Effect Of Electroosmotic Flow Research Articles

Single-Molecule Identification and Quantification of Steviol Glycosides with a Deep Learning-Powered Nanopore Sensor.

Steviol glycosides (SGs) are a class of high-potency noncalorie natural sweeteners made up of a common diterpenoid core and varying glycans. Thus, the diversity of glycans in composition, linkage, and isomerism results in the tremendous structural complexity of the SG family, which poses challenges for the precise identification and leads to the fact that SGs are frequently used in mixtures and their variances in biological activity remain largely unexplored. Here we show that a wild-type aerolysin nanopore can detect and discriminate diverse SG species through the modulable electro-osmotic flow effect at varied applied voltages. At low voltages, the neutral SG molecule was drawn and stuck in the pore entrance due to an energy barrier around R220 sites. The ensuing binding events enable the identification of the majority of SG species. Increasing the voltage can break the barrier and cause translocation events, allowing for the unambiguous identification of several pairs of SGs differing by only one hydroxyl group through recognition accumulation from multiple sensing regions and sites. Based on nanopore data of 15 SGs, a deep learning-based artificial intelligence (AI) model was created to process the individual blockage events, achieving the rapid, automated, and precise single-molecule identification and quantification of SGs in real samples. This work highlights the value of nanopore sensing for precise structural analysis of complex glycans-containing glycosides, as well as the potential for sensitive and rapid quality assurance analysis of glycoside products with the use of AI.

Investigating of electro-osmotic flow effects due to electrical stimulation therapy using computational fluid dynamics

Investigating of electro-osmotic flow effects due to electrical stimulation therapy using computational fluid dynamics

Numerical study of rectified electroosmotic flow in nanofluidics: Influence of surface charge and geometrical asymmetry

The transport of ions in nanofluidic systems, specifically the rectified ion transport or the ionic diode phenomenon occurring in the presence of asymmetrical geometry and/or charge distribution, has drawn considerable attention due to its relevance in energy conversion and biosensing applications. However, previous numerical research has frequently overlooked the concurrent liquid flow within these systems, even though multiple experimental studies have highlighted intriguing flow patterns in ionic diode configurations. In the present study, we employ comprehensive numerical simulations to probe the influence of geometrical or charge asymmetry in a nanofluidic system on electroosmotic flow and ion transport. These simulations employ the Poisson–Nernst–Planck equation in conjunction with the Navier–Stokes equation. Our findings reveal that even when the current rectification trend is consistent between conical and straight nanopores, charge asymmetry and geometric asymmetry can generate significant variations in the rectification effects of electroosmotic flow. Furthermore, our research indicates that the direction of ion rectification and flow rectification can be independently manipulated by utilizing charge asymmetry in conjunction with geometric asymmetry, thereby facilitating advanced control of ions and flows within nanofluidic systems. Collectively, our findings contribute to a more profound understanding of the mechanisms underlying osmotic flow rectification and propose a novel approach for developing efficient ion and flow rectification systems.

Performance enhancement of electrodialysis regeneration of deep eutectic solvent for liquid desiccant air conditioning systems

Despite the promising energy-saving potential of the electrodialysis regeneration technique for liquid desiccant regeneration in air conditioning systems, there are still issues that need to be resolved in electrodialysis separation systems, such as the high initial cost owing to the complexity of the cell gaps, over-limiting current, and electro-osmotic flow effects. This study utilized stereolithography (SLA) 3-D printing technology to manufacture a low-cost scalable model of an electrodialysis system. An electrodialysis system with a cell gap of 5 mm and serpentine flow feed spacers was investigated to regenerate deep eutectic solvent (DES) developed from choline chloride and ethylene glycol as a bio-friendly liquid desiccant for air conditioning systems. Ammonium chloride electrode rinsing solution with about 250 mS/cm electric conductivity was utilized to enhance the conductive properties of the system. The optimum parametric operating conditions for the system are found to be around 0.0058 m/s for the circulation flow rate, 0–4 wt.% for the concentration difference of the diluted and regenerated solutions' cells, and 6–8 V voltage supply energy input. In 60 minutes of operation, the current efficiency value of the constructed model was discovered to be as high as 65.82%. Matching the performance threshold of the commercial electrodialysis equipment described in the literature for regenerating lithium chloride conventional liquid desiccant.

Investigation of entrance effects on particle electrophoretic behavior near a nanopore for resistive pulse sensing.

Resistive pulse sensing using solid-state nanopores provides a unique platform for detecting the structure and concentration of molecules of different types of analytes in an electrolyte solution. The capture of an entity into a nanopore is subject not only to the electrostatic force but also the effect of electroosmotic flow originating from the charged nanopore surface. In this study, we theoretically analyze spherical particle electrophoretic behavior near the entrance of a charged nanopore. By investigating the effects of pore size, particle-pore distance, and salt concentration on particle velocity, we summarize dominant mechanisms governing particle behavior for a range of conditions. In the literature, the Helmholtz-Smoluchowski equation is often adopted to evaluate particle translocation by considering the zeta potential difference between the particle and nanopore surfaces. We point out that, due to the difference of the electric field inside and outside the nanopore and the influence from the existence of the particle itself, the zeta potential of the particle, however, needs to be at least 30% higher than that of the nanopore to allow the particle to enter into the nanopore when its velocity is close to zero. Accordingly, we summarize the effective salt concentrations that enable successful particle capture and detection for different pore sizes, offering direct guidance for nanopore applications.

Space charge modulation and ion current rectification of a cylindrical nanopore functionalized with polyelectrolyte brushes subject to an applied pH-gradient

Considering versatile potential applications of bioinspired membranes, we simulate the electrokinetic behavior of a cylindrical nanopore, surface modified by a polyelectrolyte (PE) layer. Taking account of the effect of electroosmotic flow and an additionally applied pH gradient, the influences of the strength of the pH gradient, the PE layer thickness, the length of the nanopore and its radius on its conductance and ion current rectification (ICR) performance are assessed. We show that if pHU (the pH at the higher pH end of the nanopore) is fixed at 11 and pHL (the pH at the lower pH end of the nanopore) varies from 3 to 11, the rectification factor Rf has a local maximum occurring in 6 < pHL <8; the greater the magnitude of the applied potential bias |V| the smaller the pHL at which the local maximum occurs. The influence of the PE layer thickness on the nanopore rectification performance is important only if 5 < pHL <8, and the optimum performance is reached at a medium thick PE layer (ca. 3 nm). Possible mechanisms associated with the ion transport phenomenon under consideration are proposed and discussed in detail.

Modeling and Simulations of Buongiorno's Model for Nanofluid in a Microchannel with Electro-Osmotic Effects and an Exothermal Chemical Reaction.

The article presents a mathematical model for the magnetized nanofluid flow and heat transfer with an exothermic chemical reaction controlled by Arrhenius kinetics. Buongiorno’s model with passive boundary condition is employed to formulate the governing equation for nanoparticles concentration. The momentum equation with slip boundary conditions is modelled with the inclusion of electroosmotic effects which remain inattentive in the study of microchannel flows with electric double layer (EDL) effects. Conclusions are based on graphical and numerical results for the dimensionless numbers representing the features of heat transfer and fluid flow. Frank-Kamenetskii parameter resulting from the chemical reaction showed significant effects on the optimization of heat transfer, leading to increased heat exchangers’ effectiveness. The Hartmann number and slip parameter significantly affect skin friction, demonstrating the notable effects of electroosmotic flow and the exothermic chemical reaction on heat transfer in microchannels. This analysis contributes to prognosticating the convective heat transfer of nanofluids on a micro-scale for accomplishing successful thermal designs.

The polarization reverse of diode-like conical nanopore under pH gradient

In the past decade, with the improvement of nanofabrication technology, silica nanopores and nanochannels have been widely used in the fields of ion pumps, energy conversion, ion channels, metal ion detection, and biosensors. Although both potential and pH gradient can significantly change the performance of ion current rectification in nanoscale, the potential mechanism is still not fully understood. In this study, the ion current rectification, surface charge distribution and ion selectivity of silica nanopore under different background salt concentration and pH gradient were discussed by an analytical model, which takes into account the effects of electroosmotic flow, multiple ionic species, and the acid base neutralization. The results show that the polarity of nanopore rectifier can be changed by changing the acidity and alkalinity at both ends of the nanopore. For the first time, we find that the rectification polarity of silica conical nanopore exhibits different performances under high and low electric field intensity. One case in this study shows the rectification ratio curve of the nanopore will have a maximum or minimum value and the extreme point is near the zero of the ion current. With the increase of the concentration of background salt solution, the voltage at the zero point of ion current approaches the zero point, and then the maximum or minimum point moves to the left. The extreme point offset and polarity reversal phenomena may have potential application value in nanopore-based sensing devices.

Application of poly(2-methyl-2-oxazoline) in protein separation by capillary electrophoresis

Capillary electrophoresis (CE), a commonly used liquid-phase separation technology, has many advantages such as high analysis speed, high separation efficiency, and low sample consumption. Hence, CE has gained popularity in food analysis, medical clinical diagnosis, environmental monitoring, and biological sample separation, especially in the field of protein separation and analysis. However, the fused silica capillaries that are commonly used in CE easily adsorb proteins, resulting in unstable electroosmotic flow and poor reproducibility of the separation results. In addition, due to the short optical path of the typical ultraviolet detectors employed in commercial CE, the detection sensitivity often does not meet the requirements for the direct analysis of low-abundance proteins. Therefore, developing a coating that can prevent protein adsorption and improve detection sensitivity is one of the important challenges in CE separation and analysis of proteins. Poly(2-methyl-2-oxazoline), a peptide-like hydrophilic polymer, not only has hydrophilicity, protein-repellent ability, and biocompatibility similar to the gold standard of the anti-protein adsorption polymer (polyethylene glycol), but also shows better stability than polyethylene glycol due to its peptide-like structure. Therefore, it has been increasingly used in biomass transfer, drug carrier, and impedance protein adsorption in recent years. This article aims to review the recent applications of poly(2-methyl-2-oxazoline) in CE from two standpoints. First, poly(2-methyl-2-oxazoline) was grafted onto the capillary inner wall using polydopamine as an anchor. The resulting coated capillary successfully separated a mixture of proteins (such as lysozyme, cytochrome C, ribonuclease A, and α -pancreas chymosinogen A), in addition to preventing the non-specific adsorption of other proteins during the quantitative analysis of melamine and lactoferrin in milk powder. Thus, the detection efficiency of melamine and lactoferrin in milk powder was improved. Second, poly(2-methyl-2-oxazoline) was used to produce a binary mixed brush coating with a stimulus-responsive polymer (such as polyacrylic acid). The capillary coated with the mixed brushes could adsorb high amounts of the target protein (such as bovine serum albumin and lysozyme) under certain pH and ionic strength conditions, and most of the adsorbed proteins could be desorbed by changing the pH and ionic strength. During the release, poly(2-methyl-2-oxazoline) present on the coating would prevent the adsorption of proteins. Under the dual effects of electroosmotic flow and electrophoresis, the released protein could migrate rapidly, and the instantaneous concentration of the protein reaching the detector could be greatly increased. Therefore, the target proteins could be on-line concentrated and the detection signals could be amplified, resulting in improved detection sensitivity for the protein. Future development trends in the function of poly(2-methyl-2-oxazoline) for the separation of proteins by CE are also discussed.

Reduced-order modelling of concentration polarization with varying permeation: Analysis of electro-osmosis in membranes

Concentration polarization is a major challenge to water desalination process. It affects membrane performances by reducing permeate flux and increasing the risk of fouling. One promising approach to reduce concentration polarization is to use external forces such as electro-osmosis. Previously developed reduced-order model either assumed dissolving wall condition, which does not represent the real process mechanism or does not incorporate the effect of electro-osmotic flow (EOF) slip velocity. In this work, we bridge the research gap by proposing a reduced-order model with permeation for membrane systems by considering the effect of EOF slip velocity. The proposed model is shown to provide accurate prediction when compared with computational fluid dynamics (CFD) results. Additionally, the model can complete simulations in seconds, which is 2 orders of magnitude faster as compared to CFD. Using the validated model, we study the mechanism of mixing caused by the slip velocity. Results show that improved mixing and enhanced mass transfer is concentrated in the region between electrodes. We also propose analytical expressions to determine shear stress and pressure drop, which are linked to mass transfer enhancement and energy requirement respectively. This leads us to obtain an optimal electrode spacing to improve mass transfer.

CHARACTERIZATION OF INTERACTION BETWEEN BUDDLEOSIDE AND BOVINE SERUM ALBUMIN

The primary objective of this study was to investigate the binding of buddleoside to bovine serum albumin (BSA) by different analytical techniques. The analytical principles of affinity capillary electrophoresis (ACE) and fluorescence spectroscopy used in the experiments were different. Mobility (M) that is independent of viscosity of the operating buffer and voltage was chosen to eliminate the effects of electroosmotic flow (EOF) in ACE and was applied to estimate the binding constant Ka. The quenching constant Ksv, binding site number n and binding constant Kb were provided by the fluorescence quenching method. After data analysis of the fluorescence quenching process, it can be seen that the quenching of BSA by buddleoside is a static quenching method. The binding constants between buddleoside and BSA obtained from ACE and fluorescence spectra were 1.218×105 and 1.1915×105, respectively. According to the thermodynamic parameters of ΔG, ΔH and ΔS, it can be inferred that Van Der Waals force and hydrogen bonding force exist in the interaction between buddleoside and BSA. This study can provide a reference for the study of the transport and function mechanism of buddleoside in vivo.

Regulating the ionic current rectification behavior of branched nanochannels by filling polyelectrolytes

The overlapping of the electric double layer (EDL) in a nanochannel yields many interesting and significant electrokinetic phenomena such as ionic current rectification (ICR), which occurs only at a relatively low bulk salt concentration (∼1 mM) where the EDL thickness is comparable to the nanochannel size. In an attempt to raise this concentration to higher levels and the ICR performance improved appreciably, a branched nanochannel filled with polyelectrolytes (PEs) is proposed in this study. We show that these objectives can be achieved by choosing appropriate PE. For example, if the stem side of an anodic aluminun oxide nanochannel is filled with polystyrene sulfonate (PSS) an ICR ratio up to 850 can be obtained at 1 mM, which was not reported in previous studies. Taking account of the effect of electroosmotic flow, the underlying mechanisms of the ICR phenomena observed are discussed and the influences of the solution pH, the bulk salt concentration, and how the region(s) of a nanochannel is filled with PE examined. We show that the ICR behavior of a branched nanochannel can be modulated satisfactorily by filling highly charged PE and the solution pH.

Discrimination of Protein Amino Acid or Its Protonated State at Single-Residue Resolution by Graphene Nanopores.

The function of a protein is determined by the composition of amino acids and is essential to proteomics. However, protein sequencing remains challenging due to the protein's irregular charge state and its high-order structure. Here, a proof of principle study on the capability of protein sequencing by graphene nanopores integrated with atomic force microscopy is performed using molecular dynamics simulations. It is found that nanopores can discriminate a protein sequence and even its protonation state at single-residue resolution. Both the pulling forces and current blockades induced by the permeation of protein residues are found to be highly correlated with the type of amino acids, which makes the residues identifiable. It is also found that aside from the dimension, both the conformation and charge state of the residue can significantly influence the force and current signal during its permeation through the nanopore. In particular, due to the electro-osmotic flow effect, the blockade current for the double-protonated histidine is slightly smaller than that for single-protonated histidine, which makes it possible for discrimination of different protonation states of amino acids. The results reported here present a novel protein sequencing scheme using graphene nanopores combined with nanomanipulation technology.

Influence of temperature and electroosmotic flow on the rectification behavior of conical nanochannels

Abstract Considering various potential applications of charged nanochannels, we studied theoretically the electric field driven ion transport in a conical nanochannel connecting two large, identical reservoirs filled with an aqueous KCl solution. Taking account of the effect of electroosmotic flow (EOF), the associated electrokinetic behaviors under various conditions are examined, focusing on the influences of the temperature and the bulk salt concentration on the degree of ionic current rectification (ICR) and the conductance. Assuming that the bulk salt concentration ranges from 1 to 1000 mM and temperature from 278 to 313 K, we show that neglecting the EOF effect will either underestimate or overestimate the ionic current, and can lead to ca. 90% deviation in the degree of ICR. In general, the higher the temperature the greater the conductance and the less significant the ICR effect, and the degree of this effect has a local maximum as the bulk salt concentration varies. A three dimensional plot correlating the ICR effect with the bulk salt concentration and the temperature is prepared for the design of the nanochannel-based thermal gates for ionic transport.

Electrically-responsive deformation of polyelectrolyte complex (PEC) fibrous membrane

This study aims at the effect of electro-osmotic flow on a fibrous membrane comprised of assembled oppositely-charged polyelectrolytes and submerged in aqueous ionic solution. As electric field is applied across an edge-clamped circular membrane, it deforms under the action of a transverse force, the origin of which is in focus. Fibers were electrospun from a blend of poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA). A model is presented, which explains and describes the membrane deformation in terms of the ionic strength and pH level of the solution, the membrane geometry and porosity, the ζ-potential and elastic modulus of the membrane, as well as the applied cross-membrane electric potential difference. The model is corroborated by a set of experiments. The dependence of the membrane deformation on the electric potential was found to be rather weak, while the elastic modulus was found to be strongly dependent on the solution pH.

Effect of Electroosmotic Flow on the Electrophoretic Deposition of Zeolite Powder on a Porous Alumina Support

Using a porous alumina support, seeding for the preparation of a zeolite separation membrane is conducted by placing the electrodes for electrophoretic deposition (EPD) on both sides of the support. In this case, two electrokinetic phenomena are observed: electrophoresis of the seed crystal particles and electroosmotic flow of the solvent within the porous alumina support. When water and acetone are used, the direction of electroosmotic flow is opposite to that of EPD, and the strength of electroosmotic flow with water is higher than that with acetone. In contrast, with methanol, the direction of the electroosmotic flow is the same as that for EPD, with a weak particle charge. The results show that both the support and the solvent contribute to the change in the strength and direction of the electroosmotic flow.

Effect of electroosmotic flow of aqueous suspension of nanosilica on the properties of carbonated concrete

The paper investigates the possibility to use electroosmosis to transport nanosilica (NS) particles inside carbonated concrete, in order to exert a filler effect and enhance its durability performance. This method aims to extending possible beneficial effects of NS to existing reinforced concrete structures, where the presence of a carbonated layer of concrete is very likely. Injection tests were performed with electrochemical cells on carbonated concrete discs with water/cement (w/c) ratios of 0.50, 0.55 and 0.65, using a NS aqueous suspension at the anode. The results indicated that a flow did occur through the concrete disc and it was directed from the anode towards the cathode. A linear relationship between flux and applied voltage gradient was obtained, which is typical of electroosmotic phenomena. The bulk properties of concrete, such as density, water absorption and sorptivity, were not affected by the injection tests, whilst electrical resistivity increased indicating a mild ‘sealing’ effect on the surface. Also microstructural analyses highlighted the local presence of NS that decreased the local porosity close to the surface.

Effect of Electroosmotic Flow on the Transport of α-Cyclodextrin through the Channel CymA

CymA, an outer membrane channel of Klebsiella oxytoca, allows the passive diffusion of the bulky molecule α-cyclodextrin (α-CD, M.W. 972.8 Da) to the periplasm of the bacterium [1]. In single channel electrophysiology experiments, the flow of the uncharged α-CD was found asymmetric with respect to the applied voltage and ionic salts used. The net water current associated with the ion movement, i.e., the so-called electroosmotic flow (EOF), is induced by the ionic selectivity of the pore. This effects has been found to be a major factor behind the modified interactions of the α-CD molecule with the channel [2]. To get atomistic insight into the EOF on α-CD permeation, we have performed ∼40 μs free energy calculations in presence of three different ionic conditions, i.e., in the absence of ions, in the presence of 1 M KCl and of 1 M MgCl2, using well-tempered matadynamics simulations [3] applying an external field of 0 V, +1 V and −1 V. No major changes in the free energy landscapes were observed in the absence of ions at both polarities of the voltage. This finding indicates the absence of an electrophoretic effect on the neutral α-CD molecule and of an EOF mediated effect due to the absence ions. However, using an electric field together 1 M KCl salt, we observed significant free energy changes in the transport of the α-CD consistent with net EOF at both voltage polarities. Moreover, using 1 M MgCl2 salt, we demonstrate an alteration of the pore selectivity from cationic to anionic. Thereby, the direction of the resulting EOF at a particular voltage polarity and its effect on the α-CD permeation is inverted. These results highlight the role of the EOF in the transport of α-CD through the nanometer-sized CymA channel.[1] van den Berg B. et al., Proc. Natl. Acad. Sci. USA 2015, 112, E2991-E2999.[2] Bhamidimarri, S. P. et al., Biophys. J. 2016, 110, 600-611.[3] Barducci, A. et al., Phys. Rev. Lett. 2008, 100, 020603.

Electroosmotic flow in optimally operated micro heat pipes

Micro heat pipe, a capillary-driven two-phase heat transfer microsystem, serves as an effective cooling device for electronic components. Based on a mathematical model employing the conservation laws to yield the heat and fluid flow characteristics of a micro heat pipe, we demonstrate how the basic principles of electroosmotic flow can be applied to enhance the performance of micro heat pipes. To provide a thorough and comprehensive analysis, both favorable and adverse effects of electroosmotic flow on the thermal performance of a micro heat pipe are studied. The thermal performance of a micro heat pipe is strongly dependent on the circulation effectiveness of working fluid. A well-defined parameter is employed to characterize the effects of the electric force on the circulation effectiveness of the working fluid with different ion concentrations. The aiding effect of electric force increases the circulation rate of working fluid, resulting in a significant enhancement in the heat transport capacity of micro heat pipe. By investigating the solid wall temperature profiles, the use of electroosmosis in enhancing the thermal performance of a micro heat pipe is deemed to be practically feasible due to the fact that significant enhancement can be achieved with a compensation of small temperature drop at a reasonably low applied voltage.

Molecular Dynamics Simulation of DNA Capture and Transport in Heated Nanopores.

The integration of local heat sources with solid-state nanopores offers new means for controlling the transmembrane transport of charged biomacromolecules. In the case of electrophoretic transport of DNA, recent experimental studies revealed unexpected temperature dependences of the DNA capture rate, the DNA translocation velocity, and the ionic current blockades produced by the presence of DNA in the nanopore. Here, we report the results of all-atom molecular dynamics simulations that elucidated the effect of temperature on the key microscopic processes governing electric field-driven transport of DNA through nanopores. Mimicking the experimental setup, we simulated the capture and subsequent translocation of short DNA duplexes through a locally heated nanopore at several temperatures and electrolyte conditions. The temperature dependence of ion mobility at the DNA surface was found to cause the dependence of the relative conductance blockades on temperature. To the first order, the effective force on DNA in the nanopore was found to be independent of temperature, despite a considerable reduction of solution viscosity. The temperature dependence of the solution viscosity was found to make DNA translocations faster for a uniformly heated system but not in the case of local heating that does not affect viscosity of solution surrounding the untranslocated part of the molecule. Increasing solution temperature was also found to reduce the lifetime of bonds formed between cations and DNA. Using a flow suppression algorithm, we were able to separate the effects of electro-osmotic flow and direct ion binding, finding the reduced durations of DNA–ion bonds to increase, albeit weakly, the effective force experienced by DNA in an electric field. Unexpectedly, our simulations revealed a considerable temperature dependence of solvent velocity at the DNA surface—slip velocity, an effect that can alter hydrodynamic coupling between the motion of DNA and the surrounding fluid.