Fractionation of Nanoparticle Matter in Red Wines Using Asymmetrical Flow Field-Flow Fractionation

The particle matter of wine is mainly composed of wine colloids and macromolecules. The present work develops a methodology using asymmetrical flow field-flow fractionation coupled with multi-angle light scattering, differential refractive index detector, and ultraviolet detector (AsFlFFF-MALS-dRI-UV) for the fractionation and determination of the molar mass, the hydrodynamic radius, and the apparent densities of the aggregates and macromolecules present in wine samples. The results from a set of six Argentinian high-altitude wines showed two main populations: the first population composed of wine colloids with higher UV-specific absorptivity and the second population composed of polysaccharides, such as arabinogalactans. The conformation results showed that population 1 consists of small and dense particles, while population 2 showed high molar masses and lower densities. The results demonstrated the use of AsFlFFF as a new, effective method for the fractionation and characterization of wine colloids and wine macromolecules in red wines with further potential applications.

A bifurcated continuous field-flow fractionation (BCFFF) chip for high-yield and high-throughput nucleic acid extraction and purification

We report a bifurcated continuous field-flow fractionation (BCFFF) chip for high-yield and high-throughput (20 min) extraction of nucleic acids from physiological samples. The design uses a membrane ionic transistor to sustain low-ionic strength in a localized region at a junction, such that the resulting high field can selectively isolate high-charge density nucleic acids from the main flow channel and insert them into a standardized buffer in a side channel that bifurcates from the junction. The high local electric field and the bifurcated field-flow design facilitate concentration reduction of both divalent cation (Ca2+) and molecular PCR inhibitors by more than two orders of magnitude, even with high-throughput continuous loading. The unique design with a large (>20 mM mm-1) on-chip ionic-strength gradient allows miniaturization into a high-throughput field-flow fractionation chip that can be integrated with upstream lysing and downstream PCR/sensor modules for various nucleic acid detection/quantification applications. A concentration-independent 85% yield for extraction and an overall post-PCR yield exceeding 60% are demonstrated for a 111 bp dsDNA in 10 μL of human plasma, compared to no amplification with the raw sample. A net yield four times larger than a commercial extraction kit is demonstrated for miR-39 in human plasma.

Recovery, overloading, and protein interactions in asymmetrical flow field-flow fractionation

In asymmetrical flow field-flow fractionation (AF4), similar to other separation techniques, mass recovery and overloading require special attention in order to obtain quantitative results. We conducted a systematic study with five globular proteins of different molecular weight (36.7–669 kDa) and isoelectric point (4.0–6.5), and ultrafiltration membranes that are commonly used in aqueous AF4, regenerated cellulose (RC) and polyethersulfone (PES). Phosphate-buffered saline (PBS) with ionic strength 0.15 M and pH 7.2 was used as the carrier liquid in this study. The actual molecular weight cutoff (MWCO) was found to be higher than the nominal value and varied between membranes of different chemistry but the same nominal MWCO. Adsorption on the membrane was found to be dependent on the membrane chemistry (RC had lower adsorption compared to PES), and independent of the protein standard for the examined proteins. On the other hand, the mass overloading effects (i.e., higher retention times, peak broadening, and fronting peaks) were significantly more pronounced for γ-globulin than for the other proteins. The overloading effects could be rationalized with the increase of the local viscosity close to the membrane, depending on the properties of the proteins, and we derived theoretical equations that related the dependency of the migration velocity on the protein concentration through this non-ideal viscosity effect.

A radial calibration window for analytical ultracentrifugation

Analytical ultracentrifugation (AUC) is a first-principles based method for studying macromolecules and particles in solution by monitoring the evolution of their radial concentration distribution as a function of time in the presence of a high centrifugal field. In sedimentation velocity experiments, hydrodynamic properties relating to size, shape, density, and solvation of particles can be measured, at a high hydrodynamic resolution, on polydisperse samples. In a recent multilaboratory benchmark study including data from commercial analytical ultracentrifuges in 67 laboratories, the calibration accuracy of the radial dimension was found to be one of the dominant factors limiting the accuracy of AUC. In the present work, we develop an artifact consisting of an accurately calibrated reflective pattern lithographically deposited onto an AUC window. It serves as a reticle when scanned in AUC control experiments for absolute calibration of radial magnification. After analysis of the pitch between landmarks in scans using different optical systems, we estimate that the residual uncertainty in radial magnification after external calibration with the radial scale artifact is ≈0.2 %, of similar magnitude to other important contributions after external calibration such as the uncertainty in temperature and time. The previous multilaboratory study had found many instruments with errors in radial measurements of 1 % to 2 %, and a few instruments with errors in excess of 15 %, meaning that the use of the artifact developed here could reduce errors by 5-to 10-fold or more. Adoption of external radial calibration is thus an important factor for assuring accuracy in studies related to molecular hydrodynamics and particle size measurements by AUC.

Detection of nanoplastics in food by asymmetric flow field-flow fractionation coupled to multi-angle light scattering: possibilities, challenges and analytical limitations

We tested the suitability of asymmetric flow field-flow fractionation (AF4) coupled to multi-angle light scattering (MALS) for detection of nanoplastics in fish. A homogenized fish sample was spiked with 100 nm polystyrene nanoparticles (PSNPs) (1.3 mg/g fish). Two sample preparation strategies were tested: acid digestion and enzymatic digestion with proteinase K. Both procedures were found suitable for degradation of the organic matrix. However, acid digestion resulted in large PSNPs aggregates/agglomerates (> 1 μm). The presence of large particulates was not observed after enzymatic digestion, and consequently it was chosen as a sample preparation method. The results demonstrated that it was possible to use AF4 for separating the PSNPs from the digested fish and to determine their size by MALS. The PSNPs could be easily detected by following their light scattering (LS) signal with a limit of detection of 52 μg/g fish. The AF4-MALS method could also be exploited for another type of nanoplastics in solution, namely polyethylene (PE). However, it was not possible to detect the PE particles in fish, due to the presence of an elevated LS background. Our results demonstrate that an analytical method developed for a certain type of nanoplastics may not be directly applicable to other types of nanoplastics and may require further adjustment. This work describes for the first time the detection of nanoplastics in a food matrix by AF4-MALS. Despite the current limitations, this is a promising methodology for detecting nanoplastics in food and in experimental studies (e.g., toxicity tests, uptake studies). Graphical abstract Basic concept for the detection of nanoplastics in fish by asymmetric flow field-flow fractionation coupled to multi-angle light scattering.

Characterization of charged polymer self-assemblies by multidetector thermal field-flow fractionation in aqueous mobile phases

Charged block copolymer self-assemblies, such as charged micelles, have attracted much attention as versatile drug delivery systems due to their readily tunable characteristics such as size and surface charge. However, current column-based analytical techniques are not suitable to fractionate and comprehensively characterize charged micelles in terms of size, molar mass, chemical composition and morphology. Multidetector thermal field-flow fractionation (ThFFF) is shown to be a unique characterization platform that can be used to characterize charged micelles in terms of size, molar mass, chemical composition and morphology in aqueous mobile phases with various ionic strengths and pH. This is demonstrated by the characterization of poly(methacrylic acid)-b-poly(methyl methacrylate) self-assemblies in high pH buffers as well as the characterization of cationic poly(2-vinyl pyridine)-b-polystyrene and poly(4-vinyl pyridine)-b-polystyrene self-assemblies in low pH buffers. Moreover, it is shown that ThFFF is capable of separating charged micelles according to the corona composition. These investigations prove convincingly that ThFFF is broadly applicable to the comprehensive characterization of amphiphilic self-assemblies even when aqueous mobile phases are used.

Localized Electroporation With Dielectrophoretic Field Flow Fractionation: Toward Removal of Circulating Tumour Cells From Human Blood

This paper presents the design and experimental performance of a microelectrode-based device to selectively lyse cells in a flow in a microfluidic channel. Localized cell lysis is achieved by utilizing "irreversible electroporation," in which cells are exposed to high magnitude electric pulses. Localized cell lysis in a flow has research applications and may allow for the removal of harmful cells, such as circulating tumor cells from blood. Due to the dependence of this technique on the magnitude of the applied electric field, lethal electric field regions can be localized in the channel by the calibration of the applied voltage. Dielectrophoresis field flow fractionation is used to levitate target cancer cells in the lethal region of the device microchannel. Experiments are performed to demonstrate the localized lysis of MCF7 cancer cells in a mixture of blood cells. Due to their larger size, these circulating tumor cell analogues levitate to a greater height in the channel than erythrocytes. MCF7 lysis is observed to increase from 4.6% in control experiments to 57.3% in active experiments. Leukocyte viability was unaffected in active experiments. These results demonstrate the feasibility of localizing cell lysis in a microfluidic flow environment.

Application of a novel sorting system for equine mesenchymal stem cells (MSCs)

The objective of this study was to validate non-equilibrium gravitational field-flow fractionation (GrFFF), an immunotag-less method of sorting mesenchymal stem cells (MSCs) into subpopulations, for use with MSCs derived from equine muscle tissue, periosteal tissue, bone marrow, and adipose tissue. Cells were collected from 6 young, adult horses, postmortem. Cells were isolated from left semitendinosus muscle tissue, periosteal tissue from the distomedial aspect of the right tibia, bone marrow aspirates from the fourth and fifth sternebrae, and left supragluteal subcutaneous adipose tissue. Aliquots of 800 × 10(3) MSCs from each tissue source were separated and injected into a ribbon-like capillary device by continuous flow (GrFFF proprietary system). Cells were sorted into 6 fractions and absorbencies [optical density (OD)] were read. Six fractions from each of the 6 aliquots were then combined to provide pooled fractions that had adequate cell numbers to seed at equal concentrations into assays. Equine muscle tissue-derived, periosteal tissue-derived, bone marrow-derived, and adipose tissue-derived mesenchymal stem cells were consistently sorted into 6 fractions that remained viable for use in further assays. Fraction 1 had more cuboidal morphology in culture when compared to the other fractions. Statistical analysis of the fraction absorbencies (OD) revealed a P-value of < 0.05 when fractions 2 and 3 were compared to fractions 1, 4, 5, and 6. It was concluded that non-equilibrium GrFFF is a valid method for sorting equine muscle tissue-derived, periosteal tissue-derived, bone marrow-derived, and adipose tissue-derived mesenchymal stem cells into subpopulations that remain viable, thus securing its potential for use in equine stem cell applications and veterinary medicine.

A tag-less method for direct isolation of human umbilical vein endothelial cells by gravitational field-flow fractionation

The analysis of cellular and molecular profiles represents a powerful tool in many biomedical applications to identify the mechanisms underlying the pathological changes. The improvement of cellular starting material and the maintenance of the physiological status in the sample preparation are very useful. Human umbilical vein endothelial cells (HUVEC) are a model for prediction of endothelial dysfunction. HUVEC are enzymatically removed from the umbilical vein by collagenase. This method provides obtaining a good sample yield. However, the obtained cells are often contaminated with blood cells and fibroblasts. Methods based on negative selection by in vitro passages or on the use of defined marker are currently employed to isolate target cells. However, these approaches cannot reproduce physiological status and they require expensive instrumentation. Here we proposed a new method for an easy, tag-less and direct isolation of HUVEC from raw umbilical cord sample based on the gravitational field-flow fractionation (GrFFF). This is a low-cost, fully biocompatible method with low instrumental and training investments for flow-assisted cell fractionation. The method allows obtaining pure cells without cell culture procedures as starting material for further analysis; for example, a proper amount of RNA can be extracted. The approach can be easily integrated into clinical and biomedical procedures.

Characterization of heat-induced changes in skim milk using asymmetrical flow field-flow fractionation coupled with multiangle laser light scattering

Separation and size measurement of protein particles are a relevant approach to monitor heat-induced changes in skim milk. Unfortunately, no method is currently available at low cost and without excessive preparation of the samples. Therefore, the present study aimed at evaluating the interest of asymmetrical flow field-flow fractionation (AFlFFF) coupled with multiangle laser light scattering (MALLS) for this purpose. Unheated and heated skim milk samples at pH 6.5 and 7.2 were prepared and comparatively analyzed using AFlFFF-MALLS, size exclusion chromatography (SEC-MALLS) and dynamic light scattering. The results showed that AFlFFF could evidence the conversion of the native whey proteins of unheated milk into heat-induced whey protein/κ-casein complexes in the serum phase of milk and possibly on the surface of the casein micelles. The pH-induced changes in the partition of the complexes between the serum and the micellar phases could also be observed. The results therefore showed the interest of AFlFFF-MALLS to monitor the heat-induced changes in particle sizes in skim milk and to separate the different protein components of unheated and heated skim milk.

Characterization of magnetic nanoparticles using programmed quadrupole magnetic field-flow fractionation

Quadrupole magnetic field-flow fractionation is a relatively new technique for the separation and characterization of magnetic nanoparticles. Magnetic nanoparticles are often of composite nature having a magnetic component, which may be a very finely divided material, and a polymeric or other material coating that incorporates this magnetic material and stabilizes the particles in suspension. There may be other components such as antibodies on the surface for specific binding to biological cells, or chemotherapeutic drugs for magnetic drug delivery. Magnetic field-flow fractionation (MgFFF) has the potential for determining the distribution of the magnetic material among the particles in a given sample. MgFFF differs from most other forms of field-flow fractionation in that the magnetic field that brings about particle separation induces magnetic dipole moments in the nanoparticles, and these potentially can interact with one another and perturb the separation. This aspect is examined in the present work. Samples of magnetic nanoparticles were analysed under different experimental conditions to determine the sensitivity of the method to variation of conditions. The results are shown to be consistent and insensitive to conditions, although magnetite content appeared to be somewhat higher than expected.

Application of asymmetric flow-field flow fractionation to the characterization of colloidal dispersions undergoing aggregation

The characterization of complex colloidal dispersions is a relevant and challenging problem in colloidal science. In this work, we show how asymmetric flow-field flow fractionation (AF4) coupled to static light scattering can be used for this purpose. As an example of complex colloidal dispersions, we have chosen two systems undergoing aggregation. The first one is a conventional polystyrene latex undergoing reaction-limited aggregation, which leads to the formation of fractal clusters with well-known structure. The second one is a dispersion of elastomeric colloidal particles made of a polymer with a low glass transition temperature, which undergoes coalescence upon aggregation. Samples are withdrawn during aggregation at fixed times, fractionated with AF4 using a two-angle static light scattering unit as a detector. We have shown that from the analysis of the ratio between the intensities of the scattered light at the two angles the cluster size distribution can be recovered, without any need for calibration based on standard elution times, provided that the geometry and scattering properties of particles and clusters are known. The nonfractionated samples have been characterized also by conventional static and dynamic light scattering to determine their average radius of gyration and hydrodynamic radius. The size distribution of coalescing particles has been investigated also through image analysis of cryo-scanning electron microscopy (SEM) pictures. The average radius of gyration and the average hydrodynamic radius of the nonfractionated samples have been calculated and successfully compared to the values obtained from the size distributions measured by AF4. In addition, the data obtained are also in good agreement with calculations made with population balance equations.

Magnetic nanoparticle drug carriers and their study by quadrupole magnetic field-flow fractionation

Magnetic nanoparticle drug carriers continue to attract considerable interest for drug targeting in the treatment of cancers and other pathological conditions. The efficient delivery of therapeutic levels of drug to a target site while limiting nonspecific, systemic toxicity requires optimization of the drug delivery materials, the applied magnetic field, and the treatment protocol. The history and current state of magnetic drug targeting is reviewed. While initial studies involved micrometer-sized and larger carriers, and work with these microcarriers continues, it is the sub-micrometer carriers or nanocarriers that are of increasing interest. An aspect of magnetic drug targeting using nanoparticle carriers that has not been considered is then addressed. This aspect involves the variation in the magnetic properties of the nanocarriers. Quadrupole magnetic field-flow fractionation (QMgFFF) is a relatively new technique for characterizing magnetic nanoparticles. It is unique in its capability of determining the distribution in magnetic properties of a nanoparticle sample in suspension. The development and current state of this technique is also reviewed. Magnetic nanoparticle drug carriers have been found by QMgFFF analysis to be highly polydisperse in their magnetic properties, and the strength of response of the particles to magnetic field gradients is predicted to vary by orders of magnitude. It is expected that the least magnetic fraction of a formulation will contribute the most to systemic toxicity, and the depletion of this fraction will result in a more effective drug carrying material. A material that has a reduced systemic toxicity will allow higher doses of cytotoxic drugs to be delivered to the tumor with reduced side effects. Preliminary experiments involving a novel method of refining a magnetic nanoparticle drug carrier to achieve this result are described. QMgFFF is used to characterize the refined and unrefined material.

Colloidal transport of uranium in soil: Size fractionation and characterization by field-flow fractionation-multi-detection

The aim of this study was to characterize colloids associated with uranium by using an on-line fractionation/multi-detection technique based on asymmetrical flow field-flow fractionation (As-Fl-FFF) hyphenated with UV detector, multi angle laser light scattering (MALLS) and inductively coupling plasma-mass spectrometry (ICP-MS). Moreover, thanks to the As-Fl-FFF, the different colloidal fractions were collected and characterized by a total organic carbon analyzer (TOC). Thus it is possible to determine the nature (organic or inorganic colloids), molar mass, size (gyration and hydrodynamic radii) and quantitative uranium distribution over the whole colloidal phase. In the case of the site studied, two populations are highlighted. The first population corresponds to humic-like substances with a molar mass of (1500+/-300)gmol(-1) and a hydrodynamic diameter of (2.0+/-0.2)nm. The second one has been identified as a mix of carbonated nanoparticles or clays with organic particles (aggregates and/or coating of the inorganic particles) with a size range hydrodynamic diameter between 30 and 450nm. Each population is implied in the colloidal transport of uranium: maximum 1% of the uranium content in soil leachate is transported by the colloids in the site studied, according to the depth in the soil. Indeed, humic substances are the main responsible of this transport in sub-surface conditions whereas nanoparticles drive the phenomenon in depth conditions.

Depolymerization study of sodium hyaluronate by flow field-flow fractionation/multiangle light scattering

Thermal depolymerization of ultrahigh-molecular-weight (UHMW) sodium hyaluronate (NaHA) was studied systematically by using frit-inlet asymmetrical flow field-flow fractionation/multiangle light scattering/differential refractive index (FI-AFlFFF/MALS/DRI). FI-AFlFFF was utilized for the size separation of NaHA samples which had been thermally degraded for varied treatment times, followed by light-scattering detection to determine MW and structural information of degraded NaHA products. Analysis of NaHA products showed time-dependent depolymerization of raw molecules into smaller-MW components, as well as unfolding of compact structures of UHMW NaHA. To determine whether the observed decrease in MW of sodium hyaluronate originated from the chain degradation of UHMW molecules or from dissociation of entangled complex particles that may have been formed by intermolecular association, narrow size fractions (1 x 10(7)-6 x 10(7) and >6 x 10(7) MW) of NaHA molecules were collected during FlFFF separation and followed by thermal treatment. Subsequent FI-AFlFFF/MALS analysis of collected fractions after thermal treatment suggested that the ultrahigh-MW region (>10(7) Da) of NaHA is likely to result from supermolecular structures formed by aggregation of large molecules.

A new method for high-resolution methane measurements on polar ice cores using continuous flow analysis

Methane (CH4) is the second most important anthropogenic greenhouse gas in the atmosphere. Rapid variations of the CH4 concentration, as frequently registered, for example, during the last ice age, have been used as reliable time markers for the definition of a common time scale of polar ice cores. In addition, these variations indicate changes in the sources of methane primarily associated with the presence of wetlands. In order to determine the exact time evolution of such fast concentration changes, CH4 measurements of the highest resolution in the ice core archive are required. Here, we present a new, semicontinuous and field-deployable CH4 detection method, which was incorporated in a continuous flow analysis (CFA) system. In CFA, samples cut along the axis of an ice core are melted at a melt speed of typically 3.5 cm/min. The air from bubbles in the ice core is extracted continuously from the meltwater and forwarded to a gas chromatograph (GC) for high-resolution CH4 measurements. The GC performs a measurement every 3.5 min, hence, a depth resolution of 15 cm is achieved atthe chosen melt rate. An even higher resolution is not necessary due to the low pass filtering of air in ice cores caused by the slow bubble enclosure process and the diffusion of air in firn. Reproducibility of the new method is 3%, thus, for a typical CH4 concentration of 500 ppb during an ice age, this corresponds to an absolute precision of 15 ppb, comparable to traditional analyses on discrete samples. Results of CFA-CH4 measurements on the ice core from Talos Dome (Antarctica) illustrate the much higher temporal resolution of our method compared with established melt-refreeze CH4 measurements and demonstrate the feasibility of the new method.

Isolation and analyses of enriched populations of male mouse germ cells by sedimentation velocity: the centrifugal elutriation

The studies of molecular events that occur in single cell types within a tissue often require the disaggregation of the tissue into a single cell suspension, followed by isolation of distinct cell populations. The germinal epithelium of mammals is composed of several cell types, which divide mitotically, before entering meiosis. In this chapter, we describe the isolation of five mouse germ-cell fractions by centrifugal elutriation, and characterize them by their DNA content (flow cytometry), cell morphology (DAPI staining of nuclei, Giemsa staining of squashed cells) and deposition of stage-specific meiotic markers (SYCP3, H1t, SAM68) on chromosome spreads and whole cells. Within 2 h it is possible to obtain enriched populations of elongated spermatids (up to approximately 50% of the fraction), round spermatids (up to approximately 80%), primary spermatocytes (up to approximately 89%), and secondary spermatocytes (up to approximately 17%). Furthermore, most of the collected spermatocytes of the primary spermatocyte fraction are in early-mid pachytene stage as judged by chromosome spreads, enriched up to approximately 89%. Elutriation and techniques used for characterization of germ cell fractions are described.

Enrichment of putative stem cells from adipose tissue using dielectrophoretic field-flow fractionation

We have applied the microfluidic cell separation method of dielectrophoretic field-flow fractionation (DEP-FFF) to the enrichment of a putative stem cell population from an enzyme-digested adipose tissue derived cell suspension. A DEP-FFF separator device was constructed using a novel microfluidic-microelectronic hybrid flex-circuit fabrication approach that is scaleable and anticipates future low-cost volume manufacturing. We report the separation of a nucleated cell fraction from cell debris and the bulk of the erythrocyte population, with the relatively rare (<2% starting concentration) NG2-positive cell population (pericytes and/or putative progenitor cells) being enriched up to 14-fold. This work demonstrates a potential clinical application for DEP-FFF and further establishes the utility of the method for achieving label-free fractionation of cell subpopulations.

Continuous flow separations in microfluidic devices

Biochemical sample mixtures are commonly separated in batch processes, such as filtration, centrifugation, chromatography or electrophoresis. In recent years, however, many research groups have demonstrated continuous flow separation methods in microfluidic devices. Such separation methods are characterised by continuous injection, real-time monitoring, as well as continuous collection, which makes them ideal for combination with upstream and downstream applications. Importantly, in continuous flow separation the sample components are deflected from the main direction of flow, either by means of a force field (electric, magnetic, acoustic, optical etc.), or by intelligent positioning of obstacles in combination with laminar flow profiles. Sample components susceptible to deflection can be spatially separated. A large variety of methods has been reported, some of these are miniaturised versions of larger scale methods, others are only possible in microfluidic regimes. Researchers now have a diverse toolbox to choose from and it is likely that continuous flow methods will play an important role in future point-of-care or in-the-field analysis devices.

Sedimentation field flow fractionation of immunoglobulin A coated polystyrene beads

The amount of immunoglobulin A (IgA) adsorbed on the surface of two different samples of polystyrene (PS) microbeads was evaluated using differential sedimentation field flow fractionation (SdFFF) analyses. For the first time, the SdFFF separations obtained by using, as mobile phase, solutions common to many biochemical procedures and applications have been compared and discussed. Good separation results were achieved in the different carriers, and the SdFFF gave equivalent mass per particle values in all carriers provided that the pH and ionic strength conditions of the eluents were well controlled. The IgA adsorption process onto PS occurred by maintaining unaltered the capacity of the PS-IgA substrate to selectively recognize anti-IgA (aIgA), as proven by elution of the ternary complex PS-IgA-aIgA and from the monitored lack of reaction when the PS-IgA was placed in contact with aIgE.

Free Flow Acoustophoresis: Microfluidic-Based Mode of Particle and Cell Separation

A novel method, free flow acoustophoresis (FFA), capable of continuous separation of mixed particle suspensions into multiple outlet fractions is presented. Acoustic forces are utilized to separate particles based on their size and density. The method is shown to be suitable for both biological and nonbiological suspended particles. The microfluidic separation chips were fabricated using conventional microfabrication methods. Particle separation was accomplished by combining laminar flow with the axial acoustic primary radiation force in an ultrasonic standing wave field. Dissimilar suspended particles flowing through the 350-microm-wide channel were thereby laterally translated to different regions of the laminar flow profile, which was split into multiple outlets for continuous fraction collection. Using four outlets, a mixture of 2-, 5-, 8-, and 10-microm polystyrene particles was separated with between 62 and 94% of each particle size ending up in separate fractions. Using three outlets and three particle sizes (3, 7, and 10 microm) the corresponding results ranged between 76 and 96%. It was also proven possible to separate normally acoustically inseparable particle types by manipulating the density of the suspending medium with cesium chloride. The medium manipulation, in combination with FFA, was further used to enable the fractionation of red cells, platelets, and leukocytes. The results show that free flow acoustophoresis can be used to perform complex separation tasks, thereby offering an alternative to expensive and time-consuming methods currently in use.

Characterization of high molecular weight polyethylenes using high temperature asymmetrical flow field-flow fractionation with on-line infrared, light scattering, and viscometry detection

High temperature asymmetrical flow field-flow fractionation (HTAF4) coupled to infrared (IR), multi-angle light scattering (MALS), and viscometry (Visc) detection is introduced as a tool for the characterization of high molecular weight polyethylenes. The high molecular weight fraction strongly affects the rheological behaviour and processability of polyethylene materials and can often not be accurately resolved by current technology such as high temperature size-exclusion chromatography (HTSEC). Molecular weight (M), radius of gyration (Rg), and intrinsic viscosity [eta] of linear high density polyethylene (HDPE) and branched low density polyethylene (LDPE) samples are studied in detail by HTAF4 and are compared to HTSEC. HTAF4 showed a better separation and mass recovery than HTSEC for very high molecular weight fractions in HDPE and LDPE samples. As no stationary phase is present in an HTAF4 channel, the technique does not show the typical drawbacks associated with HTSEC analysis of high molecular weight polyethylenes, such as, exclusion effects, shear degradation, and anomalous late elution of highly branched material. HTAF4 is applied to study the relation between the molecular weight and the zero shear viscosity eta0 for high molecular weight HDPE. It was found that the zero shear viscosity values predicted from HTAF4 results are in good qualitative agreement with measured values obtained from dynamic mechanical spectroscopy (DMS) experiments, whereas eta0 values predicted from HTSEC do not show a strong correlation. The low molecular weight cutoff of HTAF4 is approximately 5x10(4) as a result of relatively large pores in the HTAF4 channel membrane. HTAF4 is, therefore, currently not suited to analyze low molecular weight materials.

Miniaturized asymmetrical flow field-flow fractionation: Application to biological vesicles

Asymmetrical flow field-flow fractionation (AFlFFF) has been carried out in a miniaturized channel by reducing the channel dimensions. Performance of the miniaturized AFlFFF (mAFlFFF) channel was evaluated with standard proteins and polystyrene latex spheres from nanometer to micrometer size. By reducing the channel dimension, proteins or particulate materials can be separated within a few minutes without a significant loss in resolution. The mAFlFFF channel was applied for the separation of exosomes harvested from immortalized human mesenchymal stem cell line. It shows a potential to fractionate exosome vesicles according to sizes which can be useful for proteomic studies in relation to immunotherapeutic applications.

Hollow-fiber flow field-flow fractionation: a gentle separation method for mass spectrometry of native proteins

Low-impact ionization sources like electrospray ionization (ESI) and matrix-assisted, laser desorption/ionization (MALDI) equipped with time-of-flight (TOF) mass analyzers provide intact protein analysis over a very wide molar mass range. ESI/TOFMS provides also indications on the higher-order structure of intact proteins and non-covalent protein complexes. However, direct analysis of intact proteins mixtures in real samples shows limited success, mainly because spectra become very complex to interpret. This is also due to sample contaminants, and to the mechanism of competitive ionization in ESI or MALDI. Rapid and efficient sample clean-up and separation methods can significantly enhance the power of TOFMS for intact protein analysis. However, if protein native conditions want to be maintained, the methods should affect neither the three-dimensional structure nor the non-covalent chemistry of the proteins. Reversed-phase (RP) HPLC, size-exclusion chromatography (SEC), and capillary zone electrophoresis (CZE) are on-line or off-line coupled to ESI/TOFMS or MALDI/TOFMS. In fact, these separation methods often show limitations when applied to the analysis of native proteins. Organic modifiers and saline buffers are required in the case of RP HPLC or CZE. They can induce protein degradation or affect ionization when MS is performed after separation. High voltages used in CZE can contribute to alter proteins from their native form. In the case of high molar mass proteins, SEC is scarcely selective, and barely able to detect protein aggregates. Sample entanglement/adsorption on the stationary phase can also occur.

Sedimentation field flow fractionation monitoring of bimodal wheat starch amylolysis

Enzymatic starch granule hydrolysis is one of the most important reactions in many industrial processes. In this study, we investigated the capacity of sedimentation field flow fractionation (SdFFF) to monitor the amylolysis of a bimodal starch population: native wheat starch. Results demonstrated a correlation between fractogram changes and enzymatic hydrolysis. Furthermore, SdFFF was used to sort sub-populations which enhanced the study of granule size distribution changes occurring during amylolysis. These results show the interest in coupling SdFFF with particle size measurement methods to study complex starch size/density modifications associated to hydrolysis. These results suggested different applications such as the association of SdFFF with structural investigations to better understand the specific mechanisms of amylolysis or starch granule structure.

Pre-apoptotic sub-population cell sorting from diosgenin apoptosis induced 1547 cells by Sedimentation Field-Flow Fractionation

Apoptosis is one of the most important phenomena in cell biology. Pre-apoptotic cells, defined as cells engaged in early stages of apoptosis, could be used as a cellular tool to study apoptosis pathways. The human 1547 osteosarcoma cell line and diosgenin (a plant steroid) association was selected as an in vitro cellular apoptosis model. In a previous study, using this model, we demonstrated that SdFFF monitored apoptosis induction as early as 6h after incubation. In this study, we investigated the capacity of Sedimentation Field-Flow Fractionation (SdFFF) to sort an enriched population of pre-apoptotic cells from 1547 cells incubated for 6 h with 40 microM diosgenin. In that way, two different separation devices which differed especially in channel thickness, 125 and 175 microm, were used and compared. Results showed, for the first time, that SdFFF is an effective method to obtain an enriched pre-apoptotic sub-population. These results suggest, as a new application, that SdFFF could be an included tool in the study of apoptotic mechanisms or the kinetic action of apoptotic drugs.

Increasing the Sensitivity of Asymmetrical Flow Field-Flow Fractionation: Slot Outlet Technique

A new enrichment approach is described to improve the sensitivity of the asymmetrical flow field-flow fractionation, with and without ICPMS online coupling for elemental detection. For the slot outlet technique, a part of the laminar carrier stream is removed through an additional pump. This allowed an enrichment of the colloidal particles in the separation channel up to a factor of 14. Additional improvements of the separation efficiency permitted us to separate colloids with differences in their molecular masses of only 2 kDa. Different polymer standards, proteins, and synthesized tracer colloids, as well as real samples (wastewater, liquid manure, serums) were used to assess the performance of the new technique.

Effect of dissolution temperature on the structures of sodium hyaluronate by flow field-flow fractionation/multiangle light scattering

Molecular weight distribution (MWD) and structural deformation of ultrahigh molecular weight (MW) sodium hylaluronate (10(5)-10(8) g/mol) were studied under different sample dissolution temperature conditions, using on-line flow field-flow fractionation (FlFFF) and multiangle light scattering (MALS). Sodium hyaluronate (NaHA) materials from sarcoma fluid have been studied by dissolving them in water at three different temperature conditions (5 degrees C, 50 degrees C, and 90 degrees C). Frit inlet asymmetrical flow field-flow fractionation (FI-AFlFFF), with field programming, was utilized for the separation of NaHA by MW, and on-line observation of light scattering of fractionated NaHA by MALS was performed in order to determine the MWD and molecular conformation. In these experiments, NaHA molecules exhibited an extended structure from a formerly rather compact geometry when the dissolving temperature was raised to 90 degrees C. This study also showed a clear difference in the MWD of NaHA when a preliminary filtration process was applied.

Field-flow fractionation of proteins, polysaccharides, synthetic polymers, and supramolecular assemblies

This review summarizes developments and applications of flow and thermal field-flow fractionation (FFF) in the areas of macromolecules and supramolecular assemblies. In the past 10 years, the use of these FFF techniques has extended beyond determining diffusion coefficients, hydrodynamic diameters, and molecular weights of standards. Complex samples as diverse as polysaccharides, prion particles, and block copolymers have been characterized and processes such as aggregation, stability, and infectivity have been monitored. The open channel design used in FFF makes it a gentle separation technique for high- and ultrahigh-molecular weight macromolecules, aggregates, and self-assembled complexes. Coupling FFF with other techniques such as multiangle light scattering and MS provides additional invaluable information about conformation, branching, and identity.

Size characterization of green fluorescent protein inclusion bodies in E. coli using asymmetrical flow field-flow fractionation–multi-angle light scattering

The goal of this study was to investigate the applicability of asymmetrical flow field-flow fractionation-multi-angle light scattering (AsFlFFF-MALS) for size analysis of green fluorescent protein inclusion bodies (GFPIBs). The size distributions of GFPIBs prepared by various culture conditions were determined. For GFPIBs prepared at 37 degrees C the peak maximum hydrodynamic diameter (d(H)) first increased and then decreased with the increase of the induction times in the presence of 0.1 and 2 mM isopropyl-beta-D-thiogalactoside (IPTG). For GFPIBs prepared at 30 degrees C the peak maximum d(H) was constant at about 700 nm irrespectively of the induction times and IPTG concentrations.

Miniaturization of asymmetrical flow field-flow fractionation and application to studies on lipoprotein aggregation and fusion

Asymmetrical flow field-flow fractionation (AsFlFFF), a technique that provides direct measurement of particle size and diffusion coefficient, is converted into miniaturized scale. In comparison with conventional AsFlFFF, the separation of proteins in miniaturized AsFlFFF is achieved within shorter time periods, with smaller sample amounts, and with lower mobile phase consumption. Minimization of the overloading and optimization of the separation efficiency are prerequisites to good results. Miniaturized AsFlFFF is applied to the measurement of particle sizes of high-density lipoprotein (HDL), low-density lipoprotein (LDL), and very low-density lipoprotein (VLDL). The average hydrodynamic diameters at pH 7.4 in 8.5mM phosphate buffer containing 1mM EDTA and 150 mM NaCl are 8.6+/-0.5, 11.2+/-0.2, 22.1+/-0.7, and 48.9+/-7.5 nm for subgroups HDL3, HDL2, LDL, and VLDL, respectively. In addition, the effect of different factors on the aggregation and fusion of LDL particles is studied. LDL particle sizes are unaffected by the addition of up to 300 mM NaCl and by an increase of the carrier solution pH from 3.2 to 7.4, but treatment of LDL with alpha-chymotrypsin, sphingomyelinase, or copper sulfate leads to the formation of aggregated and fused LDL particles.

Electric Circuit Model for Electrical Field Flow Fractionation

In electrical field flow fractionation (EFFF or ElFFF), an electric potential is applied across a narrow gap filled with a weak electrolyte fluid. Charge buildup at the two poles (electrodes) and the formation of an electric double layer shields the channel, making the effective field in the bulk fluid very weak. Recent computational research suggests that pulsed field protocols, however, should improve retention and may enhance separation in EFFF through systematic disruptions of the double layer resulting in a stronger effective field in the bulk fluid. Improved retention has already been demonstrated experimentally. Accurate modeling and subsequent device optimization and design, however, depends, in part, on formulating a suitable model for the capacitative response of the channel and double layer at the electrode surfaces. Early models do not correctly describe experimentally observed current-time response and are not physically meaningful even when accurate mathematical fits of the data are realized. A new model and conceptual framework based on electrical resistance and capacitance variations of the double layer is suggested here. Physical interpretations of the electrical response have been developed and compared to published experimental data sets.

Continuous flow microextraction combined with high-performance liquid chromatography for the analysis of pesticides in natural waters

Continuous flow microextraction (CFME) combined with high-performance liquid chromatography-ultraviolet (HPLC-UV) detection has been applied to the analysis of five widely used pesticides, simazine, fensulfothion, etridiazole, mepronil and bensulide, present at trace levels in water samples. CFME employs a single organic solvent drop positioned at the tip of a polyether ether ketone (PEEK) tubing, which is immersed in a continuous flowing aqueous sample solution in a 0.5-ml glass chamber. The PEEK tubing acts as the organic drop holder and fluid delivery duct. Analytes are partitioned between the organic drop and the bulk sample solution. Important extraction factors including type of solvent, its volume, sample solution flow rate, extraction time, its pH and addition of salt were investigated. All pesticides exhibit good linearity in the investigated concentration range of 25-250 ng ml(-1) with coefficients of determination (R2) ranging from 0.9879 to 0.9999 under the optimized conditions. Detection limits lower than 4 ng ml(-1) were obtained for all analytes. The method was evaluated by analyzing natural water sample collected from a reservoir in Singapore. This study for the first time demonstrated the compatibility of CFME procedure and HPLC separation.

Comparative study of biological nutrient removal (BNR) processes with sedimentation and membrane-based separation

A membrane-enhanced biological phosphorus removal (MEBPR) process was operated in parallel with a conventional EBPR (CEBPR) process under challenging operating conditions to uncover fundamental differences in their ability to remove chemical oxygen demand (COD), nitrogen (N), and phosphorus (P) from municipal wastewater. Both systems exhibited the same potential to achieve excellent soluble-P removal when a favorable COD to P ratio was maintained in the influent. The MEBPR train generated a superior effluent quality when measured as total P. The CEBPR effluent contained significantly lower levels of nitrates due to the extra denitrification occurring in the sludge blanket of the secondary clarifier. The observed sludge yield in the MEBPR system was estimated to be between 0.23 and 0.28 g VSS/g COD, and this was 15% lower than the CEBPR sludge yield. When the influent volatile fatty acids (VFAs) became limiting, the CEBPR train exhibited better performance in the removal of soluble-P, due to the higher observed sludge yield and an overall greater denitrification activity that led to a more efficient use of VFAs in the anaerobic zone. After experiencing a severe deterioration of the biological P activity in both processes, the MEBPR train exhibited faster recovery than the CEBPR side. In this experimental work, it was demonstrated that an MEBPR process can sustain long-term satisfactory bio-P performance at HRTs as low as 7 h. However, the lower sludge yield and the reduced denitrification capacity are two important factors that impact the design of high rate membrane-assisted biological nutrient removal (BNR) processes.

Performance of hollow-fiber flow field-flow fractionation in protein separation

Since hollow-fiber flow field-flow fractionation (HF FIFFF) utilizes a cylindrical channel made of a hollow-fiber membrane, which is inexpensive and simple in channel assembly and thus disposable, interests are increasing as a potential separation device in cells, proteins, and macromolecules. In this study, performance of HF FIFFF of proteins is described by examining the influence of flow rate conditions and length of fiber (polyacrylonitrile or PAN in this work) on sample recovery as well as experimental plate heights. The interfiber reproducibility in terms of separation time and recovery was also studied. Experiments showed that sample recovery was consistent regardless of the length of fiber when the effective field strength (equivalent to the mean flow velocity at the fiber wall) and the channel void time were adjusted to be equivalent for channels of various fiber lengths. This supported that the majority of sample loss in HF FIFFF separation of apoferritin and their aggregates may occur before the migration process. It is finally demonstrated that HF FIFFF can be applied for characterizing the reduction in Stokes' size of low density lipoproteins from blood plasma samples obtained from patients having coronary artery disease and from healthy donors.

Field programming in frit inlet asymmetrical flow field-flow fractionation/multiangle light scattering: Application to sodium hyaluronate

The capability of field-programmed separation in frit inlet asymmetrical flow field-flow fractionation (FI-AFlFFF) has been examined for separating a high molecular weight sodium hyaluronate (NaHA) by varying the field programming parameters. Experiments were performed with on-line coupling of the field programming FI-AFlFFF and multiangle light scattering (MALS) detection. Sample relaxation, a pre-requisite step to establish equilibrium states of sample materials prior to the beginning of separation in most forms of FFF techniques, is obtained by hydrodynamically in FI-AFlFFF without stopping the migration flow. Thus, the procedures of sample injection -- hydrodynamic relaxation -- separation in FI-AFlFFF are continuously achieved without halting the sample migration. In this study, field programming in FI-AFlFFF was investigated for the separation of NaHA, water-soluble polysaccharides, by examining the influence of field decay pattern, initial field strength condition, and ionic strength of carrier solution on the successful separation of a degraded NaHA sample. Results were compared with molecular weight calculations of eluting materials among different field programming conditions from multiangle light scattering (MALS) signals. It was found that when the field programming was utilized in FI-AFlFFF, a proper selection of initial cross-flow rate, the field decay pattern, and an appropriate control of final field strength needed to be carefully selected in achieving a successful separation of a broad molecular weight water-soluble polymer sample.

Cell Sorting by One Gravity SPLITT Fractionation

The need for innovative separative techniques suitable for the fractionation of biomaterials prompted this investigation into the performance of the gravitational split-flow thin channel (G-SPLITT) system as a cell sorter. The rigorous mathematical description of the separation mechanism allows achievement of fast separation of several million myeloma cells from healthy splenocytes using flow conditions calculated from theory. Separation in G-SPLITT is based on differences in sedimentation rate. For accurate prediction of the optimal working conditions, this parameter was directly measured by cell tracking velocimetry rather than relying on a measure of diameter (by Multisizer) and an assumed density for each cell population. We also discuss the influence of different flow conditions on the effectiveness of separation.

Flow-based and sieving matrix-free DNA differentiation by a miniaturized field flow fractionation device

DNA separation is typically done by gel electrophoresis based on its charge property. In our previous work, we reported that dielectrophoresis could be used to manipulate polystyrene nanoparticles' motion by using a miniaturized electrical field flow fractionation device (micro-EFFF) with a segmented electrode operated under a pulsed voltage (PV). In this work, we report the manipulation and separation of DNA molecules using the micro-EFFF. DNA motion was in situ visualized inside the device. Results revealed that dielectrophoresis governed DNA motion, which was strongly correlated with the pulse frequency but not the duty cycle of a PV. A longer retention time of DNA molecules was measured under a PV. The retention time increased with the length of DNA molecules. As the micro-EFFF is flow-based and sieving-matrix-free, it has a potential to be applied to sample preparation in a micrototal analysis system or when fractionated molecules are needed for downstream analysis.

The use of asymmetrical flow field-flow fractionation in pharmaceutics and biopharmaceutics

Field-flow fractionation (FFF) is a family of flexible analytical fractionating techniques which have the advantage that the separation of analytes is achieved, solely through the interaction of the sample with an external, perpendicular physical field, rather than by the interaction with a stationary phase. The rapid progress in pharmaceutical biotechnology goes along with an increasing demand in potent, high-efficient analytical methods. Thus, FFF techniques are gaining increasing attention for their ability to separate and characterize populations of polymers, colloids and particles of up to about 100 microm in size. It is the intention of this review to provide an overview on common FFF techniques, to summarize inherent advantages and limitations and to introduce both established and challenging applications in the (bio)pharmaceutical field. Thereby, asymmetrical flow FFF is addressed predominantly, since it is the most versatile applicable FFF technique.

Miniaturization of Frit Inlet Asymmetrical Flow Field-Flow Fractionation

A miniaturized frit inlet asymmetrical flow field-flow fractionation (mFI-AFlFFF) channel has been constructed and tested for the separation of proteins. By scaling down the geometrical channel dimension of a conventional FI-AFlFFF system, flow rate ranges that can be manipulated were decreased to 20-30 microL/min, which reduces the injection amount of sample materials. The end effect contribution to plate height was evaluated by varying the inner diameter of the connection tubing between the injector and the channel inlet at various injection flow rates, and the results showed that the use of silica capillary tubing of the shortest possible distance is essential in reducing the initial band broadening prior to the sample injection to the microscale channel. The capability of the microFI-AFlFFF system was demonstrated with the separation of protein standards, polystyrenesulfonates, and ssDNA strains and for the characterization of replication protein A-ssDNA binding complex regulated by redox status.

Continuous particle separation through deterministic lateral displacement

We report on a microfluidic particle-separation device that makes use of the asymmetric bifurcation of laminar flow around obstacles. A particle chooses its path deterministically on the basis of its size. All particles of a given size follow equivalent migration paths, leading to high resolution. The microspheres of 0.8, 0.9, and 1.0 micrometers that were used to characterize the device were sorted in 40 seconds with a resolution of approximately 10 nanometers, which was better than the time and resolution of conventional flow techniques. Bacterial artificial chromosomes could be separated in 10 minutes with a resolution of approximately 12%.

Cell cytometry with a light touch: sorting microscopic matter with an optical lattice

Lab-on-a-chip design is a key technology for increasing both the reliability and the functionality of many different preparation and diagnostic techniques in biomedicine. The drive towards ever more integrated lab-on-a-chip designs requires increasingly complex microfluidic systems. In order to build these systems, non-invasive actuators such as pumps, filters and mixers are required. We have demonstrated microfluidic sorting based on a 3D interference pattern, formed from multiple coherent laser beams, which has the potential to fulfil all the above criteria. By interfering five laser beams from a fibre laser at 1070 nm, we have formed a 3D optical lattice. When particles flow through the optical lattice their trajectories depend upon the force exerted on the particle by the optical lattice, in combination with the drag force exerted by the fluid flow. Hence, with the strength of a particle's interaction with the lattice determining the total force exerted upon it, its trajectory is determined by its physical properties. These properties include refractive index, size and shape, giving a range of criteria with which to sort an analyte. We have shown separation at 45 degrees of polymer from silica microspheres (by refractive index), the separation of protein microcapsules and the sorting of erythrocytes from lymphocytes. The interference pattern can be tailored to the particles and if a blockage occurs, the laser can simply be switched off, unlike solid-state micro-sorters, so that no jamming occurs. Efficiencies in excess of 95% have been achieved.

Micro-thermal focusing field-flow fractionation

Focusing mechanism was effectively exploited to separate large (micrometer-size) particles by using new micro-thermal field-flow fractionation (micro-TFFF). It has been shown that the retention order of micrometer-size particles at high field strength can be explained by the mechanism of steric exclusion only at lowest flow rates of the carrier liquid. A simplistic, purely mechanical model of steric exclusion is not accurate to describe the retention at higher flow rates where the focusing phenomenon appears. Despite the fact that the thickness of the channel for micro-FFF cannot be reduced without taking into account a possible deterioration of the separation due to the contribution of "steric exclusion" mechanism, this paper demonstrates, in agreement with our previous results, that if the operational conditions were conveniently chosen, namely a low flow rate, a reasonable fit of the experimental retention data with the theory of steric exclusion mechanism in FFF was found and the separation of micron-size particles can be accomplished. However, high selectivity and resolution and high-speed separation were achieved if the focusing effect has clearly dominated the FFF mechanism. As a result, it seems that the micro-TFFF is the most universal technique which can be applied for the separation of the synthetic and natural macromolecules within an extended range of molar masses up to ultra-high molar masses and for the particles of various chemical nature and origin in a nano-size range as well as for large (micrometers) particles. Until nowadays, only sedimentation and flow field-flow fractionation techniques in so called "steric" modes were applied for the separations of large size particles. This application of micro-TFFF in focusing mode for the separation of large size particles is the first one described in the literature.

Microfluidic sorting in an optical lattice

The response of a microscopic dielectric object to an applied light field can profoundly affect its kinetic motion. A classic example of this is an optical trap, which can hold a particle in a tightly focused light beam. Optical fields can also be used to arrange, guide or deflect particles in appropriate light-field geometries. Here we demonstrate an optical sorter for microscopic particles that exploits the interaction of particles-biological or otherwise-with an extended, interlinked, dynamically reconfigurable, three-dimensional optical lattice. The strength of this interaction with the lattice sites depends on the optical polarizability of the particles, giving tunable selection criteria. We demonstrate both sorting by size (of protein microcapsule drug delivery agents) and sorting by refractive index (of other colloidal particle streams). The sorting efficiency of this method approaches 100%, with values of 96% or more observed even for concentrated solutions with throughputs exceeding those reported for fluorescence-activated cell sorting. This powerful, non-invasive technique is suited to sorting and fractionation within integrated ('lab-on-a-chip') microfluidic systems, and can be applied in colloidal, molecular and biological research.