Influence Of Electroosmotic Flow Research Articles

Time-periodic electrokinetic analysis of a micropolar fluid flow through hydrophobic microannulus

The oscillating aspects of pressure-driven micropolar fluid flow through a hydrophobic cylindrical microannulus under the influence of electroosmotic flow are analytically studied. The study is based on a linearized Poisson–Boltzmann equation and the micropolar model of Eringen for microstructure fluids. An analytical solution is obtained for the distributions of electroosmotic flow velocity and microrotation as functions of radial distance, periodic time, and relevant parameters. The findings of the present study demonstrate that, unlike the decrease in flow rate resulting from the micropolarity of fluid particles, velocity slip and spin velocity slip, when contrasted with Newtonian fluids, act as a counteractive mechanism that tends to enhance the flow rate. Additionally, the findings indicate that a square plug-like profile in electroosmotic velocity amplitude is observed when the electric oscillating parameter is low and the electrokinetic width is large, for both Newtonian and micropolar fluids. Moreover, in cases where there is a wide gap between the cylindrical walls and a high-frequency parameter, the electroosmotic velocity and microrotation amplitudes tend to approach zero at the center of the microannulus across all ranges of micropolarity and zeta potential parameters. Furthermore, it has been observed that the amplitude of microrotation strength rises as slip and spin slip parameters increase. Across the entire spectrum of micropolarity, the zeta potential ratio influences both the dimension and direction of the electroosmotic velocity profiles within the electric double layer near the two cylindrical walls of the microannulus. The study emphasizes the physical quantities by presenting graphs for various values of the pertinent parameters juxtaposing them with existing data in the literature and comparing them with the Newtonian fluids.Graphic abstract

Extraction and transformation of elements in phosphogypsum by electrokinetics

Phosphogypsum (PG), as a typical industrial solid waste produced in the wet production process of phosphoric acid, is harmful to the environment and difficult to utilize. In order to explore the migration behavior of impurities in PG under electrokinetic treatment and provide a new treatment technology for the purification and harmless treatment, this paper studied the distribution of soluble impurities (PO43−, F−, Sr, Pb, Cr, Cu, and Mn) in PG under different electrokinetic treatment conditions. The results indicated that most of water-soluble impurities demonstrated obvious migration distribution laws at different voltages. Under the influence of electroosmotic flow, F− accumulated continually at the cathode. Positive MF+ was produced in acidic circumstances by combining F− and metal ions and travelled to the cathode under the combined action of electric field force and electroosmotic flow. Under electrokinetic treatment, the concentration of PO43− in the anode chamber increased while that of in the cathode chamber decreased. A large number of anions in PG were attached to the anode by coulomb force, reducing the potential. PO43− was s largely enriched in the anode chamber, which is controlled by the free diffusion effect of ions. Heavy metals exhibited higher leaching efficiency under anodic acid conditions. With the increase of applied voltage, the concentration of heavy metals in the anode chamber gradually increased, which was related to the activity of solution, pH and other factors. The above results indicate that electrokinetic treatment is a novel and efficient PG treatment technology, which has a broad application prospect in impurity removal and PG resource recovery.

A novel micro-nanofluidic preconcentrator with Koch fractal nanochannel surface

With the development of the times, the demand for rapid detection of trace toxic and harmful components and circulating tumor cells is increasing and it is urgent to develop portable specialized detection instruments. Since it is difficult to directly measure the sample material in the trace amount detection, the method of high-enrichment of the trace substance based on the ion concentration polarization principle can make the trace substance easy to be determined. In this paper, a novel micro-nanofuidic preconcentrator with Koch fractal nanochannel surface is proposed. By coupling the Poisson-Nernst-Planck equation and the Navier-Stokes equation, the influence of Koch fractal parameters on ion enrichment was studied by numerical simulation. The results show that increasing the unit length L, increasing fractal time n, using the unstraggered structure and increasing the fractal angle θ can significantly increase the ion enrichment ratio. In addition, we found that the above means can reduce the fluid flow velocity in the nanochannel and thus reduce the negative influence of electroosmotic flow on ion enrichment. This work provides a theoretical basis for the design of trace detection instruments based on micro-nanofluidic platform.

Investigation of binding behavior of important metal ions to thioredoxin reductase using mobility-shift affinity capillary electrophoresis: A preliminary insight into the development of new metal-based anticancer drugs

Thioredoxin reductase (TrxR) is a redox enzyme that is found to be elevated in a variety of tumors and its inhibition has been proved to be a new approach for the treatment of cancer. In this study, the binding behaviors of some metal ions on TrxR have been evaluated using mobility-shift affinity electrophoresis. Eighteen medicinally important metal ions from soft, borderline and hard categories were selected for the screening. This study was based on the fact that, overall mass, charge and size of a protein changes after interaction with charged ligands such as metal ions, which affects the electrophoretic movement of the analyte protein under the influence of electroosmotic flow. This alteration in electrophoretic mobility of the analyte is proportional to the strength of interaction between the two species and is utilized to calculate the binding results. The mobility ratio (R) of an EOF marker (injected in same run) and the analyte enzyme was determined and the binding result was expressed as the normalized difference of the mobility ratios of test enzyme with and without metal ion (ΔR/Rf) and its confidence interval. The method showed excellent precision, as the % RSD of mobility ratios of replicate runs (n = 6) for most of the enzyme-metal ion pair was found to be <1%. Six out of eighteen tested metal ions including Ir3+, Ag+, Os3+, Cr3+, Fe2+ and Rh3+ showed significant binding interactions (ΔR/Rf ≥ ±0.01), while for others, it was found to be weak or insignificant. Among all the tested metal ions, Ir3+ (ΔR/Rf = −0.27065 ± 0.00818) showed the strongest interaction followed by Ag+ (ΔR/Rf = −0.09821 ± 0.00783), Fe2+ (ΔR/Rf = −0.0482 ± 0.00701), Os3+ (ΔR/Rf = −0.04382 ± 0.00751), Cr2+ (ΔR/Rf = −0.04093 ± 0.01206) and Rh3+ (ΔR/Rf = −0.01455 ± 0.00857). The values of ΔR/Rf obtained for most of the enzyme-metal ion pair were negative, suggesting the multifaceted complexation behavior of metal ions, as they get coordinated with surrounding anions after initial binding with the enzyme. As a result, the overall charge on the enzyme becomes more negative. Significant interactions of the enzyme with some metal ions suggested that the drugs based on these metal ions may prove to be potential inhibitor of the enzyme, however, it would be interesting to evaluate that how these interactions would affect the function and stability of the enzyme.

Ionic Current Rectification in a Conical Nanopore: Influences of Electroosmotic Flow and Type of Salt

The influence of electroosmotic flow (EOF) on the behavior of the ionic current rectification (ICR) in a conical nanopore connecting two large identical reservoirs is investigated. In particular, the effect of the type of salt is examined by considering LiCl, NaCl, and KCl. We show that neglecting EOF is capable of influencing ICR both quantitatively and qualitatively. If EOF is neglected, the rectification factor at each level of the applied electric potential bias across the two reservoirs for the case of LiCl (KCl) is always the largest (smallest). However, if EOF is taken into account, the relative magnitude of the rectification factors for various salts depends upon the level of the applied electric potential bias. This behavior is consistent with the experimental observation in the literature and can be explained by the degree of ion enrichment/depletion in a nanopore.

Ionic Current Rectification in a Conical Nanopore: Influence of Salt

Because it is capable of mimicking the ion channels of living organisms, the ionic transport in an artificial nanopore has drawn the attention of many researchers, recently. A considerable amount of efforts has also been made on relevant analyses due to the fast advances in nanotechnology and wide potential applications. As the linear size of a channel is down to the order of Debye length (or thickness of electric double layer), the overlapping of electric double layers yields distinctive electrokinetic phenomena. These include, for example, ion concentration polarization, ion selectivity, and ion current rectification. Ion current rectification is the phenomenon that a nanopore shows a diode-like current-voltage behavior, or the preference for ionic current in a certain direction when an electric potential is applied. For charged nanopores, ion current rectification might arise from several reasons, such as asymmetric pore geometry, imposed salt gradient, and bipolar surface properties. In the present study, the influence of electroosmotic flow on the behavior of the ion current rectification in a conical nanopore connecting two large identical reservoirs is investigated. In particular, the effect of the type of salt is examined by considering LiCl, NaCl, and KCl. We show that neglecting electroosmotic flow is capable of influencing ion current rectification both quantitatively and qualitatively. If electroosmotic flow is neglected, the rectification factor at each level of the applied electric potential bias across the two reservoirs for the case of LiCl (KCl) is always the largest (smallest). However, if electroosmotic flow is taking into account, the relative magnitude of the rectification factors for various salt depends upon the level of the applied electric potential bias. This behavior is consistent with the experimental observation in the literature, and can be explained by the degree of ion deplection/enrichment in a nanopore.

Influence of electroosmotic flow on the ionic current rectification in a pH-regulated, conical nanopore.

The ionic current rectification (ICR) is studied theoretically by considering a pH-regulated, conical nanopore. In particular, the effect of electroosmotic flow (EOF), which was often neglected in previous studies, is investigated by solving a set of coupled Poisson, Nernst-Planck, and Navier-Stokes equations. The behaviors of ICR under various conditions are examined by varying solution pH, bulk ionic concentration, and applied electric potential bias. We show that the EOF effect is significant when the bulk ionic concentration is medium high, the pH is far away from the iso-electric point, and the electric potential bias is high. The percentage deviation in the current rectification ratio arising from neglecting the EOF effect can be on the order of 100%. In addition, the behavior of the current rectification ratio at a high pH taking account of EOF is different both qualitatively and quantitatively from that without taking account of EOF.

Effect of polyethylene glycol on the electrophoretic deposition of hydroxyapatite nanoparticles in isopropanol

Abstract The suspensions of hydroxyapatite (HA) nanoparticles were prepared in isopropanol and polyethylene glycol (PEG) was used as a dispersant. The suspensions were characterized by various tests such as electrical conductivity, zeta potential, Fourier transform infrared spectroscopy (FTIR) and particle size distribution. The results showed that PEG is protonated and then adsorbed on the surface of HA nanoparticles enhancing their stability by an electrosteric stabilization mechanism. Electrophoretic deposition (EPD) was performed at different voltages (60 and 200 V) and times (15, 30, 60, 120, 240 and 360 s). EPD from the suspension with 2 g/L PEG showed the fastest kinetic due to the highest zeta potential (+32.9 mV) of HA nanoparticles in it. The wet density of deposits increased with deposition time and voltage due to the particles rearrangement within it during EPD under the influence of electro-osmotic flow. The SEM images showed that the deposit formed from the suspension with 2 g/L PEG had a finer microstructure with less agglomeration. Optical microscope images showed that PEG acted as an effective binder to prevent from deposit cracking during drying. The coating deposited from the suspension with 2 g/L PEG had the best corrosion resistance in Ringer's solution at 37.5 °C.

Importance of Electroosmotic Flow and Multiple Ionic Species on the Electrophoresis of a Rigid Sphere in a Charge-Regulated Zwitterionic Cylindrical Pore

The influence of electroosmotic flow (EOF) on the electrophoretic behavior of a particle is investigated by considering a rigid sphere in a charge-regulated, zwitterionic cylindrical pore filled with an aqueous solution containing multiple ionic species. This extends conventional analyses to a more general and realistic case. Taking a pore with pK(a) = 7 and pK(b) = 2 (point of zero charge is pH = 2.5) filled with an aqueous NaCl solution as an example, several interesting results are observed. For instance, if pH < 5.5, the particle mobility is influenced mainly by boundary effect, and is influenced by both EOF and boundary effects if pH ≥ 5.5. If pH is sufficiently high, the particle behavior is dominated by EOF, which might alter the direction of electrophoresis. The ratio of (pore radius/particle radius) influences not only the boundary effect, but also the strength of EOF. If the boundary effect is insignificant, the mobility varies roughly linearly with log(bulk salt concentration). These findings are of practical significance to both the interpretation of experimental data and the design of electrophoresis devices.

Microfluidic High-Resolution Free-Flow Isoelectric Focusing

A microfluidic free-flow isoelectric focusing glass chip for separation of proteins is described. Free-flow isoelectric focusing is demonstrated with a set of fluorescent standards covering a wide range of isoelectric points from pH 3 to 10 as well as the protein HSA. With respect to an earlier developed device, an improved microfluidic FFE chip was developed. The improvements included the usage of multiple sheath flows and the introduction of preseparated ampholytes. Preseparated ampholytes are commonly used in large-scale conventional free-flow isoelectric focusing instruments but have not been used in micromachined devices yet. Furthermore, the channel depth was further decreased. These adaptations led to a higher separation resolution and peak capacity, which were not achieved with previously published free-flow isoelectric focusing chips. An almost linear pH gradient ranging from pH 2.5 to 11.5 between 1.2 and 2 mm wide was generated. Seven isoelectric focusing markers were successfully and clearly separated within a residence time of 2.5 s and an electrical field of 20 V mm-1. Experiments with pI markers proved that the device is fully capable of separating analytes with a minimum difference in isoelectric point of Delta(pI) = 0.4. Furthermore, the results indicate that even a better resolution can be achieved. The theoretical minimum difference in isoelectric point is Delta(pI) = 0.23 resulting in a peak capacity of 29 peaks within 1.8 mm. This is an 8-fold increase in peak capacity to previously published results. The focusing of pI markers led to an increase in concentration by factor 20 and higher. Further improvement in terms of resolution seems possible, for which we envisage that the influence of electroosmotic flow has to be further reduced. The performance of the microfluidic free-flow isoelectric focusing device will enable new applications, as this device might be used in clinical analysis where often low sample volumes are available and fast separation times are essential.

Novel elution strategy for monitoring DNA counter-migration in the presence of electroosmotic flow

The migration behavior of native (i.e., unlabelled) DNA in the presence of electroosmotic flow (EOF) was investigated in bare fused-silica capillaries. Employing a novel elution strategy, the influence of EOF on the net mobility of DNA was assessed by collecting the DNA that migrated anodically (i.e., against EOF) and out of the capillary inlet. Various conditions of pH and buffer-zone continuity were employed to characterize this phenomenon. Tris acid (TA, pH 5.14) and Tris base (TB, pH 9.36) were used as buffers in continuous systems, in which the capillary and the inlet reservoir contain the same buffer, and discontinuous systems, in which the capillary contains either TA or TB, and the inlet reservoir contains water. DNA that was ejected into the inlet vial was subsequently analyzed by capillary electrophoresis–laser-induced fluorescence. Both ΦX174/ HaeIII DNA and the β-actin product of single-cell reverse transcriptase-polymerase chain reaction were used as DNA samples in this study. The mechanism of elution was found to depend on bulk flow, in the case of continuous solutions. However, with the discontinuous system, a localized decrease in EOF generated in the capillary tip appeared to impact elution. These findings serve to introduce an alternative approach for characterizing the mobility of highly charged species.