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1.
Electrophoresis ; 40(22): 2979-2987, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31478226

RESUMO

Low voltage, non-gassing electroosmotic pump (EOP) was assembled with poly(2-ethyl aniline) (EPANI)-Prussian blue nanocomposite electrode and commercially available hydrophilic PVDF membranes. The nanocomposite material combines excellent oxidation/reduction capacity of EPANI with exceptional stability by shuttling of proton between Prussian blue nanoparticles and EPANI redox matrix. The flow rate was highly dependent on the electrode composition but it was linear with applied voltage. The flow rate at 5 V for different nanocomposite, EPANI, EPANI-A, EPANI-B, and EPANI-C were 127.29, 187.41, 148.51, and 95.47 µL/min cm2 , respectively, which increases substantially with increase in the Prussian blue content. The obtained best electro osmotic flux was 43 µL/min/V/cm2 for EPANI-A. It was higher than most of the EOP assembled using polyquinone and polyanthraquinone redox polymers. The assembled EOP remained exceptionally stable until the electrode charge capacity was fully utilized. The best EOP produces a maximum stall pressure of 1.2 kPa at 2 V. These characteristics make it suitable for a variety of microfluidic/device applications.


Assuntos
Compostos de Anilina/química , Eletro-Osmose/métodos , Ferrocianetos/química , Nanocompostos/química , Eletrodos , Membranas Artificiais , Técnicas Analíticas Microfluídicas/métodos , Oxirredução , Polivinil/química
2.
Artigo em Inglês | MEDLINE | ID: mdl-31176269

RESUMO

Plant polyphenols can form functional coatings on various materials through self-polymerization. In this paper, a series of modified capillary columns, which possess diversity of charge characteristics for modulating electroosmotic flow (EOF), were prepared by one-step co-deposition of gallic acid (GA), a plant-derived polyphenol monomer, and branched polyethyleneimine (PEI). The physicochemical properties of the prepared columns were characterized by Fourier transform infrared spectroscopy (FT-IR), UV-Vis spectroscopy and scanning electron microscopy (SEM). The magnitude and direction of EOF of GA/PEI co-deposited columns were modulated by changing a series of coating parameters, such as post-incubation of FeCl3, co-deposition time, and deposited amounts of GA and PEI with different relative molecular mass (PEI-600, PEI-1800, PEI-10000, and PEI-70000). Furthermore, the separation efficiencies of the prepared GA/PEI co-deposited columns were evaluated by separations of small molecules, including organic acids, polar nucleotides, phenols, nucleic acid bases and nucleosides. Results indicated that modulating of EOF plays an important role in enhancing the separation performance and reversing the elution order of the analytes. Finally, the developed method was successfully applied to quantitative analysis of acidic compounds in four real samples. The recoveries were in the range of 73.5%-85.8% for citric acid, benzoic acid, sorbic acid, salicylic acid and ascorbic acid in beverage and fruit samples, 101.6%-104.9% for cinnamic acid, vanillic acid, and ferulic acid in Angelica sinensis sample, while 84.6%-97.8% for guanosine-5'-monophosphate, uridine-5'-monophosphate, cytosine-5'- monophosphate and adenosine-5'-monophosphate in Cordyceps samples. These results indicated that the co-deposition of plant polyphenol-inspired GA/PEI coatings can provide new opportunities for EOF modulation of capillary electrophoresis.


Assuntos
Eletrocromatografia Capilar/métodos , Eletro-Osmose/métodos , Ácido Gálico/química , Polietilenoimina/química , Eletrocromatografia Capilar/instrumentação , Eletro-Osmose/instrumentação , Peso Molecular , Ácidos Nucleicos/isolamento & purificação , Nucleosídeos/isolamento & purificação , Nucleotídeos/isolamento & purificação , Compostos Orgânicos/isolamento & purificação , Polimerização
3.
Electrophoresis ; 40(16-17): 2149-2156, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-30916400

RESUMO

In this work, an efficient electroosmotic pump (EOP) based on the ultrathin silica nanoporous membrane (u-SNM), which can drive the motion of fluid under the operating voltage as low as 0.2 V, has been fabricated. Thanks to the ultrathin thickness of u-SNM (∼75 nm), the effective electric field strength across u-SNM could be as high as 8.27 × 105 V m-1 in 0.4 M KCl when 1.0 V of voltage was applied. The maximum normalized electroosmotic flow (EOF) rate was as high as 172.90 mL/min/cm2 /V, which was larger than most of other nanoporous membrane based EOPs. In addition to the ultrathin thickness, the high porosity of this membrane (with a pore density of 4 × 1012 cm-2 , corresponding to a porosity of 16.7%) also contribute to such a high EOF rate. Moreover, the EOF rate was found to be proportional to both the applied voltage and the electrolyte concentration. Because of small electrokinetic radius of u-SNM arising from its ultrasmall pore size (ca. 2.3 nm in diameter), the EOF rate increased with increasing the electrolyte concentration and reached the maximum at a concentration of 0.4 M. This dependence was rationalized by the variations of both zeta potential and electrokinetic radius with the electrolyte concentration.


Assuntos
Eletro-Osmose/instrumentação , Membranas Artificiais , Nanoporos , Dióxido de Silício/química , Eletro-Osmose/métodos , Desenho de Equipamento , Modelos Químicos , Porosidade
4.
Anal Chim Acta ; 1057: 152-161, 2019 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-30832914

RESUMO

Successive multiple ionic-polymer layers (SMIL) coatings have been often used in capillary electrophoresis due to their simplicity to implement and regenerate. However, the performances of the separation are strongly dependent on the nature of the polyelectrolyte partners used to build the SMIL coating. In this work, we investigate new couples of polyelectrolytes that were not tested before: namely, polybrene (PB), quaternized diethylaminoethyl dextran (DEAEDq) and ε-poly(lysine) (ε-PLL), as polycations, in combination with poly(acrylic acid), dextran sulfate, poly(styrenesulfonate), poly(methacrylic acid) and poly(l-lysine citramide), as polyanions. Systematic study of intra- and inter-capillaries repeatabilities/reproducibilities was performed based on the determination of migration time, separation efficiency and electroosmotic mobility. Interestingly, the electroosmotic flow was found to vary with the nature of the polycation on a broad range of electroosmotic mobility decreasing in magnitude in the order of PB>ε-PLL > DEAEDq, whatever the polyanion associated. Application of the coatings to the separation of proteins is illustrated in a 0.5 M acetic acid BGE, including CE-MS separation of ribonuclease B-glycoforms of the same mass (positional or structural isomers).


Assuntos
Eletro-Osmose/métodos , Eletroforese Capilar , Polieletrólitos/química , Proteínas/análise , Proteínas/química , Animais
5.
Electrophoresis ; 40(10): 1387-1394, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30346029

RESUMO

Insulator-based dielectrophoresis has to date been almost entirely restricted to Newtonian fluids despite the fact that many of the chemical and biological fluids exhibit non-Newtonian characteristics. We present herein an experimental study of the fluid rheological effects on the electroosmotic flow of four types of polymer solutions, i.e., 2000 ppm xanthan gum (XG), 5% polyvinylpyrrolidone (PVP), 3000 ppm polyethylene oxide (PEO), and 200 ppm polyacrylamide (PAA) solutions, through a constriction microchannel under DC electric fields of up to 400 V/cm. We find using particle streakline imaging that the fluid elasticity does not change significantly the electroosmotic flow pattern of weakly shear-thinning PVP and PEO solutions from that of a Newtonian solution. In contrast, the fluid shear-thinning causes multiple pairs of flow circulations in the weakly elastic XG solution, leading to a central jet with a significantly enhanced speed from before to after the channel constriction. These flow vortices are, however, suppressed in the strongly viscoelastic and shear-thinning PAA solution.


Assuntos
Eletro-Osmose/métodos , Soluções/química , Resinas Acrílicas/química , Elasticidade , Eletro-Osmose/instrumentação , Técnicas Analíticas Microfluídicas/instrumentação , Polietilenoglicóis/química , Polissacarídeos Bacterianos/química , Povidona/química , Substâncias Viscoelásticas/química
6.
Methods Mol Biol ; 1906: 55-64, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30488384

RESUMO

Sample introduction is an important consideration in any microchip electrophoresis (ME) separation. The number of applications and level of complexity of ME devices continue to increase, but the introduction of sample into the separation channel has remained relatively constant. This work describes the most common electrophoretic methods of performing sample injection for ME applications using electroosmotic flow (EOF), providing both a transition from capillary electrophoresis (CE) separations and a straightforward entry point into ME.


Assuntos
Eletro-Osmose/métodos , Eletroforese em Microchip/métodos , Algoritmos , Injeções
7.
Methods Mol Biol ; 1906: 65-78, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30488385

RESUMO

Electrophoretic on-line sample preconcentration techniques in microfluidic channels improve the sensitivity prior to the separation. Among various techniques, the most important field-amplified sample stacking and sweeping on cross-channel microchips are demonstrated. As a novel microfluidic preconcentration approach, a large-volume sample stacking with electroosmotic flow pump (LVSEP) on straight-channel chips is also presented, which can omit a complicated voltage program for sample injection processes. In this chapter, we describe how to prepare and how to run these on-line sample preconcentration methods in microchip electrophoresis.


Assuntos
Eletro-Osmose/instrumentação , Eletroforese em Microchip/métodos , Tampões (Química) , Calibragem , Eletro-Osmose/métodos , Eletroforese em Microchip/instrumentação , Limite de Detecção , Técnicas Analíticas Microfluídicas/instrumentação , Técnicas Analíticas Microfluídicas/métodos
8.
Electrophoresis ; 40(6): 979-992, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30256428

RESUMO

Induced-charge electroosmosis (ICEO) has attracted tremendous popularity for driving fluid motion from the microfluidic community since the last decade, while less attention has been paid to ICEO-based nanoparticle manipulation. We propose herein a unique concept of hybrid electroosmotic kinetics (HEK) in terms of bi-phase ICEO (BICEO) actuated in a four-terminal spiral electrode array, for effective electrokinetic enrichment of fluorescent polystyrene nanoparticles on ideally polarizable metal strips. First, by alternating the applied AC voltage waves between consecutive discrete terminals, the flow stagnation lines where the sample nanoparticles aggregate can be switched in time between two different distribution modes. Second, we innovatively introduce the idea of AC field-effect flow control on BICEO; by altering the combination of gating voltage sequence, not only the number of circulative particle trapping lines is doubled, but the collecting locations can be flexibly reconfigured as well. Third, hydrodynamic streaming of DC-biased BICEO is tested in our device design, wherein the global linear electroosmosis dominates BICEO contributed from both AC and DC components, resulting in a reduction of particle enrichment area, while with a sharp increase in sample transport speed inside the bulk phase. The flow field associated with HEK is predicted using a linear asymptotic analysis under Debye-Huckel limit, with the simulation results in qualitative agreement with in-lab observations of nanoparticle trapping by exploiting a series of improved ICEO techniques. This work provides an affordable and field-deployable platform for real-time nanoparticle trapping in the context of dilute electrolyte.


Assuntos
Eletro-Osmose/instrumentação , Técnicas Analíticas Microfluídicas/instrumentação , Nanopartículas/química , Eletricidade , Eletro-Osmose/métodos , Desenho de Equipamento , Cinética , Microeletrodos
9.
Anticancer Res ; 38(10): 5733-5738, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30275194

RESUMO

BACKGROUND/AIM: Breast cancer has shown improved prognosis over the years, yet due to different types of breast cancer and different phenotypes of breast cancer cells, it is essential to have an accurate diagnostic procedure. MATERIALS AND METHODS: A unique methodology employing direct current (DC) electrophoresis and electroosmosis in fabricated microfluidic devices was used. This phenomenon was used to discern breast cancer cells from normal breast epithelial cells based on their electrophoretic mobility and electroosmosis. RESULTS: Breast cancer cells (MDA-MB-231) rapidly covered the wound in scratch assay compared to mammary epithelial cells (MCF-10A). However, under DC electrophoresis and electroosmosis MCF-10A cells were observed to move at higher velocities compared to MDA-MB-231 cells under similar voltages. CONCLUSION: Our study provides an economical and efficient method of studying electrophoretic and electrokinetic phenomenon of different cell types that can be used to the advantage of detecting and monitoring cancer progression.


Assuntos
Neoplasias da Mama/patologia , Mama/citologia , Movimento Celular , Eletro-Osmose/métodos , Eletroforese/métodos , Técnicas Analíticas Microfluídicas/métodos , Mama/fisiologia , Proliferação de Células , Células Cultivadas , Feminino , Humanos
10.
ACS Sens ; 3(11): 2320-2326, 2018 11 26.
Artigo em Inglês | MEDLINE | ID: mdl-30350951

RESUMO

In this work, we study transport-induced-charge electroosmosis toward alternating current resistive pulse sensing for the next generation of biomedical applications. Transport-induced-charge electroosmosis, being a new class of electrokinetic phenomenon, occurs as a salt concentration gradient works in synergy with an electric field in ultrathin nanopores. Apart from the conventional electric double layer-governed electroosmotic flow in which the flow behavior is subject to the surface charge, it is found that the transport-induced-charge electroosmotic flow behaves independently of surface charge magnitude but can be linearly regulated by the bulk salt concentration bias. The reversal of the electric field simultaneously inverses the induced charge allowing the establishment of a unidirectional flow under the application of a periodic alternating current field. This unique phenomenon permits continuous water and nanoparticles pumping through a two-dimensional material nanopore in spite of the reversal of the electric field. Built upon this mechanism, we propose a theoretical prototype of alternating current resistive pulse sensing in a two-dimensional nanopore system.


Assuntos
Eletricidade , Eletro-Osmose , Modelos Químicos , Eletro-Osmose/métodos , Nanopartículas/química , Nanoporos , Sais/química , Água/química
11.
J Environ Sci (China) ; 74: 147-158, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30340668

RESUMO

In this study, a magnetic micro-particle conditioning-pressurized vertical electro-osmotic dewatering (MPEOD) process with magnetic micro-particle conditioning-drainage under gravity-mechanical compression-electrical compression (MMPC-DG-MC-EC) stages was established to study the distribution and migration of water, extracellular polymeric substances (EPS), and other organic matter in the activated sludge (AS) matrix at each stage. Results showed that the MPEOD process could attain 53.52% water content (WC) in dewatered AS with bound water (BW) and free water (FW) reduction rates of 82.97% and 99.67%, respectively. The coagulation and time-delayed magnetic field effects of magnetic micro-particles (MMPs) along the MMPC-DG-MC stages initiated the transformation of partial BW to FW in AS. EC had a coupling driving effect of electro-osmosis and pressure on BW, and the changes in pH and temperature at EC stage induced the aggregation of AS flocs and the release of partial BW. Additionally, MMPs dosing further improved the dewatering performance of AS by acting as skeleton builders to provide water passages. Meanwhile, MMPs could disintegrate sludge cells and EPS fractions, thereby reducing tryptophan-like protein and byproduct-like material concentrations in LB-EPS as well as protein/polysaccharide ratio in AS matrix, which could improve AS filterability. At EC stage, the former four Ex/Em regions of fluorescence regional integration analysis for EPS were obviously reduced, especially the protein-like substances in LB- and TB-EPS, which contributed to improvement of AS dewaterability.


Assuntos
Eletro-Osmose/métodos , Fenômenos Magnéticos , Microesferas , Compostos Orgânicos/química , Pressão , Esgotos/química , Água/química
12.
Electrophoresis ; 39(17): 2181-2187, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-29896779

RESUMO

A nanoporous poly-(styrene sulfonate) (poly-SS) membrane was developed for fast and selective ion transport in a microfluidic chip. The poly-SS membrane can be photopolymerized in-situ at arbitrary location of a microchannel, enabling integrated fluidics design in the microfluidic chip. The membrane is characterized by a low hydraulic resistance and a high surface charge to maximize the electroosmotic flow and charge selectivity. The membrane characteristics were investigated by charge-selective electropreconcentration method. Experimental results show membranes with various percentages of poly-SS are able to concentrate anions (fluorescein and TRITC-labeled BSA). The anion-selective electropreconcentration process is stable and 26-times faster than previously reported poly-AMPS (2-acrylamido-2-methyl-1-propanesulfonic acid) based system. The electropreconcentration was also demonstrated to depend on the sample valency and buffer concentration.


Assuntos
Eletro-Osmose/métodos , Membranas Artificiais , Técnicas Analíticas Microfluídicas/métodos , Nanoporos , Ânions/análise , Ânions/química , Ânions/isolamento & purificação , Eletro-Osmose/instrumentação , Desenho de Equipamento , Técnicas Analíticas Microfluídicas/instrumentação , Poliestirenos/química
13.
Eur J Pharm Biopharm ; 127: 204-212, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29477356

RESUMO

Effective treatment of Parkinson's disease (PD) involves administration of therapeutic agents with complementary mechanisms of action in order to replenish, sustain or substitute endogenous dopamine. The objective of this study was to investigate anodal co-iontophoresis of pramipexole (PRAM; dopamine agonist) and rasagiline (RAS; MAO-B inhibitor) in vitro and in vivo. Passive permeation of PRAM and RAS (20 mM each) across porcine skin after 6 h was 15.7 ±â€¯1.9 and 16.0 ±â€¯2.9 µg/cm2, respectively. Co-iontophoresis at 0.15, 0.3 and 0.5 mA/cm2 resulted in statistically significant increases in delivery of PRAM and RAS; at 0.5 mA/cm2, cumulative permeation of PRAM and RAS was 613.5 ±â€¯114.6 and 441.1 ±â€¯169.2 µg/cm2, respectively - corresponding to 38- and 27-fold increases over passive diffusion. Electromigration was the dominant mechanism for both molecules (>80%) and there was no effect on convective solvent flow. Statistically equivalent delivery was observed with human skin. The co-iontophoretic system showed high delivery efficiency with 29% and 35% of the applied amounts of PRAM and RAS being delivered. Preliminary pharmacokinetics studies in rats confirmed that the input rate in vivo was such that therapeutic amounts of the two drugs could be co-administered to humans by transdermal iontophoresis using reasonably sized patches and moderate current densities.


Assuntos
Benzotiazóis/administração & dosagem , Indanos/administração & dosagem , Doença de Parkinson/tratamento farmacológico , Pele/metabolismo , Administração Cutânea , Animais , Química Farmacêutica/métodos , Eletro-Osmose/métodos , Humanos , Iontoforese/métodos , Masculino , Permeabilidade/efeitos dos fármacos , Polimedicação , Pramipexol , Ratos , Ratos Wistar , Absorção Cutânea/efeitos dos fármacos , Suínos
14.
Bioelectrochemistry ; 120: 76-82, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29182911

RESUMO

Employing electric phenomena for the spatial manipulation of bioparticles from whole cells down to dissolved molecules has become a useful tool in biotechnology and analytics. AC electrokinetic effects like dielectrophoresis and AC electroosmosis are increasingly used to concentrate, separate and immobilize DNA and proteins. With the advance of photolithographical micro- and nanofabrication methods, novel or improved bioanalytical applications benefit from concentrating analytes, signal enhancement and locally controlled immobilization by AC electrokinetic effects. In this review of AC electrokinetics of proteins, the respective studies are classified according to their different electrode geometries: individual electrode pairs, interdigitated electrodes, quadrupole electrodes, and 3D configurations of electrode arrays. Known advantages and disadvantages of each layout are discussed.


Assuntos
Eletro-Osmose/instrumentação , Eletroforese/instrumentação , Proteínas/análise , Animais , Eletricidade , Eletrodos , Eletro-Osmose/métodos , Eletroforese/métodos , Desenho de Equipamento , Humanos
15.
ACS Chem Neurosci ; 9(3): 535-544, 2018 03 21.
Artigo em Inglês | MEDLINE | ID: mdl-29078045

RESUMO

It has been known for over a century that the hippocampus, the center for learning and memory in the brain, is selectively vulnerable to ischemic damage, with the CA1 being more vulnerable than the CA3. It is also known that leucine enkephalin, or YGGFL, is neuroprotective. We hypothesized that the extracellular hydrolysis of YGGFL may be greater in the CA1 than the CA3, which would lead to the observed difference in susceptibility to ischemia. In rat organotypic hippocampal slice cultures, we estimated the Michaelis constant and the maximum velocity for membrane-bound aminopeptidase activity in the CA1 and CA3 regions. Using electroosmotic push-pull perfusion and offline capillary liquid chromatography, we inferred enzyme activity based on the production rate of GGFL, a natural and inactive product of the enzymatic hydrolysis of YGGFL. We found nearly 3-fold higher aminopeptidase activity in the CA1 than the CA3. The aminopeptidase inhibitor bestatin significantly reduced hydrolysis of YGGFL in both regions by increasing apparent Km. Based on propidium iodide cell death measurements 24 h after oxygen-glucose deprivation, we demonstrate that inhibition of aminopeptidase activity using bestatin selectively protected CA1 against delayed cell death due to oxygen-glucose deprivation and that this neuroprotection occurs through enkephalin-dependent pathways.


Assuntos
Aminopeptidases/farmacocinética , Região CA1 Hipocampal/metabolismo , Glucose/metabolismo , Fármacos Neuroprotetores/farmacologia , Oxigênio/metabolismo , Animais , Eletro-Osmose/métodos , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Hidrólise/efeitos dos fármacos , Ratos
16.
Electrophoresis ; 39(5-6): 862-868, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-28834563

RESUMO

Nanocoding, a genome analysis platform, relies on very low ionic strength conditions to elongate DNA molecules up to 1.06 (fully stretched DNA = 1). Understanding how electroosmotic and electrophoretic forces vary, as ionic strength decreases, will enable better Nanocoding devices, or other genome analysis platforms, to be developed. Using gel electrophoresis to determine overall mobility (includes contributions from electrophoretic and electroosmotic forces) in different ionic strength conditions, linear DNA molecules (pUC19 (2.7 kb), pBR322 (4.4 kb), ΦX174 (5.4 kb), and PSNAPf-H2B (6.2 kb)) were analyzed in varying gel concentrations (1.50, 1.25, 1.00, 0.75, and 0.50%). Additionally, buffer concentration (Tris-EDTA, TE) was varied to determine free solution mobility at different ionic strength solutions. As ionic strength decreased from 13.8 to 7.3 mM, overall mobility increased. As TE buffer decreased (< 7.3 mM), overall mobility drastically decreased as ionic strength decreased. Rhodamine B dye was utilized to determine the electroosmotic mobility. As the ionic strength decreased, electroosmotic mobility increased. The experimental electrophoretic mobility was compared to theoretical considerations for electrophoretic mobility (Pitts and Debye-Hückel-Onsager). Electroosmotic forces decreased the overall mobility of DNA molecules and bromophenol blue migration in a gel matrix as ionic strength decreased.


Assuntos
DNA/química , Eletro-Osmose/métodos , Eletroforese em Gel de Ágar/métodos , Corantes Fluorescentes/química , Tampões (Química) , Campos Eletromagnéticos , Desenho de Equipamento , Modelos Químicos , Movimento (Física) , Concentração Osmolar , Rodaminas/química
17.
Electrophoresis ; 39(5-6): 760-769, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29115696

RESUMO

The use of an electric field in free-flow zone electrophoresis (FFZE) automatically leads to Joule heating yielding a higher temperature at the center of the separation chamber relative to that around the channel walls. For small amounts of heat generated, this thermal effect introduces a variation in the equilibrium position of the analyte molecules due to the dependence of liquid viscosity and analyte diffusivity on temperature leading to a modification in the position of the analyte stream as well as the zone width. In this article, an analytic theory is presented to quantitate such effects of Joule heating on FFZE assays in the limit of small temperature differentials across the channel gap yielding a closed form expression for the stream position and zone variance under equilibrium conditions. A method-of-moments approach is employed to develop this analytic theory, which is further validated with numerical solutions of the governing equations. Interestingly, the noted analyses predict that Joule heating can drift the location of the analyte stream either way of its equilibrium position realized in the absence of any temperature rise in the system, and also tends to reduce zone dispersion. The extent of these modifications, however, is governed by the electric field induced temperature rise and three Péclet numbers evaluated based on the axial pressure-driven flow, transverse electroosmotic and electrophoretic solute velocities in the separation chamber. Monte Carlo simulations of the FFZE system further establish a time and a length scale over which the results from the analytic theory are valid.


Assuntos
Eletroforese/métodos , Temperatura Alta , Vapor , Difusão , Eletro-Osmose/métodos , Hidrodinâmica , Modelos Teóricos , Método de Monte Carlo , Fenômenos Físicos , Pressão , Viscosidade
18.
Anal Chem ; 89(20): 10806-10812, 2017 10 17.
Artigo em Inglês | MEDLINE | ID: mdl-28944662

RESUMO

Single-cell analysis has attracted increasing attention because of cell heterogeneities. Various strategies have been developed for analyzing single cells, but most of these analytical processes kill the cells. Tools that can qualitatively and quantitatively measure the cellular contents without killing the cell are highly demanding because they enable us to conduct single-cell time-course studies (e.g., to examine how a cell responds to a therapy before, during, and after a treatment). Here we develop a femto-liter (fL) pipet to serve this purpose. To ensure that we can accurately and precisely pipet fL solutions, we fill all conduits with liquid and use an electroosmotic pump (EOP) as the driving force to facilitate withdrawal of cellular contents from single cells. We tentatively term this device an EOP-driven pipette or EDP. We characterize the EDP for accurately and precisely withdrawing solution from ∼250 fL to 80 nL; a volume range that covers the applications for most types of cells. To demonstrate the feasibility of utilizing the EDP for a single-cell time-course study, we utilize the EDP to take the cellular contents out at different times during the course of a zebrafish embryo development for cholesterol measurements. More than 50% of the embryos survive after each pipetting and analysis step, and this number will increase considerably as we improve our cell manipulation skills and reduce the pipet-tip diameter. We expect this EDP to become an effective tool for single-cell time-course studies.


Assuntos
Colesterol/análise , Eletro-Osmose/métodos , Embrião não Mamífero/metabolismo , Animais , Eletro-Osmose/instrumentação , Análise de Célula Única , Peixe-Zebra
19.
Electrophoresis ; 38(24): 3130-3135, 2017 12.
Artigo em Inglês | MEDLINE | ID: mdl-28869669

RESUMO

The measurement of electroosmotic flow (EOF) is important in a capillary electrophoresis (CE) experiment in terms of performance optimization and stability improvement. Although several methods exist, there are demanding needs to accurately characterize ultra-low electroosmotic flow rates (EOF rates), such as in coated capillaries used in protein separations. In this work, a new method, called the two-step method, was developed to accurately and rapidly measure EOF rates in a capillary, especially for measuring the ultra-low EOF rates in coated capillaries. In this two-step method, the EOF rates were calculated by measuring the migration time difference of a neutral marker in two consecutive experiments, in which a pressure driven was introduced to accelerate the migration and the DC voltage was reversed to switch the EOF direction. Uncoated capillaries were first characterized by both this two-step method and a conventional method to confirm the validity of this new method. Then this new method was applied in the study of coated capillaries. Results show that this new method is not only fast in speed, but also better in accuracy.


Assuntos
Eletro-Osmose/métodos , Eletroforese Capilar/métodos , Reprodutibilidade dos Testes
20.
Electrophoresis ; 38(20): 2576-2586, 2017 10.
Artigo em Inglês | MEDLINE | ID: mdl-28763135

RESUMO

Insulator-based dielectrophoresis (iDEP) has emerged as a powerful tool for multiple biomicrofluidic operations, such as cell separation and concentration. The key feature for iDEP systems is the alteration of insulating microchannel geometries to create strong electric field gradients. Under AC electric fields, this strong electric field gradient can affect fluid flow by (at least) two nonlinear electrokinetic phenomena; (a) electrothermal flow due to Joule heating and (b) induced charge electroosmosis (ICEO) near the microchannel constrictions of small (but finite) permittivity and conductivity. This paper presents an experimental and theoretical study on the interplay of electrothermal and ICEO flows near microchannel constrictions with various geometries and fluid ionic strengths, which are crucial design factors for iDEP systems. Temperature rise and fluid velocities in 2D Gaussian-shaped constrictions were studied experimentally with supporting analytical estimations and numerical simulations. Additionally, we show qualitatively distinct recirculating flow patterns in 2D and 3D microchannel constrictions used for iDEP systems. Approximate analytical expressions for electrothermal and ICEO velocity scales are provided as a function of constriction geometry, bulk electrolyte concentration, and the applied electric field. Insights from this study will be useful in designing microfluidic systems for electrokinetic particle manipulation.


Assuntos
Eletro-Osmose/métodos , Eletroforese/instrumentação , Técnicas Analíticas Microfluídicas/métodos , Simulação por Computador , Eletricidade , Cinética , Reologia , Temperatura , Termodinâmica
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