Electrical Field-flow Fractionation Research Articles

Nanoparticle characterization by electrical field-flow fractionation and single particle inductively coupled plasma mass spectrometry

Electrical field-flow fractionation (ElFFF) is a sub-technique of field-flow fractionation utilized for separation of charged nanoparticles. ElFFF was applied for characterization of size and charge of nanoparticles by investigating the nanoparticle retention time. However, one of the parameters; i.e., size or charge of nanoparticles, must be known before characterizing another parameter. This work illustrates an application of normal ElFFF for nanoparticle characterization associated with single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) which was used for size determination. Six nanoparticles samples including 30 nm AuNPs stabilized by citrate, 60 nm AuNPs stabilized by citrate, mixture of 30 nm and 60 nm AuNPs stabilized by citrate, 60 nm silver nanoparticles (AgNPs) stabilized by polyethylene glycol (PEG), 100 nm AgNPs stabilized by citrate, and mixture of 60 nm AgNPs stabilized by PEG and 100 nm AgNPs stabilized by citrate were used as samples. The nanoparticles were prior separated in ElFFF system under 1.50 V applied voltage in deionized (DI) water carrier, then their fractions were collected for size determination using SP-ICP-MS. The charge, electrophoretic mobility, of nanoparticles was characterized by using the size determined from SP-ICP-MS and the retention time of nanoparticles via the ElFFF theoretical equation. The size and charge of nanoparticles characterized using ElFFF and SP-ICP-MS were in agreement with their size and charge reported in certificate. In addition, the size information obtained from ElFFF and SP-ICP-MS was applied for characterization of the layer thickness of stabilizing agent coated on nanoparticle surface of 60 nm AgNPs stabilized by PEG. With high sensitivity of inductively coupled plasma mass spectrometry (ICP-MS), this method shows potential use for characterization of nanoparticles in environmental system.

Insight into the formation and biological effects of natural organic matter corona on silver nanoparticles in water environment using biased cyclical electrical field-flow fractionation

Natural organic matter (NOM) readily interacts with nanoparticles, leading to the formation of NOM corona structures on their surface. NOM corona formation is closely related to the surface coatings and bioavailability of nanoparticles. However, the mechanism underlying NOM corona formation on silver nanoparticles (AgNPs) remains largely unknown due to the lack of effective analytical methods for identifying the changes in the AgNP surface. Herein, the separation ability of biased cyclical electrical field-flow fractionation (BCyElFFF) for same-sized polyvinyl pyrrolidone-coated and poly(ethylene glycol)-coated silver nanoparticles (AgNPs) with different electrophoretic mobilities was evaluated under various electrical conditions. Then, the mechanism behind the NOM corona formation on these AgNP surfaces was elucidated based on the changes in the elution time and off-line characterization of the collected fractions during their elution time in a BCyElFFF run. Finally, the survival rates of E. coli exposed to polyvinyl pyrrolidone-coated and poly(ethylene glycol)-coated AgNPs with or without NOM collected during repeated BCyElFFF runs were observed to increase with increasing NOM concentration, clearly demonstrating the negative effect of NOM corona structures on the bioavailability of AgNPs. These findings highlight the powerful separation and isolation ability of BCyElFFF in studying the transformation and fate of nanoparticles in aqueous environments.

Use of electrical field-flow fractionation for gold nanoparticles after improving separation efficiency by carrier liquid optimization

Electrical field-flow fractionation (ElFFF) is a useful separation technique for nanoparticles, however, it has been limited by polarization/electrical double layer formation which reduces an effective field for separation. With an appropriate direct current (DC) applied voltage, sodium carbonate, FL-70, Triton X-100 and acetonitrile were explored as additive substances for preparation of carrier liquid used in normal ElFFF to enhance an amplitude of effective field by their ionic redox-active species, ionic and nonionic surfactant and wide electrochemical potential window nonionic organic solvent properties, respectively. Effective field was indirectly measured in each carrier liquid by investigating retention behavior of polystyrene latex nanoparticles and gold nanoparticles. Effective field improvement was observed in all carrier liquid types (except FL-70) by which the highest effective field existed in 16 μM sodium carbonate at 1.70 V and 0.01% (V/V) Triton X-100 and 50% (V/V) acetonitrile at 1.90 V as compared to deionized water at 1.90 V. In addition, those carrier liquids were applied for separation of 5 nm and 15 nm gold nanoparticles mixture by which Triton X-100 exhibited the best separation resolution (Rs = 1.11).

Characterization of Human Glioblastoma versus Normal Plasma-Derived Extracellular Vesicles Preisolated by Differential Centrifugation Using Cyclical Electrical Field-Flow Fractionation.

Although many properties for small extracellular vesicles (sEVs, formerly termed "exosomes") isolated at ∼100 000g are known, a wide range of values are reported for their electrophoretic mobility (EM) measurements. This paper reports for the first time the effect of dilution on the EM of U87 glioblastoma cell-derived and plasma-derived sEVs and medium size EVs (mEVs, commonly termed "oncosomes") preisolated by differential centrifugation. Furthermore, the effect of resalting on the EM of sEVs and mEVs was evaluated. The EM of U87 sEVs and U87 mEVs showed an increase as the salt concentration decreased to 0.005% of the initial salt concentration. However, for the plasma sEVs and plasma mEVs, the electrophoretic mobility increased as the salt concentration decreased to 0.01% of the initial salt concentration and then increased to its initial value when the salt concentration decreased to 0.005% of the initial salt concentration. For both U87 and plasma sEVs and mEVs, the EM remained almost constant when the concentration of the particles changed and the salt concentration was kept the same as its initial value. This indicates that the EM of EVs is only a function of the salt concentration of the buffer and is independent of the concentration of the particles. The sEVs and mEVs were separated with cyclical ElFFF for the first time. The results indicate that ElFFF was able to fractionate the EVs, and a crescent-shaped trend was found for the retention time when the applied AC voltage was altered (increased).

Characterization and differential retention of Q beta bacteriophage virus-like particles using cyclical electrical field-flow fractionation and asymmetrical flow field-flow fractionation.

Virus-like particles (VLPs) are widely used in medicine, but can be difficult to characterize and isolate from aggregates. In this research, primarily cyclical electrical field-flow fractionation (CyElFFF) coupled with multi-angle light scattering (MALS), and dynamic light scattering (DLS) detectors, was used for the first time to perform size and electrical characterization of three different types of Q beta bacteriophage virus-like particles (VLPs): a blank Q beta bacteriophage which is denoted as VLP and two conjugated ones with different peptides. The CyElFFF results were verified with transmission electron microscopy (TEM). Asymmetrical flow field-flow fractionation (AF4) coupled with MALS was also applied using conditions similar to those used in the CyElFFF experiments, and the results of the two techniques were compared to each other. Using these techniques, the size and electrophoretic characteristics of the fractionated VLPs in CyElFFF were obtained. The results indicate that CyElFFF can be used to obtain a clear distribution of electrophoretic mobilities for each type of VLP. Accordingly, CyElFFF was able to differentially retain and isolate VLPs with high surface electric charge/electrophoretic mobility from the ones with low electric charge/electrophoretic mobility. Regarding the size characterization, the size distribution of the eluted VLPs was obtained using both techniques. CyElFFF was able to identify subpopulations that did not appear in the AF4 results by generating a shoulder peak, whereas AF4 produced a single peak. Different size characteristics of the VLPs appearing in the shoulder peak and the main peak indicate that CyElFFF was able to isolate aggregated VLPs from the monomers partially. Graphical abstract.

Characteristics of electrical field flow fractionation with chronoamperometry and electrochemical impedance

Electrical field flow fractionation (EFFF) is a particle separation method that employs an electrical field to cause particles in the carrier flow transferring in the vertical direction. The electrical characteristics of EFFF are one of the important aspects to explore electrical field how to work on the particle separation in EFFF channel. The equivalent electrical circuit model of EFFF channel was built. The experiments of chronoamperometry and electrochemical impedance spectroscopy (EIS) were conducted on the EFFF channel. The electrical circuit was utilised to fit the data of EIS experiments on EFFF channel. The fitting data were compared with the experimental data of EIS. The result indicates that the experimental data is highly quantified with the fitting data. It manifested that the equivalent electrical circuit reflected the electrical characteristics of the EFFF channel.

Exosome Isolation: Cyclical Electrical Field Flow Fractionation in Low-Ionic-Strength Fluids.

The influence of buffer substitution and dilution effects on exosome size and electrophoretic mobility were shown for the first time. Cyclical electrical field flow fractionation (Cy-El-FFF) in various substituted fluids was applied to exosomes and other particles. Tested carrier fluids of deionized (DI) water, 1× phosphate buffered saline (PBS), 0.308 M trehalose, and 2% isopropyl alcohol (IPA) influenced Cy-El-FFF-mediated isolation of A375 melanoma exosomes. All fractograms revealed a crescent-shaped trend in retention times with increasing voltage with the maximum retention time at ∼1.3 V AC. A375 melanoma exosome recovery was approximately 70-80% after each buffer substitution, and recovery was independent of whether the sample was substituted into 1× PBS or DI water. Exosome dilution in deionized water produced a U-shaped dependence on electrophoretic mobility. The effect of dilution using 1× PBS buffer revealed a very gradual change in electrophoretic mobility of exosomes from ∼-1.6 to -0.1 μm cm/s V, as exosome concentration was decreased. This differed from the use of DI water, where a large change from ∼-5.5 to -0.1 μm cm/s V over the same dilution range was observed. Fractograms of separated A375 melanoma exosomes in two substituted low-ionic-strength buffers were compared with synthetic particle fractograms. Overall, the ability of Cy-El-FFF to separate exosomes based on their size and charge is a highly promising, label-free approach to initially catalogue and purify exosome subtypes for biobanking as well as to enable further exosome subtype interrogations.

Effect of Ionic and Nonionic Carriers in Electrical Field-Flow Fractionation.

A major limitation of electrical field-flow fractionation (ElFFF) is the polarization of the electrodes that occurs when using an ionic carrier liquid. As there is great interest in using ElFFF with biological materials and biological materials typically have high ionic strengths and high osmotic concentrations, we explore the effect of concentration for phosphate buffered saline (PBS), a typical ionic medium for biological samples, and for two nonionic materials common in bioparticle analysis: isopropanol (IPA) and sucrose. Their effect on retention and separations in ElFFF for increasing concentrations was observed. The results suggest that modifying the carrier solution with PBS, sucrose, and/or IPA would enable characterization and separation of biological samples in ElFFF. Specifically, changes of elution time and electrical parameters such as current, conductivity, and bulk channel resistance were observed as functions of carrier ionic and osmotic strength for the different carrier additives. PBS can be used in the micromolar range, equivalent to about 0.1% 1× PBS (150 μM). These concentrations are far from the isotonic condition of PBS (∼ 150 mM) that is normally used with biological samples. However, the nonionic additive carriers IPA and sucrose show quality retention even when added in high concentrations. The results show that IPA could be used in ratios up to 60% and that sucrose can be used in concentrations up to 0.3 M. Concentrations of 2% IPA (0.26 M) and 0.30 M sucrose are biologically isotonic conditions (275-299 mOsm/kg), and retention was readily obtained in these conditions using both DC ElFFF and cyclical ElFFF (CyE1FFF). Carriers of this type may make it possible to use ElFFF with biological samples.

Particle Based Modeling of Electrical Field Flow Fractionation Systems

Electrical Field Flow Fractionation (ElFFF) is a sub method in the field flow fractionation (FFF) family that relies on an applied voltage on the channel walls to effect a separation. ElFFF has fallen behind some of the other FFF methods because of the optimization complexity of its experimental parameters. To enable better optimization, a particle based model of the ElFFF systems has been developed and is presented in this work that allows the optimization of the main separation parameters, such as electric field magnitude, frequency, duty cycle, offset, flow rate and channel dimensions. The developed code allows visualization of individual particles inside the separation channel, generation of realistic fractograms, and observation of the effects of the various parameters on the behavior of the particle cloud. ElFFF fractograms have been generated via simulations and compared with experiments for both normal and cyclical ElFFF. The particle visualizations have been used to verify that high duty cycle voltages are essential to achieve long retention times and high resolution separations. Furthermore, by simulating the particle motions at the channel outlet, it has been demonstrated that the top channel wall should be selected as the accumulation wall for cyclical ElFFF to reduce band broadening and achieve high efficiency separations. While the generated particle based model is a powerful tool to estimate the outcomes of the ElFFF experiments and visualize particle motions, it can also be used to design systems with new geometries which may lead to the design of higher efficiency ElFFF systems. Furthermore, this model can be extended to other FFF techniques by replacing the electrical field component of the model with the fields used in the other FFF techniques.

Biophysical Characterization of VLPs

Genetic Engineering & Biotechnology NewsVol. 35, No. 2 Bioprocessing TutorialBiophysical Characterization of VLPsAdvantages of Utilizing a Light-Scattering Toolbox in Vaccine DevelopmentDaniel SomeDaniel SomeDaniel Some, Ph.D., (E-mail Address: dsome@wyatt.com) is principal scientist at Wyatt Technology. Web: www.wyatt.comSearch for more papers by this authorPublished Online:13 Jan 2015https://doi.org/10.1089/gen.35.02.14AboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View articleFiguresReferencesRelatedDetailsCited byCurrent status and future challenges in transitioning to continuous bioprocessing of virus‐like particles30 June 2021 | Journal of Chemical Technology & Biotechnology, Vol. 97, No. 9Characterization and differential retention of Q beta bacteriophage virus-like particles using cyclical electrical field–flow fractionation and asymmetrical flow field–flow fractionation14 January 2020 | Analytical and Bioanalytical Chemistry, Vol. 412, No. 7Production of Well-Characterized Virus-like Particles in an Escherichia coli-Based Expression Platform for Preclinical Vaccine Assessments14 April 2016 Volume 35Issue 2Jan 2015 Information© 2015 by GEN PublishingTo cite this article:Daniel Some.Biophysical Characterization of VLPs.Genetic Engineering & Biotechnology News.Jan 2015.28-28.http://doi.org/10.1089/gen.35.02.14Published in Volume: 35 Issue 2: January 13, 2015PDF download

Circuit modification in electrical field flow fractionation systems generating higher resolution separation of nanoparticles

Compared to other sub-techniques of field flow fractionation (FFF), cyclical electrical field flow fractionation (CyElFFF) is a relatively new method with many opportunities remaining for improvement. One of the most important limitations of this method is the separation of particles smaller than 100nm. For such small particles, the diffusion rate becomes very high, resulting in severe reductions in the CyElFFF separation efficiency. To address this limitation, we modified the electrical circuitry of the ElFFF system. In all earlier ElFFF reports, electrical power sources have been directly connected to the ElFFF channel electrodes, and no alteration has been made in the electrical circuitry of the system. In this work, by using discrete electrical components, such as resistors and diodes, we improved the effective electric field in the system to allow high resolution separations. By modifying the electrical circuitry of the ElFFF system, high resolution separations of 15 and 40nm gold nanoparticles were achieved. The effects of applying different frequencies, amplitudes and voltage shapes have been investigated and analyzed through experiments.

Biased Cyclical Electrical Field Flow Fractionation for Separation of Sub 50 nm Particles

Cyclical electrical field flow fractionation (CyElFFF) is a technique for characterizing and separating nanoparticles based on their size and charge using cyclical electric fields. The high diffusion rate of nanoparticles has prevented CyElFFF from being applicable to particles smaller than 100 nm. In this work, the diffusion challenges associated with nanoparticles was resolved using biased cyclical electric fields. This new method, biased cyclical electrical field flow fractionation (BCyElFFF), achieves baseline separation of 15 and 40 nm gold nanoparticles. Theoretical considerations show that the optimal resolution is achieved when the applied bias yields electrical transport that counteracts the diffusive transport of nanoparticles. BCyElFFF greatly extends separation capabilities of the cyclical electrical field flow fractionation to sub 50 nm nanoparticles and provides a powerful alternative to other separation and characterization techniques capable of separating nanoparticles smaller than 50 nm.

Separation of Magnetic Nanoparticles by Cyclical Electrical Field Flow Fractionation

In this study, the potential of Cyclical Electrical Field Flow Fractionation (CyEFFF) for the separation of magnetic nanoparticles is investigated. We demonstrated for the first time that by the application of appropriate voltage waveforms, one can separate gold nanoparticles with sizes less than 50 nm. By using suitable voltage waveforms, the detrimental effect of the particle diffusion is suppressed and particles in the range of 10 nms can be fractionated. In addition, it is shown that CyEFFF is capable of separating lipid and polystyrene sulfonate coated magnetite nanoparticles with the same hydrodynamic radius of 50 nm.

Characterization of Polymerized Liposomes Using a Combination of dc and Cyclical Electrical Field-Flow Fractionation

Characterization of polymerized liposomes (PolyPIPosomes) was carried out using a combination of normal dc electrical field-flow fractionation and cyclical electrical field-flow fractionation (CyElFFF) as an analytical technique. The constant nature of the carrier fluid and channel configuration for this technique eliminates many variables associated with multidimensional analysis. CyElFFF uses an oscillating field to induce separation and is performed in the same channel as standard dc electrical field-flow fractionation separation. Theory and experimental methods to characterize nanoparticles in terms of their sizes and electrophoretic mobilities are discussed in this paper. Polystyrene nanoparticles are used for system calibration and characterization of the separation performance, whereas polymerized liposomes are used to demonstrate the applicability of the system to biomedical samples. This paper is also the first to report separation and a higher effective field when CyElFFF is operated at very low applied voltages. The technique is shown to have the ability to quantify both particle size and electrophoretic mobility distributions for colloidal polystyrene nanoparticles and PolyPIPosomes.

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.

A novel method for effective field measurements in electrical field‐flow fractionation

The electric field that drives separation and retention in electrical field flow fractionation (ElFFF) and cyclical electrical field-flow fractionation (CyElFFF) is a complex function of many parameters such as carrier ionic strength and pH, voltage, channel dimensions, flowrate, and electrode material. Currently there is no accurate or in situ method to measure the field during system operation. This paper introduces a technique to measure the effective electric field during ElFFF and CyElFFF operation using transient electrical spikes. With this technique we can determine the relationship between changes in carrier conductivity and flowrate during a run and their combined effect on effective field and retention in ElFFF. This technique can also be used to measure the voltage drop due to double layer capacitance in CyElFFF and the variation in effective field with frequency of the applied field. The measured effective fields for the CyElFFF and DC ElFFF techniques are also tested with a high ionic-strength buffer solution as carrier. For a high ionic-strength buffer, DC ElFFF generates a near-zero effective field (0.2% in 100 s), whereas CyElFFF can sustain much higher effective fields (~8%) even at relatively high voltages. The ability to measure the effective field allows for experiments to provide better data and for tuning and optimization of the separation run.

Characterization of a microscale thermal–electrical field-flow fractionation system

A microscale thermal–electrical field-flow fractionation (ThElFFF) channel is reported for the first time and preliminary characterization results show high retention at certain operating conditions including relatively high flow rates when compared to standard microscale electrical or thermal field-flow fractionation instruments. A new design is presented that simplifies manufacturing and assembly of the prototype and that can provide both an electrical field and a high temperature gradient (∼106°C/m). Monodisperse particle retention is carried out with polystyrene nanoparticle samples to characterize the device. Retention ratios as low as 0.045 are observed with the ThElFFF instrument. Size selectivity of 1.77 was achieved for ThElFFF. The comparison with theory shows a marked deviation from the existing theory. Separation of a mixture of polystyrene particles is demonstrated for the first time using a ThElFFF system by separating 130nm carboxylated polystyrene and 209nm polystyrene particles.

Nanoparticle Characterization by Cyclical Electrical Field-Flow Fractionation

In this work, the analytical potential of cyclical electrical field flow fractionation (CyElFFF) for nanomaterial and colloidal particle characterization has been experimentally demonstrated. Different operating parameters were investigated in order to evaluate their effect on the mechanisms of retention and fractionation power of CyElFFF. The voltage and frequency of the oscillating electrical field appeared to be the most influential parameters controlling the separation mode. Mobile phase flow rate was also found to be a key parameter controlling the fractionation efficiency. This work allowed the definition of operating conditions such that a reliable CyElFFF analysis could be performed on different nanoparticles on the basis of the direct comparison of their theoretical and experimental behavior. The results show that this technique in optimized conditions is a powerful tool for electrophoretic mobility based separation and characterization of various nanoparticles.

Enhancement of the Classification Performance of Electrical Field-Flow Fractionation Using Horizontal Electrophoresis

The purpose of the present study was to enhance the classification performance of electrical field-flow fractionation (EFFF). In recent research by this group, the surface potential of silica particles treated with a bead mill displayed size dependency—smaller particles had a more negative zeta potential. This phenomenon and the EFFF system were used to classify the particles, with the bottom and top plates of the EFFF channel serving as negative and positive electrodes, respectively.In the present study, improvements to the EFFF channel were carried out to enhance classification accuracy. Walls of deionized water were utilized to prevent particles from contacting the electrodes. Because vertical electrophoresis led to the disturbance of particle trajectories in the channel by gravitational sedimentation, horizontal electrophoresis was applied. Furthermore, hydrodynamic force was induced in the channel creating differing linear velocities of the slurry and the water at the inlet. As a result, 200-nm particles could be classified at an applied voltage of 5 V with high accuracy when compared with the previous method that used vertical electrophoresis.

Optimization of cyclical electrical field flow fractionation

Cyclical electrical field flow fractionation (CyElFFF) is a variation on electrical field flow fractionation (ElFFF) where cyclical electrical fields are used instead of steady DC fields to increase the effective field experienced by particles in the flow channel. Even though the effective field increases more than 20-fold compared to normal ElFFF, the retention and resolution in CyElFFF has not been shown to be better than in ElFFF. In this paper we report how one can optimize operational parameters in CyElFFF to obtain good retention and resolution in CyElFFF. The effects of offset voltage, frequency, flowrate, concentration of particles and sample size on retention, resolution and retained peak/void peak ratio have been observed. The results obtained from these experiments were analyzed and suggestions have been made to improve both retention and resolution. A 4-fold improvement in retention without a significant increase in band broadening is reported.