Effect of carrier ionic strength in microscale cyclical electrical field-flow fractionation

Recent work with cyclical electrical field-flow fractionation systems has shown promise for the technique as a separation and analysis tool, but little is understood about how the carrier composition in the system affects its capabilities. The electrical properties of microscale CyElFFF systems change when the carrier ionic conditions are altered, and it is well known that the effects of increasing ionic strength carriers on retention in normal ElFFF systems are severe. Specifically, retention levels fall significantly. Accordingly, this work seeks to understand the effect that increasing carrier ionic strength in CyElFFF has on nanoparticle retention in the channels. The retention of polystyrene particles in the CyElFFF microsystem is reported at various ionic strengths of ammonium carbonate and at a variety of pH levels. The experiments are compared to the theory of CyElFFF available in the literature. The results indicate that the ionic strength of the carrier has a significant impact on retention and that high ionic strength carrier solutions lead to poor performance of the CyElFFF system. These results have significant impact on the possible uses of the technique and its applications, especially in the biomedical arena.     

Miniaturized flow fractionation device assisted by a pulsed electric field for nanoparticle separation

Electric field flow fractionation (EFFF) is a powerful separation technique based on an electrical field perpendicular to a pressure-driven flow. Previous studies of microelectric field flow fractionation (micro-EFFF) indicate that separation performance was limited due to a weak effective electric field caused by polarization layers on the electrode surfaces. In this work, we report on a micro-EFFF device that uses a pulsed voltage scheme to overcome these limitations. The device was fabricated in indium tin oxide (ITO)-coated glass with ITO as electrodes. The effective electric field for pulsed voltage operation was found to be 50-fold stronger when compared with constant voltage operation. A strong influence of pulsed voltage frequency on nanoparticle retention times was observed. Using pulsed voltage, improved separation of polystyrene particles of different surface charge and particle size is demonstrated. Pulsed voltage also offers more parameters compared to the constant voltage mode, e.g., pulse frequency, duty cycle, and waveform to optimize the retention behavior of analytes.     

Capillary magnetic field flow fractionation and analysis of magnetic nanoparticles

This paper reports the purification and analysis of magnetic nanoparticles using capillary magnetic field flow fractionation, which utilizes an applied magnetic field oriented orthogonal to the capillary flow. To validate this approach as a separation method for nanometer-scale particles, samples of magnetic nanoparticles composed of either gamma-Fe2O3 (maghemite) or CoFe2O4 with average diameters ranging from 4 to 13 nm were prepared and characterized by transmission electron microscopy and SQUID magnetometry. Retention of the samples on the capillary was investigated as a function of solvent flow rate and the nanoparticle size and composition; the elution times of the nanoparticles are strongly dependent on their magnetic moments. We demonstrate the use of this method to separate a mixture of nanoparticles into size-monodisperse fractions. The magnetic moments of the particles are calculated based on analysis of the retention parameters and correlate with values obtained in separate SQUID magnetometry measurements.     

Steric-hyperlayer sedimentation field flow fractionation and flow cytometry analysis applied to the study of Saccharomyces cerevisiae

Sedimentation field flow fractionation separation associated with flow cytometry has been used for the characterization of several commercial Saccharomyces cerevisiae yeasts used for wine production. A new type of channel 80 microm thick and new operating conditions, such as sample introduction when field and flow are established and a channel inlet connected to the accumulation wall, were used. Good repeatability (5% RSD) and reduced analysis time (2-10 min) were obtained. The avoidance of the stop-flow relaxation process in conjunction with the use of a channel of reduced thickness has demonstrated that an effective "steric-hyperlayer" mode driving to a major focusing effect of the species in the channel thickness is involved in the elution of the yeast cells. Flow cytometry analyses were performed, and the forward scattering and side scattering yeast characteristics correlation maps were obtained. Field flow fractionation and flow cytometry information obtained indicated that the fractogram profiles of the yeast cell depended not only on the size, but also on the shape and density.     

Characterization of surface-modified nanoparticles for in vivo biointeraction. A sedimentation field flow fractionation study

Sedimentation field flow fractionation (SdFFF) is an emerging high-performance analytical tool for separation and determination of size and adsorption characteristics of colloidal particles. This study demonstrates how SdFFF can be used to characterize nanoparticles prepared for in vivo applications including (1) the quantification of polymer uptake on nanoparticles where surface coverage is crucial and (2) the coupling of cell adhesive peptides containing the Arg-Gly-Asp motif (RGD). Quantitative information about polymer adhesion in order to prepare a bioinert surface and an accurate determination of ligand uptake are both of obvious importance for the understanding of, for example, relations between the number of attached molecules for biointeraction and an observed therapeutic effect. In addition, the present work highlights the necessity to perform careful characterization of commercially available particulate starting materials, in terms of size and polydispersity, prior to biological experimentation.     

Electrical field-flow fractionation for metal nanoparticle characterization

The potential of electrical field-flow fractionation (ElFFF) for characterization of metal nanoparticles was investigated in this study. Parameters affecting separation and retention such as applied DC voltage and flow rate were examined. Nanoparticles with different types of stabilizers, including citrate and tannic acid, were investigated. Changes to the applied voltage showed a significant influence on separation in ElFFF, and varying flow rate was used to improve plate heights in the experiments. For nanoparticles of a fixed size, the separation was based primarily on electrophoretic mobility. Particles with low electrophoretic mobility elute earlier. Therefore, citrate stabilized gold nanoparticles (-2.72 × 10(-4) cm(2) V(-1) s(-1)) eluted earlier than tannic acid stabilized gold nanoparticles (-4.54 × 10(-4) cm(2) V(-1) s(-1)) of the same size. In addition, ElFFF can be used for characterization of gold nanoparticles with different particle sizes including 10, 20, and 40 nm with a fixed stabilizing agent. For a specific separation condition, the separation of 10, 20, and 40 nm gold nanoparticles was clearly based on the particle size as opposed to the electrophoretic mobility, as the elution order was in order of decreasing mobility for 10 (-4.54 × 10(-4) cm(2) V(-1) s(-1)), 20 (-3.97 × 10(-4) cm(2) V(-1) s(-1)), and 40 (-3.76 × 10(-4) cm(2) V(-1) s(-1)) nm particles, respectively.     

Circular asymmetrical flow field-flow fractionation for the semipreparative separation of particles

A new technique for the separation and characterization of particles and polymers based on asymmetrical flow field-flow fractionation was developed. The new circular asymmetrical flow field-flow fractionation instrument (CAFFFE) resembles a quasi-parallel arrangement of 12 individual flow channels. As compared to the classical asymmetrical flow field-flow fractionation (AF-FFF), which can be used so far only for analytical separation and characterization of particles and polymers, the CAFFFE allows the introduction of higher amounts of sample into the channel in a single run so that semipreparative to preparative separation becomes possible. This was demonstrated by the separation of polymer latex standards.     

Mechanistic investigation of nanoparticle motion in pulsed voltage miniaturized electrical field flow fractionation device by in situ fluorescence imaging

In our previous study, we reported a miniaturized electrical field flow fractionation device (micro-EFFF) that used a pulsed voltage (PV) to increase the effective electric field and, hence, improved the separation performance. In this work, we developed two micro-EFFFs with planar or segmented electrode design and investigated the particle movement in the flow channels under a PV. Numerical simulation was used to understand the electric field distribution in the micro-EFFFs. When the calculations for the micro-EFFF with a segmented electrode (segmented micro-EFFF) and the micro-EFFF with planar electrodes (planar micro-EFFF) are compared, a stronger electric field at the top electrode segments is found in the segmented micro-EFFF, with the strongest field at the edges of the electrode segments. Nanoparticle motion in both devices was in situ visualized by using a fluorescence microscope equipped with a CCD-camera. Results reveal that electrophoresis governs the nanoparticle movement in the planar micro-EFFF and dielectrophoresis dominates the movement in the segmented micro-EFFF. Two models are postulated to explain the experimental observations of the nanoparticle movement. The mechanistic understanding of controlling nanoparticle motion in a miniaturized environment will help the design and application of micro-EFFF for the separation of charged biomolecules (proteins and DNAs).     

Magnetohydrodynamic (MHD) flows of viscoelastic fluids in converging/diverging channels

The present work is a theoretical investigation of the applicability of magnetic fields for controlling hydrodynamic separation in Jeffrey-Hamel flows of viscoelastic fluids. To achieve this goal, a local similarity solution was found for laminar, two-dimensional flow of a viscoelastic fluid obeying second-order/second-grade model as its constitutive equation with the assumption being made that the flow is symmetric and purely radial. These assumptions enabled a third-order nonlinear ODE to be obtained as the single equation governing the MHD flow of this particular fluid in flow through converging/diverging channels. With three physical boundary conditions available, Chebyshev collocation-point method was used to solve this ODE numerically. Results are presented in terms of parameters such as Reynolds number, Weissenberg number, channel half-angle, and the magnetic number. It was found that these parameters all have a profound effect on the velocity profiles in Jeffrey-Hamel flows. The effect of magnetic field was found to be more striking in that it is predicted to force fluid elements near the wall to exceed centerline velocity in converging channels and to suppress separation in diverging channels. Interestingly, the effect of the magnetic field in delaying flow separation is predicted to become more pronounced the higher the fluid’s elasticity.     

Triboelectric separation of a starch-protein mixture – Impact of electric field strength and flow rate

Triboelectric separation is a method for separating dry particulate systems due to their different electrostatic chargeability. Previous applications are limited to the separation of coarse powders. The aim of the present study is to examine the influence of the flow conditions and the influence of the electric field strength on the separation efficiency of starch and protein particles. Very fine organic powders are separated in a simple bench scale electrostatic separator to extend this technique to powders below 50?µm. The influence of different gas flow rates in the turbulent flow regime on particle charging and subsequent separation is investigated.As an organic model substrate, a mixture of barley starch and whey protein was used. The tribocharger consists of a PTFE charging tube and a rectangular separation chamber where an electric field is applied between two electrodes. The particles are conveyed through the charging tube and charged by frictional contact with the tube wall. It is shown that different gas flow rates at a turbulent flow regime in the charging tube did not change the separation characteristics. In contrast, increasing electrical field strength increases separation efficiency of protein particles regardless of gas flow conditions. The proportion of starch at the anode is the same for all the investigated parameters.     

Asymmetrical flow field-flow fractionation and multiangle light scattering for analysis of gelatin nanoparticle drug carrier systems

The physicochemical properties of nanosized colloidal drug carrier systems are of great influence on drug efficacy. Consequently, a broad spectrum of analytical techniques is applied for comprehensive drug carrier characterization. It is the primary objective of this paper to present asymmetrical flow field-flow fractionation (AF4), coupled online with multiangle light scattering detection, for the characterization of gelatin nanoparticles. Size and size distribution of drug-loaded and unloaded nanoparticles were determined, and data were correlated with results of state-of-the-art methods, such as scanning electron microscopy and photon correlation spectroscopy. Moreover, the AF4 fractionation of gelatin nanoparticulate carriers from a protein model drug is demonstrated for the first time, proposing a feasible way to assess the amount of loaded drug in situ without sample preparation. This hypothesis was set into practice by monitoring the drug loading of nanoparticles with oligonucleotide payloads. In this realm, various fractions of gelatin bulk material were analyzed via AF4 and size-exclusion high-pressure liquid chromatography. Mass distributions and high-molecular-weight fraction ratios of the gelatin samples varied, depending on the separation method applied. In general, the AF4 method demonstrated the ability to comprehensively characterize polymeric gelatin bulk material as well as drug-loaded and unloaded nanoparticles in terms of size, size distribution, molecular weight, and loading efficiency.     

Working without accumulation membrane in flow field-flow fractionation

Nonideal interaction of sample with the separation device is a difficulty found in chromatographic methods as well as in field-flow fractionation. However, in field-flow fractionation (FFF), greater flexibility in the choice of carrier solution composition is possible, thus reducing the need of a wide choice of surface chemistry when nonideal sample interaction is to be minimized. The use of an ultrafiltration membrane as the surface for the accumulation wall is common practice in flow field-flow fractionation. Typical membranes in use are laminates of a skin membrane onto a backing material such as woven polyester. At this point, only a limited choice of membrane chemistries is available. Many membranes have been developed for protein applications as membranes are widely used in the pharmaceutical industries. While these membranes work well for protein applications, flow field-flow fractionation is applicable to polymeric particulate as well as protein samples. Thus, sample interaction with the membrane surface is possible with nonprotein applications and these interactions can induce significant secondary effects on retention ratio and affect instrumental reliability. Also, the woven texture of membranes may detrimentally affect the FFF separation. For these reasons, the study of flow field-flow fractionation using a flat, smooth surface of controlled chemistry is of relevance. We present here the results of a new, membraneless channel that uses a bare frit as the accumulation wall and that is intended for analysis of micrometer-sized particles only. Selectivity results are comparable to those obtained with the membrane, while relative sample recovery indicates that the best quantitative performance can be obtained without the membrane. Moreover, neither sample immobilization nor losses through the frit occur when operating membraneless. On the other hand, first experimental evidence of a certain level of frit surface activity suggests that optimization of experimental conditions is required.     

Equilibrium gradient methods with nonlinear field intensity gradient: a theoretical approach

Equilibrium gradient methods belong to a family of separation techniques in which analytes are forced to unique equilibrium points by a force gradient and a counter force along the separation pathway. The basic theory for equilibrium gradient methods where the force gradient is induced by a field gradient is developed in this paper. The results indicate that peak capacity can be dynamically improved by using a nonlinear field-intensity gradient in which the first section is steep, and the following section is shallow. Using electromobility focusing (EMF) as an example, a separation model is established. EMF is an equilibrium gradient method that uses an electric field intensity gradient to induce a force gradient on charged analytes, such as proteins, and a constant hydrodynamic flow as an opposing force. Equations relating operating parameters with separation performance are given. Although simulation results show that a peak capacity of over 10,000 is theoretically possible using a single channel in a separation time just under 2 months, if 100 parallel separation units are utilized in an array format under the same operating conditions, the same peak capacity can be obtained in just over 12 h.     

Pinched flow fractionation: continuous size separation of particles utilizing a laminar flow profile in a pinched microchannel

A concept of "pinched flow fractionation" for the continuous size separation and analysis of particles in microfabricated devices has been proposed and demonstrated. In this method, particles suspended in liquid were continuously introduced into a microchannel having a pinched segment and were aligned to one sidewall in the pinched segment by another liquid flow without particles. The particles were then separated perpendicularly to the flow direction according to their sizes by the spreading flow profile inside the microchannel. Polymer microbeads were successfully separated, and the effects of the flow rate and channel shapes on the separation performance were examined. Also, separated particles were collected independently by making branches at the end of the pinched segment. Since this method utilizes only the laminar flow profile inside a microchannel, complicated outer field control could be eliminated, which is usually required for other kinds of particle separation methods such as field flow fractionation. Also, this method can be applied both for particle size analysis and for preparation of monodispersed particles, since separation can be rapidly and continuously performed.     

Nonintrusive Monitoring of Slug Sequence and Flow Stability in Dense-Phase Pneumatic Conveying

This article presents three sensing methods developed for the nonintrusive monitoring of important flow parameters in dense-phase pneumatic conveying. With the optical measurement system, images of the flow are acquired and an image analysis is used to determine the sequence, length, and velocity of slugs for given materials and operating conditions. The conveying parameters of interest are also monitored with a capacitive sensor by means of exploiting electrical properties of the flowing media. The charge-based measurement system uses a field meter to determine the electric field strength caused by charged particles and provides information about the sequence and regularity of the moving slugs. The noninvasive principle of all three methods avoids concerns about particle contact effects (e.g., wear of the measurement equipment or interference with the flow). All three prototype sensors have been tested under slug flow conditions. A comparison of the three sensing methods against key requirements in pneumatic conveying reveals that capacitive sensing seems to be best suited for reliable flow determination in slug flow.     

Nonintrusive Monitoring of Slug Sequence and Flow Stability in Dense-Phase Pneumatic Conveying

This article presents three sensing methods developed for the nonintrusive monitoring of important flow parameters in dense-phase pneumatic conveying. With the optical measurement system, images of the flow are acquired and an image analysis is used to determine the sequence, length, and velocity of slugs for given materials and operating conditions. The conveying parameters of interest are also monitored with a capacitive sensor by means of exploiting electrical properties of the flowing media. The charge-based measurement system uses a field meter to determine the electric field strength caused by charged particles and provides information about the sequence and regularity of the moving slugs. The noninvasive principle of all three methods avoids concerns about particle contact effects (e.g., wear of the measurement equipment or interference with the flow). All three prototype sensors have been tested under slug flow conditions. A comparison of the three sensing methods against key requirements in pneumatic conveying reveals that capacitive sensing seems to be best suited for reliable flow determination in slug flow.     

Electric discharge control of flow separation on oblique airfoil

The possibility of controlling flow separation on an oblique airfoil using dielectric-barrier discharge has been experimentally studied. The experiments were performed at subsonic flow velocities in a broad range of the angle of attack. The results of measurements of the velocity and surface pressure fields and an analysis of the flow patterns show that the application of electric discharge allows the interval of the angles of attack for separation-free flow past the airfoil to be significantly increased. Various discharge regimes have been studied, including those with continuous activation by single voltage pulses with a frequency of 0.5–5 kHz and by pulse trains at a repetition rate of 1–100 Hz. The efficiency of the flow separation control has been studied as dependent on the electrical parameters, frequency characteristics, and position of the discharge relative to the flow separation line.     

Separation by nanoparticles plasmonic resonance with low stress in microfluidics channel (analytical and design)

In this study, nanoparticles near‐field plasmonic resonance is used to improve the traditional cell separation main outputs such as viability and efficiency. The live cells viability is severely depend on stresses, which are applied on cells in the microfluidics channel. Hence, for improving the cell viability, the enforced stresses inside of the structure should be declined. The major factors of the enforced stresses are related to the electric field non‐uniformity, which are attributed to the hurdles and applied voltage magnitude. Therefore, in this study, a new structure is presented and thereby, the magnitude of the applied stresses on live cells is minimised which is contributed to the decreasing the non‐uniformity strength of channel. It should be noted that in the new structure two arrays of nanoparticles were used to produce a short range and localised non‐uniform electrical field because of their near‐field plasmonic resonance. Hence, the enforced stress on the live cell severely decreased at the far‐field and confined at the small section of the channel. It is due to, the near‐field plasmonic amplitude is dramatically disappeared by increasing distance, hence, the cells far from the nanoparticles will be endured the low level but effective amount of the optical force.Inspec keywords: nanoparticles, nanomedicine, plasmonics, cellular biophysics, microfluidics, bioMEMS, electrophoresis, separationOther keywords: optical force, dielectrophoresis, short range localised nonuniform electrical field, cell viability, microfluidics channel, cell separation, near‐field plasmonic resonance, nanoparticles     

Mechanism for the separation of large molecules based on radial migration in capillary electrophoresis

We demonstrate a novel separation mechanism for large molecules based on their radial migration in capillary electrophoresis with applied hydrodynamic flow (HDF). The direction of radial migration depends on the direction of the applied HDF relative to the electric field. The radial migration velocities are size-dependent, which could be attributed to the different degree of deformation under shear flow. Analytical separation was demonstrated on a sample plug containing lambda DNA (48 502 bp) and phiX174 RF DNA (5386 bp) with baseline separation. Alternatively, this separation mode can be performed continuously and is thus applicable to preparative separations. Without the need for gel/polymer or complex instrumentation, this separation technique is complementary to capillary gel electrophoresis and field-flow fractionation. Although large DNA molecules were used to demonstrate the separation mechanism here, these protocols could also be applied to the separation of proteins, cells, or particles based on size, shape, or deformability.