十字星形金属纳米粒子的消光性质

单纳米粒子的LSPR光学生物传感器具有空间分辨率高, 可植入生物的细胞和组织里, 检测所需要的剂量少等优势。本文提出一种十字星形的纳米粒子结构以进一步提高单纳米粒子LSPR光学生物传感器的信号强度。模拟和分析表明, 十字星形纳米粒子的消光效率远远高于相同结构尺寸的菱形或三角形纳米粒子的消光效率, 为发展新型结构单或阵列式的金属纳米粒子LSPR光学生物传感器提供了参考依据。     

Size Determination of Au Aerosol Nanoparticles by Off-Line TEM/STEM Observations

Determination of particle size distributions of Au aerosol nanoparticles has been performed by a TEM/STEM investigation. The particles are generated by an evaporation/condensation method and are size-selected by differential mobility analyzers (DMA) based on their electrical mobility. Off-line TEM measurements resulted in equivalent projected area diameters assuming that the particles are spherical in shape. In this paper critical factors such as magnification calibration, sampling, image analysis, beam exposure and, particle shape are treated. The study shows that the measures of central tendency; mean, median and mode, are equal as expected from a narrow size distribution. Moreover, the correlation between TEM/STEM and DMA are good, in practice 1:1. Also, STEM has the advantage over TEM due to enhanced contrast and is proposed as an alternative route for determination of particle size distributions of nanoparticles with lower contrast.     

Size Tunable Fabrication of Magnetic Alginate Microparticles Using Flow Focusing Microfluidics

The size tunable formulation of magnetic alginate microparticles (MAMs) using a 3D flow-focusing microfluidic device is reported. The droplet phase consists of iron oxide nanoparticles (IONPs) in an alginate solution and the continuous phase consists of fluorocarbon oils. The stability of IONP colloids in alginate and calcium ethylenediamine tetraacetic acid solutions using optical microscopy, dynamic light scattering, and zeta potential measurements is studied. These studies suggest that IONPs coated with polyethylene glycol (PEG) are most stable. MAMs using the PEG-coated IONP colloid are then formulated and it is studied how MAM the average size and coefficient of variance vary as a function of droplet and continuous phase flow rates and viscosities. Droplet and MAM size decrease when the carrier flow rate or viscosity increases, and droplet and MAM size increase when droplet flow rate or viscosity increases. Crosslinking and drying of droplets result in MAMs whose diameter is ≈44% less than the original droplets while maintaining a population coefficient of variance below 8%. Conditions are identified that enable fabrication of MAMs with diameters between 30 and 60 µm with coefficients of variance of ≈6–7%. These results may guide future work exploring the role of MAM size on various applications.     

In Situ Charge Characterization of TiO<Subscript>2</Subscript> and Cu–TiO<Subscript>2</Subscript> Nanoparticles in a Flame Aerosol Reactor

Charge distribution characteristics were investigated for nanoparticles synthesized in a diffusion flame aerosol reactor. The nanoparticles considered were pristine TiO₂ and Cu–TiO₂, with Cu dopant concentrations ranging from 1 to 5 wt% with particle size from 25 to 60 nm. In situ measurements were conducted by integrating a tandem differential mobility analyzer (TDMA) experimental setup with the flame aerosol reactor. A charging model was used to identify the important parameters that govern the two charging mechanisms (diffusion and thermo-ionization) in the flame and their relative importance at different operating parameters. The results indicate that TiO₂ and Cu–TiO₂ nanoparticles carry single as well as double unit charges. The charged fraction depends on particle size as well as on dopant concentration. The charged fraction increased with increasing particle size and decreased with copper dopant concentration. Measured charged fractions were similar for both the polarities at different mobility diameters. Based on the flame operating parameters, the calculations indicate that diffusion charging is dominant in the flame, which is consistent with the experimental results.     

Comparison of nanoparticle measurement instruments for occupational health applications

Nanoparticles are used in many applications because of their novel properties compared to bulk material. A growing number of employees are working with nanomaterials and their exposure to nanoparticles trough inhalation must be evaluated and monitored continuously. However, there is an ongoing debate in the scientific literature about what are the relevant parameters to measure to evaluate exposure to level. In this study, three types of nanoparticles (ammonium sulphate, synthesised TiO₂ agglomerates and aerosolised TiO₂ powder, modes in a range of 30–140 nm mobility size) were measured with commonly used aerosol measurement instruments: scanning and fast mobility particle sizers (SMPS, FMPS), electrical low pressure impactor (ELPI), condensation particle counter (CPC) together with nanoparticle surface area monitor (NSAM) to achieve information about the interrelations of the outputs of the instruments. In addition, the ease of use of these instruments was evaluated. Differences between the results of different instruments can mainly be attributed to the nature of test particles. For spherical ammonium sulphate nanoparticles, the data from the instruments were in good agreement while larger differences were observed for particles with more complex morphology, the TiO₂ agglomerates and powder. For instance, the FMPS showed a smaller particle size, a higher number concentration and a narrower size distribution compared with the SMPS for TiO₂ particles. Thus, the type of the nanoparticle was observed to influence the data obtained from these different instruments. Therefore, care and expertise are essential when interpreting results from aerosol measurement instruments to estimate nanoparticle concentrations and properties.     

Models of nanoparticles movement,collision, and friction in chemical mechanical polishing (CMP)

Nanoparticles have been widely used in polishing slurry such as chemical mechanical polishing (CMP) process. The movement of nanoparticles in polishing slurry and the interaction between nanoparticles and solid surface are very important to obtain an atomic smooth surface in CMP process. Polishing slurry contains abrasive nanoparticles (with the size range of about 10–100 nm) and chemical reagents. Abrasive nanoparticles and hydrodynamic pressure are considered to cause the polishing effect. Nanoparticles behavior in the slurry with power-law viscosity shows great effect on the wafer surface in polishing process. CMP is now a standard process of integrated circuit manufacturing at nanoscale. Various models can dynamically predict the evolution of surface topography for any time point during CMP. To research, using a combination of individual nanoscale friction measurements for CMP of SiO₂, in an analytical model, to sum these effects, and the results scale CMP experiments, can guide the research and validate the model. CMP endpoint measurements, such as those from motor current traces, enable verification of model predictions, relating to friction and wear in CMP and surface topography evolution for different types of CMP processes and patterned chips. In this article, we explore models of the microscopic frictional force based on the surface topography and present both experimental and theoretical studies on the movement of nanoparticles in polishing slurry and collision between nanoparticles, as well as between the particles and solid surfaces in time of process CMP. Experimental results have proved that the nanoparticle size and slurry properties have great effects on the polishing results. The effects of the nanoparticle size and the slurry film thickness are also discussed.     

金纳米棒的飞秒激光组装研究

金属纳米粒子对于研究表面等离子体共振具有非常重要的意义,其自组装形成的功能组装体能够展现出更加优异的整体协同性能.本文通过飞秒激光加工对金纳米棒直接进行组装,不引入其它的修饰剂,过程简单、快速(约1 min),不仅保留了金纳米棒表面等离子特性,且可以实现金纳米棒的任意精细图案化.将组装的微纳结构用于微流控芯片表面增强拉曼散射探测,可以得到很好的增强效果,为等离子体器件的制备提供了新的方法.     

Femtosecond laser microstructuring: an enabling tool for optofluidic lab‐on‐chips

This paper provides an overview of the rather new field concerning the applications of femtosecond laser microstructuring of glass to optofluidics. Femtosecond lasers have recently emerged as a powerful microfabrication tool due to their unique characteristics. On the one hand, they enable to induce a permanent refractive index increase, in a micrometer‐sized volume of the material, allowing single‐step, three‐dimensional fabrication of optical waveguides. On the other hand, femtosecond‐laser irradiation of fused silica followed by chemical etching enables the manufacturing of directly buried microfluidic channels. This opens the intriguing possibility of using a single laser system for the fabrication and three‐dimensional integration of optofluidic devices. This paper will review the state of the art of femtosecond laser fabrication of optical waveguides and microfluidic channels, as well as their integration for high sensitivity detection of biomolecules and for cell manipulation.     

Blue-shifted plasmon resonance of individual size-selected gold nanoparticles

The future implementation of integrated photonic devices requires the creation of nanostructures with well defined morphological and optical properties. To this end, we deposited size-selected gold nanoparticles produced by a gas phase aggregation cluster source on transparent substrates at room temperature with controlled impact energy. Interferometric optical detection measurements using a supercontinuum laser source demonstrated a blue-shifted plasmon resonance at the single particle level. The blue shift was observed to be more pronounced for small single clusters down to 3 nm in size.     

Fabrication and electrical characterization of a MOS memory device containing self-assembled metallic nanoparticles

Floating gate devices with nanoparticles embedded in dielectrics have recently attracted much attention due to the fact that these devices operate as non-volatile memories with high speed, high density and low power consumption. In this paper, memory devices containing gold (Au) nanoparticles have been fabricated using e-gun evaporation. The Au nanoparticles are deposited on a very thin SiO₂ layer and are then fully covered by a HfO₂ layer. The HfO₂ is a high-k dielectric and gives good scalability to the fabricated devices. We studied the effect of the deposition parameters to the size and the shape of the Au nanoparticles using capacitance–voltage and conductance–voltage measurements, we demonstrated that the fabricated device can indeed operate as a low-voltage memory device.     

Reversible multi polyelectrolyte layers on gold nanoparticles

The fabrication of semiconducting functional layers using low-temperature processes is of high interest for flexible printable electronics applications. Here, the one-step deposition of semiconducting nanoparticles from the gas phase for an active layer within a thin-film transistor is described. Layers of semiconducting nanoparticles with a particle size between 10 and 25?nm were prepared by the use of a simple aerosol deposition system, excluding potentially unwanted technological procedures like substrate heating or the use of solvents. The nanoparticles were deposited directly onto standard thin-film transistor test devices, using thermally grown silicon oxide as gate dielectric. Proof-of-principle experiments were done deploying two different wide-band gap semiconducting oxides, tin oxide, SnO _x , and indium oxide, In₂O₃. The tin oxide spots prepared from the gas phase were too conducting to be used as channel material in thin-film transistors, most probably due to a high concentration of oxygen defects. Using indium oxide nanoparticles, thin-film transistor devices with significant field effect were obtained. Even though the electron mobility of the investigated devices was only in the range of 10^?6?cm^2?V^?1?s^?1, the operability of this method for the fabrication of transistors was demonstrated. With respect to the possibilities to control the particle size and layer morphology in situ during deposition, improvements are expected.     

Mode-switching: A new technique for electronically varying the agglomeration position in an acoustic particle manipulator

Acoustic radiation forces offer a means of manipulating particles within a fluid. Much interest in recent years has focussed on the use of radiation forces in microfluidic (or “lab on a chip”) devices. Such devices are well matched to the use of ultrasonic standing waves in which the resonant dimensions of the chamber are smaller than the ultrasonic wavelength in use. However, such devices have typically been limited to moving particles to one or two predetermined planes, whose positions are determined by acoustic pressure nodes/anti-nodes set up in the ultrasonic standing wave. In most cases devices have been designed to move particles to either the centre or (more recently) the side of a flow channel using ultrasonic frequencies that produce a half or quarter wavelength over the channel, respectively.It is demonstrated here that by rapidly switching back and forth between half and quarter wavelength frequencies - mode-switching - a new agglomeration position is established that permits beads to be brought to any arbitrary point between the half and quarter-wave nodes. This new agglomeration position is effectively a position of stable equilibrium. This has many potential applications, particularly in cell sorting and manipulation. It should also enable precise control of agglomeration position to be maintained regardless of manufacturing tolerances, temperature variations, fluid medium characteristics and particle concentration.     

Agglomeration,isolation and dissolution of commercially manufactured silver nanoparticles in aqueous environments

The increasing use of manufactured nanoparticles ensures these materials will make their way into the environment. Silver nanoparticles in particular, due to use in a wide range of applications, have the potential to get into water systems, e.g., drinking water systems, ground water systems, estuaries, and/or lakes. One important question is what is the chemical and physical state of these nanoparticles in water? Are they present as isolated particles, agglomerates or dissolved ions, as this will dictate their fate and transport. Furthermore, does the chemical and physical state of the nanoparticles change as a function of size or differ from micron-sized particles of similar composition? In this study, an electrospray atomizer coupled to a scanning mobility particle sizer (ES-SMPS) is used to investigate the state of silver nanoparticles in water and aqueous nitric acid environments. Over the range of pH values investigated, 0.5–6.5, silver nanoparticles with a bimodal primary particle size distribution with the most intense peak at 5.0 ± 7.4 nm, as determined from transmission electron microscopy (TEM), show distinct size distributions indicating agglomeration between pH 6.5 and 3 and isolated nanoparticles at pH values from 2.5 to 1. At the lowest pH investigated, pH 0.5, there are no peaks detected by the SMPS, indicating complete nanoparticle dissolution. Further analysis of the solution shows dissolved Ag ions at a pH of 0.5. Interestingly, silver nanoparticle dissolution shows size dependent behavior as larger, micron-sized silver particles show no dissolution at this pH. Environmental implications of these results are discussed.     

Surface plasmons for enhanced silicon light-emitting diodes and solar cells

Localized surface plasmons on metallic nanoparticles can be surprisingly efficient at coupling light into or out of a silicon waveguide. In this paper we review our recent work where we have demonstrated a factor of 8 times enhancement in the electroluminescence from a silicon-on-insulator light-emitting diode at 900 nm using silver nanoparticles, in the first report of a surface plasmon-enhanced silicon light-emitting diode. Our theoretical work has shown that the enhancement seen in this system at long wavelengths is mainly a single-particle effect, in contrast to previous suggestions that it is a waveguide-mediated multi-particle effect, and that there is a dramatic enhancement of the scattering cross-section for waveguided light in these devices. We discuss the route towards increasing this enhancement further and provide predictions of the limits on the maximum potential efficiency enhancement, as well as the potential of metal particles for applications in thin film silicon solar cells.     

Fabrication of microelectrodes using flow layer-by-layer self assembly of gold nanoparticles

Microelectrodes to be used in microfluidic devices were prepared from the layer-by-layer flow deposition of gold nanoparticles. Pre-designed microfluidic channels were used as templates for the flow driven deposition of the nanoparticles in sequence with poly (diallyldimethyl amonium chloride) (PDADMAC). The electrical resistivity of the gold nanoparticle assembly was found to be strongly dependant on the concentration of sodium citrate used in the gold nanoparticle synthesis. As the electrical properties of the film changed from insulating to conducting when decreasing the citrate concentration, a 4 point probe setup was used to measure the resistivity of the film. Near bulk conductivity (5.42 × 10⁻⁶ Ω cm) was achieved with only 10 layers of film. The thickness and morphology of the flow-printed multilayer microelectrode was characterized using atomic force microscopy (AFM) and a field emission scanning electron microscope (FE-SEM). To demonstrate its usefulness, the microelectrode assembly was then tested toward the detection of KCl in solution, having a concentration ranging from 1 to 20 mM using AC current detection in a simple setup. Good linearity and stability of the electrode confirmed that this method could be very convenient for the fabrication of microelectrodes for lab-on-chip applications.     

Synthesis of mixed metallic nanoparticles by spark discharge

Short spark discharges (2 μs) were successfully applied to generate mixed particles a few nanometres in diameter by fast quenching. Alloyed Cr–Co electrodes were applied to demonstrate this. Further it was shown that if the anode and the cathode are different materials, the discharge process mixes the vapour of both materials, forming mixed nanoparticles. Electron microscopy (TEM, SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses were performed on the collected particles to study their size, morphology, composition and structure. The average compositions of the particles were measured by inductively coupled plasma (ICP). In addition, online measurements of the particle size distribution by mobility analysis were carried out. In the case of alloyed electrodes (Cr–Co), the relative concentration of the elements in the nanoparticulate sample was consistent with the electrode composition. When using electrodes of different metals (Au–Pd and Ag–Pd) the individual nanoparticles showed a range of mixing ratios. No surface segregation was observed in these mixed noble metal particles. Crystalline nanoparticulate mixed phases were found in all cases.     

Modelling for the robust design of layered resonators for ultrasonic particle manipulation

Several approaches have been described for the manipulation of particles within an ultrasonic field. Of those based on standing waves, devices in which the critical dimension of the resonant chamber is less than a wavelength are particularly well suited to microfluidic, or "lab on a chip" applications. These might include pre-processing or fractionation of samples prior to analysis, formation of monolayers for cell interaction studies, or the enhancement of biosensor detection capability. The small size of microfluidic resonators typically places tight tolerances on the positioning of the acoustic node, and such systems are required to have high transduction efficiencies, for reasons of power availability and temperature stability. Further, the expense of many microfabrication methods precludes an iterative experimental approach to their development. Hence, the ability to design sub-wavelength resonators that are efficient, robust and have the appropriate acoustic energy distribution is extremely important. This paper discusses one-dimensional modelling used in the design of ultrasonic resonators for particle manipulation and gives example of their uses to predict and explain resonator behaviour. Particular difficulties in designing quarter wave systems are highlighted, and modelling is used to explain observed trends and predict performance of such resonators, including their performance with different coupling layer materials.     

微流控制备单分散微米级SiO2微球

采用软模板法制备出了聚二甲基硅氧烷微流控装置。利用该装置讨论了正硅酸乙酯和氨水的用量分别对反应体系凝胶化时间的影响,确定了制备SiO2微球的优化反应体系,即二甲基乙酰胺、正硅酸乙酯和氨水的体积比为8∶4∶1,实验所需的反应温度为60 ℃。实验发现:在微流体通道中,分散相的流速越大,粒径越大;连续相流速越大,粒径越小。因此,通过控制微流控装置中分散相和连续相的流速制备了粒径40~220 m的单分散SiO2微球,并对其形貌进行表征。光学显微镜和粒径分析均表明所制备的SiO2微球球形度高,单分散性好。     

Crystal structure mediates mode of cell death in TiO2 nanotoxicity

Certain properties that nanoparticles possess differentiate them from their bulk counterparts, and these characteristics must be evaluated prior to nanoparticle studies and include: size, shape, dispersion, physical and chemical properties, surface area, and surface chemistry. Early nanotoxicity studies evaluating TiO₂ have yielded conflicting data which identify either size or crystal structure as the mediating property for nano-TiO₂ toxicity. However, it is important to note that none of these studies examined size with the crystal structure composition controlled for or examined crystal structure while controlling the nanoparticle size. The goal of this study was to evaluate the role of size and crystal structure in TiO₂ nanotoxicity while controlling for as many other nanoproperties as possible using the HEL-30 mouse keratinocyte cell line as a model for dermal exposure. In the size-dependent studies, all the nanoparticles are 100% anatase, and aggregate sizes were determined in order to take into account the effect of agglomeration on size-dependent toxicity. In addition, varying crystal structures were assessed while the size of the nanoparticles was controlled. We were able to identify that both size and crystal structure contribute to cytotoxicity and that the mechanism of cell death varies based on crystal structure. The 100% anatase TiO₂ nanoparticles, regardless of size, induced cell necrosis, while the rutile TiO₂ nanoparticles initiated apoptosis through formation of reactive oxygen species (ROS).     

Ensemble method to measure the potential energy of nanoparticles in an optical trap

A method is described for measuring the potential energy of nanoparticles in an optical trap by trapping an ensemble of particles with a focused laser beam. The force balance between repulsive osmotic and confining gradient-force pressures determines the single-particle trapping potential independent of interactions between the particles. The ensemble nature of the measurement permits evaluation of single-particle trapping energies much smaller than k_BT. Energies obtained by this method are compared to those of single-particle methods as well as to theoretical calculations based on classical electromagnetic optics.