Complete physicochemical characterization of DNA/chitosan complexes by multiple detection using asymmetrical flow field-flow fractionation

Asymmetrical flow field-flow fractionation (AF4) coupled with UV-vis spectrophotometry, multiangle light scattering (MALS), and dynamic light scattering (DLS) detection was used to analyze dispersions of DNA/rhodamine B labeled chitosan (Ch-rho) complexes frequently used as gene delivery vectors. The method yielded, in a single experiment, important characteristics of the complexes, such as their hydrodynamic radius, size distribution, conformation, composition, and the amount of free Ch-rho in the dispersions. Samples for analysis were obtained by varying experimental parameters known to influence the transfection efficiency of DNA/chitosan complexes, including the DNA concentration at mixing (82-164 μg/mL), the ratio of chitosan amino groups to DNA phosphate groups (3 ≤ N/P ratio ≤ 15), the chitosan molecular weight (10-76 kDa), and its degree of deacetylation. In all preparations, DNA/Ch-rho complexes had hydrodynamic radii ranging from 15 to 160 nm. Both the DNA concentration and the Ch-rho molecular weight influence the size distribution of the complexes: a greater fraction of large particles was detected in dispersions prepared with the most concentrated DNA solution or the Ch-rho of highest molar mass. All dispersions contained free Ch-rho in solution. The free Ch-rho content ranged from 53 to 92% of the total Ch-rho concentration in dispersions prepared with N/P ratios from 3 to 15, respectively, implying that the N/P ratio of the complexes ranged from 1.3 to 1.6 in all samples. The accuracy of the free Ch-rho determination by AF4/UV-vis/MALS+DLS was confirmed by an independent method involving (1) ultracentrifugation of the dispersions prepared with unlabeled chitosan and (2) analysis of the supernatant by the Orange II dye depletion method. This study demonstrates the ability of AF4/UV-vis/MALS+DLS to provide a complete physicochemical characterization of DNA/polycation complexes used in nonviral gene delivery.     

Comparative Nanoparticle Size Characterization of EEW Alumina Using Various Measurement Techniques

Modern material science is paying more attention on the development of nanomaterials for superior properties in various fields of applications like mechanical, thermal, electronic, bio-medical etc. For such applications, determination of nanoparticle sizes along with their distribution is important for attaining the desired properties. Particle sizes along with the crystallite sizes of oxides, non-oxides and metallic nanopowders produced by different processes can be determined by different techniques which includes x-ray diffraction/neutron diffraction (XRD/ND), transmission electron microscopy/field emission scanning electron microscopy (TEM/FESEM), Brunauer-Emmett-Teller (BET) surface area method, small angle neutron scattering (SNAS), dynamic light scattering (DLS), static light scattering (SLS), etc. For average nano-metric particle size determination, DLS is the most frequently used technique that gives a distribution that approximates the exact binomial distribution of large numbers of nanoparticulates with varying particle size under investigation (Gaussian distribution). However, the other techniques mainly give either localized distribution of the particles under observation or the distribution derived from type II isotherm. In this investigation, nano-alumina powder produced by the electrical explosion of wire technique (EEW) is used for comparative evaluation of particle size analysis by DLS measurement technique for nanoparticles vis-à-vis to other techniques like XRD (for crystallite size), FESEM, BET, and TEM. The superiority of the DLS technique has been discussed in details with respect to the unique features of its Gaussian distribution nature.     

Systematic study of bimodal suspensions of latex nanoparticles using dynamic light scattering

Determining the size of nanoparticles accurately, quickly and easily is becoming more and more important as the use of such particles increases. One of the common techniques for measuring the size of particles in suspension is dynamic light scattering (DLS). In principle, DLS is able to estimate the hydrodynamic particle diameter and its intensity-weighted distribution. However, the measured correlation function or power spectrum must be inverted to obtain this size distribution. The inversion is an ill-posed mathematical problem, and only under certain assumptions can the distribution be determined reliably. Suspensions containing bimodal (or multi-modal) particle size distributions are particularly challenging. This study reports on DLS measurements on a range of bimodal distributions of latex spheres with varying ratios of particle sizes. To determine the efficacy of different inversion techniques, the data has been analyzed both with the algorithms implemented in the DLS instrument’s proprietary analysis software and with other inversion routines based on simple analytical models of the particle size distribution. In addition, the results of the DLS analysis have been compared to scanning and transmission electron microscopy (SEM and TEM) measurements.     

Role of surfactants on the stability of nano-zinc oxide dispersions

Nowadays, stable colloidal dispersions with ultra-fine or nanosized particles are getting importance due to their higher activity. In this article, methods for the preparation of stable aqueous dispersions of zinc oxide (ZnO) were discussed. The quality of the dispersion was improved by capping with different types of surfactants say non-ionic, cationic, and anionic. Accordingly, Triton X 100, polyethylene glycol-6000 (both non-ionic), cetyltrimethylammonium bromide (cationic), and sodium dodecyl sulfate (anionic) were selected for the study. Effect of these surfactants on particle size of ZnO was followed through dynamic light scattering (DLS) studies and zeta potential measurements. Particle size analysis and zeta potential measurement indicated that ZnO dispersions stabilized with anionic surfactants (sodium dodecyl sulfate) showed better stability. Further, the effect of ultrasonication on particle size distribution was examined and optimized.     

动态光散射在颗粒检测中的应用

动态光散射是常用的一种用于检测颗粒粒径分布的方法。本文详细介绍了该技术在测量颗粒粒径、介电常数、传导率、旋转扩散系数、环境的影响以及结晶条件等方面的研究进展,并对该技术的发展及应用做出了进一步的讨论,提出了动态光散射方法存在的问题,以及克服动态光散射的背景噪声、提高光源质量以及建立更智能化的算法等研究方向。     

Inkjet printable polyaniline-gold dispersions

Inkjet printable polyaniline-gold (PANI-Au) hybrid dispersions were synthesised using gold salt as oxidant to simultaneously induce chemical oxidative polymerisation of aniline and reduction of HAuCl₄ in bulk aqueous solution. By varying the amount of HAuCl₄ used for the polymerisation, the size, morphology and population of the resulting gold particles embedded within the polymer were controllable. It was shown however, that the metallic gold particles contained within the resulting dispersions did not appear to affect the bulk conductivity of PANI, but rather that by varying the amount of HAuCl₄ used, both the quality and printability of the resulting PANI-Au dispersion could be affected. PANI-Au synthesised using a ratio of 1:0.25 aniline:HAuCl₄ was shown to be optimum as it resulted in dispersions with high polymer conjugation lengths and doping levels, as well as high conductivity and well-defined electrochemistry. This hybrid material was shown to be highly processable, and inkjet printing of this material was demonstrated on flexible substrate which resulted in high quality, printed films.     

Dynamic light-scattering study of self-assembly of diblock copolymers in supercritical carbon dioxide

A high-pressure dynamic light-scattering (DLS) technique has been utilized to study the behavior in solution of poly(1, 1-dihydroperfluorooctylacrylate) and poly(vinyl acetate) (PFOA-b-PVAC) in supercritical carbon dioxide. The hydrodynamic-radius distribution for each species, such as unimers, micelles, and large aggregates, were determined under both isobaric and isothermal conditions over a pressure range of 9-55.2 MPa, and a temperature range of 25-75 degrees C, respectively. The DLS results clearly showed both pressure-induced and temperature-induced dissolution and association behavior for the copolymer in supercritical carbon dioxide. Also presented are some preliminary experimental results for the micellar self-assembly of a fluorinated block copolymer, poly(2-tetrahydropyranyl methacrylate)-b-poly(1h, 1h-perfluorooctyl methacrylate) (THPMA-b-F7MA), in supercritical carbon dioxide by use of a new high-pressure cell that allows us to conduct simultaneous small-angle x-ray scattering and DLS measurements.     

Interaction of ubiquinone-10 with dipalmitoylphosphatidylcholine and their formation of small dispersed particles

Stable aqueous dispersions of ubiquinone-10 (UQ) were obtained by cosonication with dipalmitoylphosphatidylcholine (DPPC) in the UQ mole fraction range 0.1-0.7. To clarify the dispersal mechanism, the dispersed particles were characterized, and the interaction between UQ and DPPC was investigated using several physicochemical techniques. Dynamic light scattering (DLS) measurements showed that the diameter of the dispersed particles was 50-70 nm. A limited amount of UQ was incorporated into DPPC bilayer membranes (approximately 5 mol%). The trapped aqueous volume inside the particles was determined fluorometrically using the aqueous space marker calcein, and the volume in the UQ/DPPC particles decreased remarkably with the addition of UQ into small unilamellar vesicles of DPPC. The decline in the fraction of vesicular particles was also confirmed by fluorescence quenching of N-dansylhexadecylamine in the DPPC membrane by the addition of the quencher CuSO₄. These results indicate that the excess UQ separated from the DPPC bilayers is stabilized as emulsion particles by the DPPC surface monolayer.     

Colorimetric and dynamic light scattering detection of DNA sequences by using positively charged gold nanospheres: a comparative study with gold nanorods

We introduce a new genosensing approach employing CTAB (cetyltrimethylammonium bromide)-coated positively charged colloidal gold nanoparticles (GNPs) to detect target DNA sequences by using absorption spectroscopy and dynamic light scattering. The approach is compared with a previously reported method employing unmodified CTAB-coated gold nanorods (GNRs). Both approaches are based on the observation that whereas the addition of probe and target ssDNA to CTAB-coated particles results in particle aggregation, no aggregation is observed after addition of probe and nontarget DNA sequences. Our goal was to compare the feasibility and sensitivity of both methods. A 21-mer ssDNA from the human immunodeficiency virus type 1 HIV-1 U5 long terminal repeat (LTR) sequence and a 23-mer ssDNA from the Bacillus anthracis cryptic protein and protective antigen precursor (pagA) genes were used as ssDNA models. In the case of GNRs, unexpectedly, the colorimetric test failed with perfect cigar-like particles but could be performed with dumbbell and dog-bone rods. By contrast, our approach with cationic CTAB-coated GNPs is easy to implement and possesses excellent feasibility with retention of comparable sensitivity--a 0.1 nM concentration of target cDNA can be detected with the naked eye and 10 pM by dynamic light scattering (DLS) measurements. The specificity of our method is illustrated by successful DLS detection of one-three base mismatches in cDNA sequences for both DNA models. These results suggest that the cationic GNPs and DLS can be used for genosensing under optimal DNA hybridization conditions without any chemical modifications of the particle surface with ssDNA molecules and signal amplification. Finally, we discuss a more than two-three-order difference in the reported estimations of the detection sensitivity of colorimetric methods (0.1 to 10-100 pM) to show that the existing aggregation models are inconsistent with the detection limits of about 0.1-1 pM DNA and that other explanations should be developed.     

Transient behavior of granular materials as result of tumbler shape and orientation effects

Granular flows are most often investigated at steady-state conditions. This allows time-averaged analysis to display results such as velocity profiles and convective accelerations within the thin flowing layer. Typically in rotating tumblers, constant rotation rates and circular shapes are used as they jointly produce a steady, uniform flowing layer at the free surface. Conversely, unsteady flowing layers can be generated through any combination of varying the rotation rate of a tumbler or using a non-circular cross-sectional shape to change the length of the flowing layer. The unsteady conditions, however, require the additional complexity of ensemble-averaged analysis of images in a sequence of multiple trials. The experiments of this paper examine the properties of unsteady flow produced by triangular-shaped rotating tumblers at constant rotation rates. The geometric shape naturally causes periodic changes in the flowing layer as a function of the instantaneous orientation of the triangle. Multiple experiments were conducted in which the parameters of tumbler dimension, particle size, fill level and rotation rate were varied in all combinations. The free surface properties of angle of repose and flowing layer length, position, and curvature are reported. Results show that the arithmetic difference between the angle of repose and the tumbler orientation has a functional relationship with the instantaneous flowing layer length in the form of a catenary indicating a minimization of energy in the granular flow. Furthermore, the oscillation of the flowing layer position appears to affect the free surface curvature in the upstream regions. This is likely due to the rapidly increasing and decreasing length of the free surface limiting the space where particles can enter or exit the flowing layer. Ultimately, the unsteady macroscopic properties of the free surface flowing layer in the triangular tumblers provide some indication of the complexities of granular velocity and acceleration that contribute to the mixing and segregation in this unique tumbler shape.     

Synthesis and dispersion of yttria-stabilized zirconia (YSZ) nanoparticles in supercritical water

Yttria-stabilized zirconia (YSZ) nanoparticles were synthesized in supercritical water (SCW) without the use of mineralizers that are conventionally used to ensure basic conditions during synthesis. Process parameters were varied and their effect on the synthesis yield and particle morphology and composition were investigated. Conditions for synthesizing a stoichiometric YSZ nanopowder were identified. Dry YSZ particles collected in the continuous SCW process were redispersed in water in order to study their aggregation characteristics (including the size of agglomerates and the degree of agglomeration) in aqueous dispersions. Surface modification by the addition of polyethylenimine (PEI) was shown to result in stable dispersions of particles with average diameters between 50 nm and 100 nm.     

Digital holographic microscopy with reduced spatial coherence for three-dimensional particle flow analysis

We investigate the use of a digital holographic microscope working in partially coherent illumination to study in three dimensions a micrometer-size particle flow. The phenomenon under investigation rapidly varies in such a way that it is necessary to record, for every camera frame, the complete holographic information for further processing. For this purpose, we implement the Fourier-transform method for optical amplitude extraction. The suspension of particles is flowing in a split-flow lateral-transport thin separation cell that is usually used to separate the species by their sizes. Details of the optical implementation are provided. Examples of reconstructed images of different particle sizes are shown, and a particle-velocity measurement technique that is based on the blurred holographic image is exploited.     

Application of dynamic light scattering to the study of small marine particles

Small particles ranging from approximately 0.1 μm to several micrometers in size, which include detrital material, bacteria, and other planktonic microorganisms, make a significant contribution to light scattering in the upper ocean. The scattering properties of these particles are strongly dependent on their size, which is difficult to measure in the submicrometer range with commonly used electronic resistive counters and microscopic techniques. We examined the size of small marine particles by application of the dynamic light scattering (DLS) method. In this method the time-dependent autocorrelation function of scattered intensity by particles undergoing Brownian motion provides information about the size of particles. The samples were collected in clear oceanic waters off the coast of Southern California. The mean hydrodynamic diameter of particles, determined from the DLS measurements at a scattering angle of 45°, was 0.54μ m. This indicates that the major contribution to scattering at this angle comes rom submicrometer particles. We also described an inverse method for estimating the general slope of the size distribution of small marine particles from the mean hydrodynamic diameter. This method is based on calculations of the size distribution weighted by distribution from Mie theory and assumes that a power-law approximation represents the actual particle scattered intensity. These calculations suggested that particulate assemblage in our seawater samples was best characterized by a differential size distribution with a slope of -4.35. This estimation was supported by independent measurements of particle size distribution and the spectral beam attenuation coefficient taken from the same samples as those used for the DLS measurements. We also demonstrated that multiangle DLS measurements may be used to determine the representative value of the refractive index of particles.     

Inline method of droplet and particle size distribution analysis in dilute disperse systems

In the present article a measurement method of particle size distributions (PSD) in industrial installations which use a dispersed phase of low concentration (like spray dryers or spray scrubbers) is introduced. A new type of inline-measurement system has been developed and designed to work in spray drying conditions. A standard digital camera is used to record shadows of flowing particles inside the spray drying chamber. Collected images were analyzed by a newly developed software which recognizes particles only in the focus area and eliminates several types of artifacts. The constructed prototype of the PSD inline-analyzer was installed and used to monitor large laboratory scale spray dryer. All data collected by the designed system during the spray drying experiments were compared with data measured with an offline reference system to show accuracy of the new measurement technique.     

pH-independent dissolution enhancement for multiple poorly water-soluble drugs by nano-sized solid dispersions based on hydrophobic–hydrophilic conjugates

The objective of this study was to achieve an optimal formulation of hydrophilic–hydrophobic conjugates for nano-sized solid dispersions (SDs) with enhanced dissolution of multiple drugs in different gastrointestinal (GI) tract environments. A new conjugate powder with an optimized process was used to fabricate SDs that contained three poorly water-soluble drugs that were also poorly soluble in different dissolution media. The self-assembled nanoparticle formation, drug crystallinity and SD molecular interactions were investigated by measuring the particle size during dissolution testing and physicochemical property analysis (powder X-ray diffraction and Fourier transform infrared spectroscopy). Drug release studies indicated that SD containing conjugated powder significantly improved the dissolution rates of these poorly water-soluble drugs in the GI tract. In addition, particle size analysis showed nano-sized particles in the dissolution media in the early stage with a tendency to reduce smaller particles over time. Physicochemical characterizations demonstrated almost amorphous drug states and hydrogen bonding interactions between the drugs and conjugates in the SD. This study optimized a promising material for SD, and the material was shown to have a promising performance under various pH medium conditions with poorly water-soluble drugs.     

Modification of gellan gum films by halloysite: physicochemical evaluation and drug permeation properties

The aim of this study was to determine the potential of gellan gum (GG) and halloysite (HS) dispersions at different mixing ratios and to investigate the potential of GG-HS dispersions in film formation. To this end, the dispersions and films were characterized. The dispersions formed films with large particles ranging from 3 to 4?μm in size, with a zeta potential of ～?35?mV. The GG-HS films were fabricated using a solvent-casting technique, which generated films with a white opaque appearance and rough surface. The GG-HS films were formed via hydrogen bonding and electrostatic interactions at the inner cavity and outer surface, as confirmed by ATR-FTIR spectroscopy and X-ray diffractometry. The %water uptake and erosion of the GG-HS film decreased with increasing HS content, whereas both puncture strength and elongation were increased in the GG-HS ratios of 1:0.4 and 1:1.2. Moreover, addition of HS into the GG films could possibly decrease drug permeability coefficient when using higher HS ratio in acidic and neutral media. These results suggested that HS modifies the characteristics of the GG used to coat modified-release tablets.     

Labeling detonation nanodiamond suspensions using the optical methods

The percentage of large particles in the water suspension of diamond nanoparticles to a large extent determines the potential of using these suspensions in technology and medicine. It is demonstrated that there is an error in determining the percentage of large diamond nanoparticles in water suspensions using the dynamic light scattering (DLS) method to measure the size distribution of the particles. A method for labeling these suspensions based on supplementing the DLS measurements with recording of an optical spectrum in the visible region is proposed. The labeling allows one to perform more reliable determination of the percentage of large particles in a suspension.     

Gas thermodynamics and optics of a monodisperse supersonic jet interacting with an aerodynamic body

On the basis of the previously developed gas dynamics model of the polydisperse jet flowing over a blunt body, the optics of a compressed layer is studied under close-to-experimental conditions. The effect of scattering of monochromatic radiation by the particles on the observed picture in the ??laser sheet?? plane is numerically estimated. The study is carried out on the assumption that the cloud formed by the particles is optically thin (single scattering). The effects of absorption and scattering of the radiation by the carrying gas are neglected. The numerical studies have been carried out for wide ranges of the particle sizes and optical parameters of the matter.     

铁粒子多分散系统磁流变液的制备和性能研究

磁流变液是铁磁性颗粒分散到低粘度的油中形成的稳定的悬浊液。其扩散特性主要由颗粒本身的物性和颗粒间的相互作用而决定。为了更好的控制颗粒间的相互作用,我们加入同样物性,但尺寸更小的颗粒,以调控悬浊液的流动特性。研究显示,在高体积百分比的磁流变液中加入亚微米尺寸的铁颗粒可以显著改善流体在没有外加磁场情况下的流动特性。受范得华力影响,加入的小颗粒首先附着在大颗粒周围,形成组装体,组装体间范得华力较小,从而有效降低了流体粘度。流体的粘度随着小颗粒在大颗粒上附着的比例不同而变化。随着小颗粒的增加,流体中铁颗粒的体积百分比增加,从而提高了磁流变液在磁场中的屈服应力,增强了磁流变液的磁流变效果。