Properties Of Single Particles Research Articles

Quantitative 3D Tracing of Gene-delivery Viral Vectors in Human Cells and Animal Tissues

Trafficking through a variety of cellular structures and organelles is essential for the interaction between gene-delivery vectors (i.e., adeno-associated virus (AAV) and liposomes) and host cells/tissues. Here, we present a method of computer-assisted quantitative 3D biodistribution microscopy that samples the whole population of fluorescently-labeled vectors and document their trafficking routes. Using AAV as a working model, we first experimentally defined numerical parameters for the singularity of Cy5-labeled particles by combining confocal microscopy and atomic force microscopy (AFM). We then developed a robust approach that integrates single-particle fluorescence imaging with 3D deconvolution and isosurface rendering to quantitate viral distribution and trafficking in human cells as well as animal tissues at the single-particle level. Using this quantitative method, we uncovered an as yet uncharacterized rate-limiting step during viral cell entry, while delineating nuclear accumulation of virions during the first 8 hours postinfection. Further, our studies revealed for the first time that following intramuscular injection, AAV spread progressively across muscle tissues through endomysium between myofibers instead of traversing through target cells. Such 3D resolution and quantitative dissection of vector-host interactions at the subcellular level should significantly improve our ability to resolve trafficking mechanisms of gene-delivery particles and facilitate the development of enhanced viral vectors.

Using laser light to trap and explore the cloud‐forming properties of single aerosol particles

Using laser light to trap and explore the cloud‐forming properties of single aerosol particles

Normal state of the copper oxide high-temperature superconductors

Superconductivity in the copper oxide ceramics stands as a grand challenge problem as its solution is fundamentally rooted in the physics of strong coupling. In such problems, traditional calculational schemes based on the properties of single particles fail. Rather, the physics of strong coupling

Photon mapping of individual Ag particles on MgO/Mo(001)

The optical properties of single Ag particles on an MgO thin film have been investigated with fluorescence spectroscopy performed in a scanning-tunneling-microscope setup. Depending on the point of excitation within the particle (top or side facet), two emission maxima are detected that are compatible with the in-plane and out-of-plane plasmons of the Ag deposits. The different excitation cross sections and spectral properties of the two modes give rise to characteristic intensity patterns in photon maps taken from individual particles.

Nanomechanical characterization of single micron‐sized polymer particles

AbstractThe mechanical characterization of single micron‐sized polymer particles is very important for understanding the anisotropic conductive adhesives interconnection. In this article, a nanoindentation‐based flat punch method was employed to investigate the mechanical properties of single polymer particles. A diamond flat tip, instead of a commonly used sharp tip for indentation, was specially designed to deform single polymer particles. The maximum applied load is 10 mN and the linear loading/unloading rate is 2 mN/s. Two types of amorphous polymer particles were examined. The polymer particles display significantly different stress–strain behaviors. The material responses at different strain levels were analyzed and compared. A particle size effect, the smaller the diameter, the harder the particle, on the compression stress–strain behavior, was observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Mechanical properties of individual microgel particles through the deswelling transition

Microgels are important materials for both basic science and engineering and have wide applications from the study of phase transitions to the delivery of drugs. These micron and sub-micron particles, made of hydrogel materials, respond to solvent conditions. The most common microgels are environmentally sensitive, responding to temperature and pH. Our material of interest, poly(N-isopropylacrylamide) or NIPAM, undergoes a deswelling transition above a critical temperature. The deswelling behavior of this polymeric material has been thoroughly studied in ensemble microgel systems as well as in bulk hydrogel samples. We present measurements of the elastic properties of single microgel particles through the deswelling transition using atomic force microscopy. While the fully collapsed particle (E = 123 kPa) is ten times stiffer than a fully swollen one (E = 13 kPa), we observe a dramatic softening of the particle near the transition (E = 3 kPa).

Digital signal processing methods for impedance microfluidic cytometry

Impedance microfluidic cytometry is a non-invasive, label-free technology that can characterize the dielectric properties of single particles (beads/cells) at high speed. In this paper we show how digital signal processing methods are applied to the impedance signals for noise removal and signal recovery in an impedance microfluidic cytometry. Two methods are used; correlation to identify typical signals from a particle and for a noisier environment, an adaptive filter is used to remove noise. The benefits of adaptive filtering are demonstrated quantitatively from the correlation coefficient and signal-to-noise ratio. Finally, the adaptive filtering method is compared to the Savitzky–Golay filtering method.

Optical properties of single mixed-phase aerosol particles

We examine the light scattering from wet aerosol particles whose core morphology is a random Gaussian sphere coated by different amounts of water. We compare the results with those calculated from a concentric-sphere particle and from a homogeneous-sphere particle whose refractive index is determined from the Bruggeman mixing rule. In nearly all cases the differences between those of the Gaussian-core and the concentric-sphere particles are small. The most significant differences are seen in calculations of the asymmetry parameters and the intensity and polarization phase functions. The results of the homogeneous-sphere particles vary significantly from those of the Gaussian-core particles, typically an order of magnitude greater than for the concentric-sphere particles. It is not uncommon to see differences of 10% in the efficiencies of large, homogeneous-sphere particles; whereas, in the intensity and polarization phase functions, differences of several tens of percent are not uncommon.

Single and bulk compression of pharmaceutical excipients: Evaluation of mechanical properties

The compaction of powders into tablets is widely used in the pharmaceutical industry to convert drugs, in the form of small particles, into coherent and robust metered solid dosage forms. In order to produce robust tablets with the required properties, it is essential to understand the elastic, viscoelastic and plastic properties and rupture strength of the feed particles, which can be as small as a few microns in diameter. The objective of this work is to characterise the mechanical properties of single particles using a micromanipulation diametrical compression technique and relate the parameters to the compression behaviour of powders. Mechanical parameters, such as the Young's modulus, hardness and nominal rupture stress, were thus determined for each sample. The bulk compression data of the powders were analysed to calculate the parameters of the Heckel (Heckel, R.W., 1961a An analysis of powder compaction phenomena, Trans Metal Soc. AIME, 221, 1001–1008; Heckel, R.W., 1961b Density–pressure relationships in powder compaction, Trans Metal Soc. AIME 671–675), Kawakita (Kawakita, K. and Ludde, K.H., 1971 Some considerations on powder compression equations, Powder Technology, 4, 61–68) and Adams (Adams, M.J., Mullier, M.A. and Seville, J.P.K., 1994 Agglomerate strength measurement using a uniaxial confined compression test, Powder Technology, 78, 5–13.) models. These parameters will be compared with each other, and with the mechanical properties of the individual component particles. A correlation has been found between the nominal rupture stress of single particles and the apparent strength derived from the Kawakita and Adams models.

Dielectrophoretic investigation of plant virus particles: Cow Pea Mosaic Virus and Tobacco Mosaic Virus

This paper reports experimental results on the dielectrophoretic (DEP) behaviour on two nonenveloped plant viruses of different geometrical shapes, namely Cow Pea Mosaic Virus (CPMV) and Tobacco Mosaic Virus (TMV). The DEP properties of carboxy-modified latex beads of the same size are also reported. The DEP properties of single particles were obtained from measurement of the frequency at which the DEP force on a particle goes to zero (the crossover frequency). The DEP behaviour of particle ensembles was also measured using image processing. The dielectric properties of the particles were evaluated from the DEP data. The surface conductance was found to be 0.3 nS for CPMV, 0.38 nS for TMV, and 0.52 nS for 27 nm diameter carboxy-latex beads. Data analysis has shown that the optimal condition for separation of TMV and CPMV is a low-conductivity suspending medium - below 1 mS/m.

TEM Study of PM2.5 Emitted from Coal and Tire Combustion in a Thermal Power Station

The research presented here was conducted within the scope of an experiment investigating technical feasibility and environmental impacts of tire combustion in a coal-fired power station. Previous work has shown that combustion of a coal+tire blend rather than pure coal increased bulk emissions of various elements (e.g., Zn, As, Sb, Pb). The aim of this study is to characterize the chemical and structural properties of emitted single particles with dimensions <2.5 microm (PM2.5). This transmission electron microscope (TEM)-based study revealed that, in addition to phases typical of coal fly ash (e.g., aluminum-silicate glass, mullite), the emitted PM2.5 contains amorphous selenium particles and three types of crystalline metal sulfates never reported before from stack emissions. Anglesite, PbSO4, is ubiquitous in the PM2.5 derived from both fuels and contains nearly all Pb present in the PM. Gunningite, ZnSO4-H2O, is the main host for Zn and only occurs in the PM derived from the coal+tire blend, whereas yavapaiite, KFe3+(SO4)2, is present only when pure coal was combusted. We conclude that these metal sulfates precipitated from the flue gas, may be globally abundant aerosols, and have, through hydration or dissolution, a major environmental and health impact.

Understanding the mechanical properties of single micro-particles and their compaction behaviour

The compaction of particulate materials to form tablets is increasingly employed as a final dosage form for functional products due to its simplicity and low cost. However, the functionality of some products may be impaired due to the high compression pressures required. The general aim of the current study is to understand the relationship between the mechanical properties of single feed particles (< 100 μm) and their compaction behaviour in order to produce tablets at low compression pressure with acceptable strength. The materials studied were pharmaceutical excipients, comprising three enteric polymer particles and three different powders in the form of agglomerates. The mechanical properties of the individual particles or agglomerates were determined by a micromanipulation technique. The samples were also compacted in cylindrical tableting dies. It was observed that there was a strong correlation between the forces required to cause the fracture of the single particles and those derived from the compaction measurements as determined using an existing analysis.

Characterization of the mechanical properties of polymeric chromatographic particles by micromanipulation

Chromatographic particles should not possess only desirable surface chemical properties but also mechanical properties. The latter determine the deformation of the particles under hydrodynamic conditions of packed beds and further the pressure drop. Understanding the mechanical properties of chromatographic particles is essential to successful design and operation of such processing equipment. The mechanical properties of single chromatographic particles made of different formulations and with different surface modifications were characterized by a novel micromanipulation technique. The principle of this technique is to compress single particles between two parallel surfaces. The force being imposed on the particles and their deformation under compression are measured simultaneously. The particles range from 30 to 300 μm, depending on their formulation. 10–30 particles from each sample were compressed up to a particle deformation of 70% in order to get statistically representative data. Particles for hydrophobic interaction chromatography were proved more stable than resins for ion exchange or gel filtration. The difference is remarkable in dry state and is less in wet state. Water seems to “level out” the differences in mechanical stability of resins. The stability seems to be also dependent on the speed of water release out of the resins.

Characterization of high heating-rate chars from alternative fuels using an electrodynamic balance

Important advantages in the use of alternative and renewable fuels (CO 2 reduction in the atmosphere, recovery of energy from wastes, limited SO x , NO x and heavy metal emissions) can be obtained only by solving technological and economical problems that make direct combustion of such fuels impractical. This is possible after a detailed investigation to determine the most important features of these materials in all steps of the thermal process. At present, few data can actually be found for the char properties of these fuels. Nevertheless, the knowledge of properties of chars (especially after severe devolatilization) is crucial for both modeling purposes (reactivity, kinetics of combustion and gasification, morphology variations, composition, and fate of pollutant precursors) and practical applications (boiler efficiency, ash deposition, and condensation causing fouling and slagging problems). This work deals with the characterization of chars from different classes of materials (biomasses, waste, and low and high volatile matter (VM) coals) obtained after a devolatilization performed in severe thermal conditions, i.e., high temperature and high heating rate. A methodological approach is developed, applied, and discussed, using an electrodynamic balance that is a versatile analyzer for the study of properties of single levitated particles. The specific heat, size, and shape distribution, and density variation between the char and the parent material are evaluated for all materials. Scanning electron microscopy (SEM) analysis is also carried out to investigate morphological variations and support the major results obtained with the electrodynamic analyzer.

Characterisation and magnetic behaviour of nickel nanoparticles encapsulated in carbon

In the previous papers, we reported the synthesis of nickel nanocrystals encapsulated in an amorphous carbon matrix by a method that consists in the sonochemical decomposition of the Ni(COD) 2 organometalic precursor followed by a heating treatment in vacuum. Both as-prepared and heated samples have been further characterised in the present paper by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) to determine the microstructure and the stability of the nickel nanocrystals for long periods of air storage. It has been shown that carbon is protecting the nickel nanocrystals from oxidation leading to a magnetic behaviour of the sample congruent with the superparamagnetic properties of single domain particles. The analysis of the frequency-dependent ac susceptibility leads to two well-defined distributions of particle size consistent with those observed in TEM experiments. The effective anisotropy constant has been determined for the two particle sizes of nickel nanoparticles.

On the structure of charge stabilized polymer dispersions

The present paper is concerned with the structure of dispersions made from charged polymer particles. First, the determination of important properties of single particles is discussed. It follows a typical phase diagram of charge stabilized dispersions. Their structure and possibilities to manipulate the structure are considered in the following sections. For the understanding of scattering experiments, as light scattering (LS), small angle neutron (SANS) and small angle synchrotron x-ray scattering (SAXS) the reciprocal lattice is of fundamental importance. A separate chapter, therefore, is dedicated to it. The application of shear has been found to be a particularly successful method for manipulating the structure of dispersions. It is possible to generate one-dimensional (1D) strings as well as plane (2D) layers which become (3D) crystals with time. The phenomena and structures generated by shear are in part surprising and at present not fully understood.

Optical Properties of Single Micron-Sized ZnO Particles Embedded in Alkali Halide Crystals Studied by Cathodoluminescence

In order to investigate optical properties of single micron-sized ZnO particles embedded in alkali halide (KCl) crystal, cathodoluminescence (CL) measurements at liquid helium temperature have been performed. In contrast to the case for pellet of ZnO powder, CL spectra of the single ZnO particles exhibit intense ultraviolet (UV) luminescence and no green emission due to oxygen vacancies, which ensures higher quality of the ZnO particles in the KCl crystal compared with that of the ZnO powder. The CL images of the single particles reveal several bright spots. The results indicate that radiative recombination of the excitons effectively occurs at specific areas in the surface of the single particle.

Optical Properties of Single Micron-Sized ZnO Particles Embedded in Alkali Halide Crystals Studied by Cathodoluminescence

In order to investigate optical properties of single micron-sized ZnO particles embedded in alkali halide (KCl) crystal, cathodoluminescence (CL) measurements at liquid helium temperature have been performed. In contrast to the case for pellet of ZnO powder, CL spectra of the single ZnO particles exhibit intense ultraviolet (UV) luminescence and no green emission due to oxygen vacancies, which ensures higher quality of the ZnO particles in the KCl crystal compared with that of the ZnO powder. The CL images of the single particles reveal several bright spots. The results indicate that radiative recombination of the excitons effectively occurs at specific areas in the surface of the single particle.

Homogeneity, Transport, and Signal Properties of Single Ag Particles Studied by Single-Molecule Surface-Enhanced Resonance Raman Scattering

We extended the sensitivity of Raman correlation spectroscopy in solution to the single-molecule level by applying surface- and resonance-enhanced Raman scattering (SERRS) combined with time-gated, confocal signal detection. The brightness of the SERRS signal of single Rhodamine 6G molecules adsorbed on a single silver nanoparticle is comparable to fluorescence. Rare event analysis reveals the existence of few particles with simultaneous SERRS and fluorescence signal. The observation of a dynamic exchange between heterogeneous binding sites is supported by the existence of multiple SERRS brightnesses in the signal intensity distribution and by signal fluctuations in the 60 μs time range detected by autocorrelation analysis. Finally, polarization-dependent SERRS autocorrelation curves and single-particle analysis allowed us to measure individual rotational diffusion times and to directly analyze the heterogeneity of the ensemble in solution.

Multiple scattering from rutile TiO2 particles

The physical properties of rutile titania (TiO2) have led to its wide use as a white pigment in many applications. The success of these applications depends not only on the optical properties of the bulk material, but also on subtle aspects of the scattering of light from collections of small TiO2 particles embedded in a transparent medium. We consider here the problem of multiple scattering in dense systems containing particles of a size comparable to the wavelength. Our method of analysis allowed us to understand the effects that the number density of particles and the particle size distribution have on the measured diffuse reflectance of such films. We apply this analysis to films of TiO2 particles in a transparent medium. We present the results of diffuse reflectance and transmittance measurements in the visible range of films with concentrations that span the range in which the radiation fields of adjacent particles begin to interact. We find that for λ<400 nm the spectra are predominantly determined by the scattering properties of the individual single particles. At longer wavelengths, where multiple-scattering effects become important, the particles behave as independent scatterers for volume concentrations of less than approximately 1%. At higher concentrations, where the interparticle spacing becomes less than the wavelength of light in the medium, the interaction of the radiation fields of adjacent particles lowers the backscattering fraction of the multiple-scattering function. This reduction in backscattering is significant for many of the applications of films containing TiO2, such as coatings and paper, which rely upon multiple scattering from large numbers of particles to provide the desired opacity.