanoparticle array with various particle sizes and interparticle spacings can be manipulated. This approach may have great potential applications in sensor chips and nonlinear devices.     

Evaluating the Control Banding Nanotool: a qualitative risk assessment method for controlling nanoparticle exposures

Control banding (CB) strategies offer simplified processes for controlling worker exposures in the absence of firm toxicological and exposure information. The nanotechnology industry is an excellent candidate for applying such strategies with overwhelming uncertainties of work-related health risks posed by nanomaterials. A recent survey shows that a majority of nanomaterial producers are not performing a basic risk assessment of their product in use. The CB Nanotool, used internationally, was developed to conduct qualitative risk assessments to control nanoparticle exposures. Nanotoxicology experts have requested standardization of toxicological parameters to ensure better utility and consistency of research. Such standardization would fit well in the CB Nanotool’s severity and probability risk matrix, therefore enhancing the protection of nanotechnology industry workers. This article further evaluates the CB Nanotool for structure, weighting of risk factors, and utility for exposure mitigation, and suggests improvements for the CB Nanotool and the research needed to bolster its effectiveness.     

A novel method to prepare Au nanocage@SiO_2 nanoparticle

Gold （Au） nanocage@SiO2 nanoparticles are prepared by a novel approach. The silver （Ag） nanocube@SiO2 structure is synthetized firstly. Next, the method of etching a SiO2 shell by boiling water is adopted to change the penetration rate of AuCl4- through the SiO2 shell. AuCl4- can penetrate through silica shells of different thickness values to react with the Ag nanocube core by changing the incubation time. The surface plasma resonance （SPR） peak of synthetic Au nanocage@SiO2 can be easily tuned into the near-infrared region. Besides, CdTeS quantum dots （QDs） are successfully connected to the surface of Au nanocage@SiO2, which testifies that the incubation process does not change the property of silica.     

纳米磁粒子应用于非接触式温度测量的研究

借助纳米磁粒子,通过测量其在不同温度下一、三次谐波幅值,使用郎之万函数达到求解温度的目的。首先对郎之万函数进行Taylor展开,进行简单的化简,然后根据正弦磁场下一、三次谐波的求解方式,把郎之万函数代入其中,构建温度和一、三次谐波幅值的函数关系。在较弱磁场的作用下,进行了三组实验,分别在-5℃～0℃、-15℃～0℃以及-25℃～0℃上进行实验研究。通过与光纤温度计测试结果的对比,发现这种方法在-25℃～0℃这个温度区间内可以实现精确温度测量,其误差为0.02 K～0.2 K。     

Comparing different hard-thermal-loop approaches to quark number susceptibilities

We compare our previously proposed hard-thermal-loop (HTL) resummed calculation of quark number susceptibilities using a self-consistent two-loop approximation to the quark density with a recent calculation of the same quantity at the one-loop level in a variant of HTL-screened perturbation theory. Besides pointing out conceptual problems with the latter approach, we show that it severely over-includes the leading-order interaction effects, while including none of the plasmon terms, which is the main reason for requiring improved resummation schemes. Received: 27 June 2002 / Revised version: 23 September 2002 / Published online: 31 January 2003     

Efficient systemic DNA delivery to the tumor by self-assembled nanoparticle

There are few techniques to measure in situ the size distribution and density of fluidized nanoparticle agglomerates. Visualization techniques, which are the most applied approach, currently have two important limitations: (1) they do not allow a continuous determination of the terminal velocity of the agglomerates, because it is necessary to stop the fluidization and (2) often, the agglomerates are tracked in very dilute zones of the bed, typically in the splash zone, where agglomerates are likely not representatives for the agglomerates in the whole bed. In this communication, we propose a sampling technique that allows to determine the size distribution and terminal velocity of fluidized agglomerates larger than ～20 μm continuously, in situ, and allows to work with concentrations of agglomerates higher than other reported techniques.     

Characterisation of nanoparticle size and state prior to nanotoxicological studies

Before commencing any nanotoxicological study, it is imperative to know the state of the nanoparticles to be used and in particular their size and size distribution in the appropriate test media is particularly important. Particles satisfying standards can be commercially purchased; however, these invariably cannot be used directly and need to be dispersed into the relevant biological media. Often such changes in the environment or ionic strength, or a change in the particle concentration, results in some aggregation or a shift in the particle size distribution. Such unexpected aggregation, dissolution or plating out, if unaccounted for, can have a significant effect on the available nanoparticle dose and on interpretation of any results obtained thereafter. Here, we demonstrate the application of characterisation instrumentation that sizes nanoparticles based on their Brownian motion in suspension. Unlike classical light-scattering techniques, the nanoparticle tracking and analysis (NTA) technique allows nanoparticles to be sized in suspension on a particle-by-particle basis allowing higher resolution and therefore better understanding of aggregation than ensemble methods (such as dynamic light scattering (DLS) and differential centrifugation sedimentation (DCS)). Results will be presented from gold (standard) nanoparticles in biologically relevant media that emphasise the importance of characterisation of the nanoparticle dispersion. It will be shown how the NTA technique can be extended to multi-parameter analysis, allowing for characterization of particle size and light scattering intensity on an individual basis. This multi-parameter measurement capability allows sub-populations of nanoparticles with varying characteristics to be resolved in a complex mixture. Changes in one or more of such properties can be followed both in real time and in situ.     

How to measure chi(3) of a nanoparticle

Most of the known methods to measure the nonlinear optical properties of materials deal with the bulk properties, but there are many demanding applications that require those measurements to be done on a single particle or a single molecule. We report a novel application of nonlinear optics to measure the third-order nonlinear optical susceptibility of nanoparticles in solutions. By measuring the power of the third harmonic generated in a diluted solution of nanoparticles, both the size and chi(3) can be extracted from a simple set of measurements.     

Direct imaging of nanoparticle embedding to probe viscoelasticity of polymer surfaces

Atomic force microscopy was used to study the embedding of gold nanoparticles into the surface of polystyrene films. The rate of embedding was determined at temperatures near the bulk glass transition temperature T(g) by measuring the apparent nanosphere height as a function of annealing time. In particular, relative height measurements of the adhered particles were made at temperatures below the bulk T(g) value. In the absence of enhanced surface dynamics or yield processes no embedding is expected to occur for T相似文献   

Plasmonic nanoparticle monomers and dimers: from nanoantennas to chiral metamaterials

We review the basic physics behind light interaction with plasmonic nanoparticles. The theoretical foundations of light scattering on one metallic particle (a plasmonic monomer) and two interacting particles (a plasmonic dimer) are systematically investigated. Expressions for the effective particle susceptibility (polarizability) are derived, and applications of these results to plasmonic nanoantennas are outlined. In the long-wavelength limit, the effective macroscopic parameters of an array of plasmonic dimers are calculated. These parameters are attributable to an effective medium corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial where plasmonic monomers or dimers have the function of “meta-atoms”. It is shown that planar dimers consisting of rod-like particles generally possess elliptical dichroism and function as atoms for planar chiral metamaterials. The fabricational simplicity of the proposed rod-dimer geometry can be used in the design of more cost-effective chiral metamaterials in the optical domain.     

Silver and gold nanoparticle coated membranes applied to protein dot blots

Detection and identification of low abundance biomarker proteins is frequently based on various types of membrane-based devices. Lowering of the protein detection limits is vital in commercial applications such as lateral flow assays and in Western blots widely used in proteomics. These currently suffer from insufficient detection sensitivity and low retention for small 2–5 kDa proteins. In this study, we report the deposition of two types of metal nanoparticles: gold colloids (50–95 nm diameter) and silver fractals onto a range of commonly used types of membranes including polyvinylidene fluoride (PVDF). Due to strong affinity of proteins to noble metals, such modified membranes have the potential to effectively capture trace proteins preventing their loss. The membranes modified by metal particles were characterized optically and by SEM. The membrane performance in protein dot blots was evaluated using the protein—fluorophore conjugates Deep Purple-bovine serum albumin and fluorescein—human serum albumin. We found that the metal nanoparticles increase light extinction by metals, which is balanced by increased fluorescence, so that the effective fluorescence signal is unchanged. This feature combined with the capture of proteins by the nanoparticles embedded in the membrane increases the detection limit of membrane assays.     

Scaling of transverse nuclear magnetic relaxation due to magnetic nanoparticle aggregation

The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles decreases the transverse nuclear magnetic resonance (NMR) relaxation time of adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse-echo sequence. This effect is commonly used to measure the concentrations of a variety of small molecules. We perform extensive Monte Carlo simulations of water diffusing around SPIO nanoparticle aggregates to determine the relationship between and details of the aggregate. We find that in the motional averaging regime scales as a power law with the number N of nanoparticles in an aggregate. The specific scaling is dependent on the fractal dimension d of the aggregates. We find for aggregates with d=2.2, a value typical of diffusion limited aggregation. We also find that in two-nanoparticle systems, is strongly dependent on the orientation of the two nanoparticles relative to the external magnetic field, which implies that it may be possible to sense the orientation of a two-nanoparticle aggregate. To optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is best to have aggregates with few nanoparticles, close together, measured with long pulse-echo times.     

Observation of superparamagnetism to flux closure behaviour in ZnO nanoparticle agglomerates

In this paper we have tried to understand the nature of magnetism in ZnO nanoparticle samples with an intrinsic 50?ppm trace of Fe impurity. When the samples are annealed we observe formation of nanoparticle agglomerates and the size increases with annealing temperature. When the sample is annealed at 600?°C we observe superparamagnetic behaviour, and the magnetic hysteresis along with the coercive field below the blocking temperature is almost independent of the cooling field. When the sample is annealed at 900?°C we observe reduction of saturation magnetization but the magnetic hysteresis and the coercive field are now dependent on the cooling field, indicating magnetic correlation and ordering within the agglomerated nanograins. We propose a simple model that explains the reduction of magnetization as being due to a vortex-state-like flux closure formation.     

实验物理创造教学与传统教学的比较

对实验物理创造教学与实验物理传统教学进行了比较,以求有助于从根本上理解和把握实验物理创造教学的实质。     

Application of Lanczos-based time-dependent density-functional theory approach to semiconductor nanoparticle quantum dots

We present a density-functional theory study of Si nanoparticle quantum dots, focusing on determination of their optical properties. To calculate the absorption spectra of our quantum dot models we use a recently-developed method based on the application of Lanczos algorithms to linear-response time-dependent density-functional theory (LR-TDDFT). Quantum dot models are obtained by cutting Si atoms from the bulk crystal lattice and adding appropriate H terminating atoms to the surface; these structures are relaxed using density-functional theory in the plane-wave pseudopotential supercell approach, and then absorption spectra are calculated. We verify that with increasing size of the nanoparticle, the optical gap/onset of absorption steadily moves to lower energies. The paper represents an important demonstration of this new methodology on a class of systems that are the focus of significant current research in nanoscience.     

Structure and switching of single-stranded DNA tethered to a charged nanoparticle surface

Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA(ss DNA)tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows: i) when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii)for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii) when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.     

A Simple method to prepare multi-walled carbon nanotube/ZnO nanoparticle composites

A multi-wall carbon nanotube (MWCNT)/ZnO nanoparticle composite is fabricated by the thermal decomposition of a mixture of Zn(NH₃)₄CO₃, MWCNTs and polyvinyl pyrrolidone (PVP). From the infrared spectra of dried samples of Zn(NH₃)₄CO₃, PVP, and the mixture of Zn(NH₃)₄CO₃ and PVP, we show that there is a coordination interaction between the Zn of Zn(NH₃)₄CO₃ and the carbonyl of PVP. Thermal decomposition of the mixture of Zn(NH₃)₄CO₃ and PVP with MWCNTs results in the decomposition of Zn(NH₃)₄CO₃ to ZnO nanoparticles which are well-dispersed on the outer walls of the MWCNTs. The results show that PVP can be used to control the ZnO nanoparticle size and its dispersion on the MWCNTs walls during decomposition. This method is favorable for large scale synthesis. PACS 61.10.Nz; 61.46.Fg; 61.46.Df; 78.30.-j     

Optical pulling force on nanoparticle clusters with gain due to Fano-like resonance

We demonstrate that, in a simple linearly-polarized plane wave, the optical pulling forces on nanoparticle clusters with gain can be induced by the Fano-like resonance. The numerical results based on the full-wave calculation show that the optical pulling forces can be attributed to the recoil forces for the nanoparticle clusters composed of dipolar nanoparticles with three different configurations. Interestingly, the recoil forces giving rise to optical pulling forces are exactly dominated by the coupling term between the electric and magnetic dipoles excited in the nanoparticle clusters, while other higher-order terms have a negligible contribution. In addition, the optical pulling force can be tailored by modulating the Fano-like resonance via either the particle size or the gain magnitude, offering an alternative freedom degree for optical manipulations of particle clusters.     

The transition from spark to arc discharge and its implications with respect to nanoparticle production

Indium (III) phthalocyanine (InPc) was encapsulated into nanoparticles of PEGylated poly(d,l-lactide-co-glycolide) (PLGA-PEG) to improve the photobiological activity of the photosensitizer. The efficacy of nanoparticles loaded with InPc and their cellular uptake was investigated with MCF-7 breast tumor cells, and compared with the free InPc. The influence of photosensitizer (PS) concentration (1.8–7.5 μmol/L), incubation time (1–2 h), and laser power (10–100 mW) were studied on the photodynamic effect caused by the encapsulated and the free InPc. Nanoparticles with a size distribution ranging from 61 to 243 nm and with InPc entrapment efficiency of 72 ± 6 % were used in the experiments. Only the photodynamic effect of encapsulated InPc was dependent on PS concentration and laser power. The InPc-loaded nanoparticles were more efficient in reducing MCF-7 cell viability than the free PS. For a light dose of 7.5 J/cm² and laser power of 100 mW, the effectiveness of encapsulated InPc to reduce the viability was 34 ± 3 % while for free InPc was 60 ± 7 %. Confocal microscopy showed that InPc-loaded nanoparticles, as well as free InPc, were found throughout the cytosol. However, the nanoparticle aggregates and the aggregates of free PS were found in the cell periphery and outside of the cell. The nanoparticles aggregates were generated due to the particles concentration used in the experiment because of the small loading of the InPc while the low solubility of InPc caused the formation of aggregates of free PS in the culture medium. The participation of singlet oxygen in the photocytotoxic effect of InPc-loaded nanoparticles was corroborated by electron paramagnetic resonance experiments, and the encapsulation of photosensitizers reduced the photobleaching of InPc.