ORCID Profile
0000-0002-5451-4301
Current Organisation
University of Tokyo
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Publisher: Elsevier BV
Date: 03-2023
Publisher: Elsevier BV
Date: 03-2021
Publisher: American Chemical Society (ACS)
Date: 05-09-2022
Publisher: American Chemical Society (ACS)
Date: 09-09-2016
DOI: 10.1021/ACS.ANALCHEM.6B02513
Abstract: The control of biomolecule translocation through nanopores is important in nanopore protein detection. Improvement in current nanopore molecule control is desired to enhance capture rates, extend translocation times, and ensure the effective detection of various proteins in the same solutions. We present a method that simultaneously resolves these issues through the use of a gate-modulated conical nanopore coupled with solutions of varying salt concentration. Simulation results show that the presence of an induced reverse electroosmotic flow (IREOF) results in inlet flows from the two ends of the nanopore centerline entering into the nanopore in opposite directions, which simultaneously elevates the capture rate and immobilizes the protein in the nanopore, thus enabling steady current blockage measurements for a range of proteins. In addition, it is shown that proteins with different size/charge ratios can be trapped by a gate modulation intensified flow field at a similar location in the nanopore in the same solution conditions.
Publisher: American Chemical Society (ACS)
Date: 29-12-2020
Publisher: Wiley
Date: 12-09-2021
Abstract: 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.
Publisher: American Chemical Society (ACS)
Date: 15-09-2010
DOI: 10.1021/LA102631Q
Abstract: The diffusiophoresis of a soft spherical particle normal to two parallel disks subject to an applied ionic concentration gradient is modeled theoretically. The soft particle, which comprises a rigid core and a porous membrane layer, is capable of simulating a wide class of particles such as biocolloids and particles covered by an artificial membrane layer a rigid particle can also be recovered as the limiting case where the membrane layer is infinitely thin. The problem considered simulates, for ex le, the chemotaxis of cells or microorganisms. We show that the presence of the membrane layer is capable of yielding complicated diffusiophoretic behavior when the sign of the charge carried by that layer is different from that on the surface of the rigid core of the particle. Both the sign and the magnitude of the diffusiophoretic velocity of a particle can be adjusted through varying the friction coefficient of its membrane layer. These results are of practical significance, for ex le, in the case where diffusiophoresis is adopted as a separation operation or as a tool to carry and/or control the rate of drug release.
Publisher: American Physical Society (APS)
Date: 15-11-2022
Publisher: American Chemical Society (ACS)
Date: 09-07-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3TA03018K
Abstract: Understanding the relationship between the geometry of metal-organic frameworks (MOFs) and the CO 2 enthalpy of adsorption is of utmost importance to control CO 2 adsorption/desorption in MOFs and the associated heat...
Publisher: Elsevier BV
Date: 05-2019
Publisher: American Chemical Society (ACS)
Date: 13-09-2017
Publisher: Wiley
Date: 22-01-2021
Publisher: Elsevier BV
Date: 2018
Publisher: American Chemical Society (ACS)
Date: 25-07-2019
DOI: 10.1021/ACS.LANGMUIR.9B01261
Abstract: The effect of pore length on the water filling and emptying rates was studied using mesoporous silica (MPS) with same pore diameter but different pore lengths. The pore diameter of the synthesized MPS was ∼8 nm, whereas the average pore lengths were 460, 1,770, and 4000 nm. The gravimetric method was employed to record the time course of the adsorbed mass of water in MPS at 298 K and 1 atm. In both the filling and emptying processes, the relaxation curves (time course of adsorbed mass of water per unit mass of s le) were not significantly related to the pore length. This independence of the initial adsorption and desorption rates on the pore length suggests that the surface of the MPS aggregates is the bottleneck in the overall adsorption and desorption processes and that the initial mass flux in each nanopore is inversely proportional to the pore length. Furthermore, because the relaxation times to reach the equilibrium state were independent of the pore length, the mass flux of water uptake, release, and transport probably increase with an increase in the pore length during the entire adsorption and desorption processes. A transport model to describe these phenomena was proposed.
Publisher: American Chemical Society (ACS)
Date: 18-12-2019
Abstract: A thermodynamic stability analysis of microbubbles in an enclosed volume of a volatile liquid-noncondensable gas solution was performed. The stability conditions for the formation of the bubbles and the relationship between the equilibrium bubble radius and the equilibrium bubble number were investigated. The calculation results show that even if the saturation vapor pressure of a volatile liquid is higher than the pressure of the liquid phase, stable noncondensable gas bubbles appear in a closed system. Under such a condition, if the initial pressure of the noncondensable gas, which is proportional to the total number of moles of a noncondensable gas in the system, increases, stable bubbles appear at a lower temperature. At a fixed parameter of h
Publisher: American Chemical Society (ACS)
Date: 14-08-2014
DOI: 10.1021/AC501875U
Abstract: Isoelectric focusing of proteins in a silica nanofluidic channel filled with citric acid and disodium phosphate buffers is investigated via numerical simulation. Ions in the channel migrate in response to (i) the electric field acting on their charge and (ii) the bulk electroosmotic flow (which is directed toward the cathode). Proteins are focused near the low pH (anode) end when the electromigration effect is more significant and closer to the high pH (cathode) end when the electroosmotic effect dominates. We simulate the focusing behavior of Dylight labeled streptavidin (Dyl-Strep) proteins in the channel, using a relationship between the protein's charge and pH measured in a previous experiment. Protein focusing results compare well to previous experimental measurements. The effect of some key parameters, such as applied voltage, isoelectric point (pI), bulk pH, and bulk conductivity, on the protein trapping behavior in a nanofluidic channel is examined.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4LC00504J
Abstract: Concentration gradient focusing and separation in a silica nanofluidic channel with a non-uniform electroosmotic flow.
Publisher: Elsevier BV
Date: 02-2010
DOI: 10.1016/J.JCIS.2009.10.043
Abstract: The diffusiophoresis of a charged spherical particle along the axis of an uncharged cylindrical pore filled with an electrolyte solution is analyzed theoretically. The influence of chemiphoresis, which includes two types of double-layer polarization, and that of electrophoresis arising from the difference in the diffusivities of the ionic species on the diffusiophoretic behavior of the particle are discussed. We have underlined the important difference between two cases: the first is a possibility for a particle to migrate to the low concentration side at low surface potentials ( approximately 25mV) along the axis of a cylindrical pore, while the second is that this migration occurs at high surface potentials ( approximately 150mV) in the case of a sphere in a spherical cavity.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9TA12065C
Abstract: The guest-induced structural changes in LMOF-201 were demonstrated by using reactive force field combined with Grand Canonical Monte Carlo and molecular dynamics simulations.
Publisher: Elsevier BV
Date: 2018
Publisher: American Chemical Society (ACS)
Date: 03-12-2018
Publisher: American Chemical Society (ACS)
Date: 22-11-2021
Publisher: American Chemical Society (ACS)
Date: 29-04-2014
DOI: 10.1021/LA500206B
Abstract: Previous work has demonstrated the simultaneous concentration and separation of proteins via a stable ion concentration gradient established within a nanochannel (Inglis Angew. Chem., Int. Ed. 2001, 50, 7546-7550). To gain a better understanding of how this novel technique works, we here examine experimentally and numerically how the underlying electric potential controlled ion concentration gradients can be formed and controlled. Four nanochannel geometries are considered. Measured fluorescence profiles, a direct indicator of ion concentrations within the Tris-fluorescein buffer solution, closely match depth-averaged fluorescence profiles calculated from the simulations. The simulations include multiple reacting species within the fluid bulk and surface wall charge regulation whereby the deprotonation of silica-bound silanol groups is governed by the local pH. The three-dimensional system is simulated in two dimensions by averaging the governing equations across the (varying) nanochannel width, allowing accurate numerical results to be generated for the computationally challenging high aspect ratio nanochannel geometries. An electrokinetic circuit analysis is incorporated to directly relate the potential drop across the (simulated) nanochannel to that applied across the experimental chip device (which includes serially connected microchannels). The merit of the thick double layer, potential-controlled concentration gradient as a particle focusing and separation tool is discussed, linking this work to the previously presented protein trapping experiments. We explain why stable traps are formed when the flow is in the opposite direction to the concentration gradient, allowing particle separation near the low concentration end of the nanochannel. We predict that tapered, rather than straight nanochannels are better at separating particles of different electrophoretic mobilities.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8NR02016G
Abstract: The difference in adsorption and desorption characteristics depending on the hydrophilicity arrangements within a nanopore.
Publisher: American Chemical Society (ACS)
Date: 02-06-2010
DOI: 10.1021/JP1039157
Abstract: The influences of a boundary and the shape of a particle on its diffusiophoretic behavior are examined by considering the diffusiophoresis of a charged ellipsoid along the axis of an uncharged cylindrical pore filled with electrolyte solutions. The diffusiophoretic mobility of the particle under various conditions is evaluated through varying the particle aspect ratio, the size of the particle, the thickness of the double layer, the diffusivities of co-ions and counterions, and the level of the surface potential. Because the double-layer polarization, the electrophoresis effect, the boundary effect, and the electrical interaction between the particle and the co-ions outside the double layer all play a role, the diffusiophoretic behavior of the particle is complicated. For a fixed particle volume, the relative magnitude of the diffusiophoretic mobilities of particles of various shapes depends highly on the degree of the boundary effect. It is possible for a particle to migrate toward the low-concentration side, regardless of the level of the surface potential, which is not observed in the case of a sphere in a planar slit or in a spherical cavity.
Publisher: Elsevier BV
Date: 03-2022
Publisher: American Chemical Society (ACS)
Date: 09-02-2010
DOI: 10.1021/JP907696T
Abstract: The diffusiophoresis of a charge-regulated spherical particle normal to two parallel disks as a response to an applied uniform electrolyte concentration gradient is modeled theoretically. The fixed charge on the particle surface comes from the dissociation/association reactions of the functional groups, yielding a charge-regulated surface, which simulates biological cells. Numerical simulations are conducted to examine the behavior of a particle under various conditions: the parameters considered in the simulation include the thickness of the double layer, the charged conditions on the particle surface, the relative size of the particle, and the particle-disk distance. Because the diffusiophoretic mobility of a particle can be dominated by chemiphoresis, electrophoresis, or osmotic flow, the diffusiophoretic behavior of the particle is complicated. For instance, the diffusiophoretic mobility may have two local maximums and a local minimum as the thickness of the double layer varies. This behavior is of practical significance if diffusiophoresis is adopted as a separation operation or as a tool to characterize the surface properties of a particle.
Publisher: Elsevier BV
Date: 08-2016
DOI: 10.1016/J.CIS.2016.05.001
Abstract: The manipulation of biomolecules, fluid and ionic current in a new breed of integrated nanofluidic devices requires a quantitative understanding of electrokinetics at the silica/water interface. The conventional capacitor-based electrokinetic Electric Double Layer (EDL) models for this interface have some known shortcomings, as evidenced by a lack of consistency within the literature for the (i) equilibrium constants of surface silanol groups, (ii) Stern layer capacitance, (iii) zeta (ζ) potential measured by various electrokinetic methods, and (iv) surface conductivity. In this study, we consider how the experimentally observable viscoelectric effect - that is, the increase of the local viscosity due to the polarisation of polar solvents - affects electrokinetcs at the silica/water interface. Specifically we consider how a model that considers viscoelectric effects (the VE model) performs against two conventional electrokinetic models, namely the Gouy-Chapman (GC) and Basic Stern capacitance (BS) models, in predicting four fundamental electrokinetic phenomena: electrophoresis, electroosmosis, streaming current and streaming potential. It is found that at moderate to high salt concentrations (>5×10(-3)M) predictions from the VE model are in quantitative agreement with experimental electrokinetic measurements when the sole additional adjustable parameter, the viscoelectric coefficient, is set equal to a value given by a previous independent measurement. In contrast neither the GS nor BS models is able to reproduce all experimental data over the same concentration range using a single, robust set of parameters. Significantly, we also show that the streaming current and potential in the moderate to high surface charge range are insensitive to surface charge behaviour (including capacitances) when viscoelectric effects are considered, in difference to models that do not consider these effects. This strongly questions the validity of using pressure based electrokinetic experiments to measure surface charge characteristics within this experimentally relevant high pH and moderate to high salt concentration range. At low salt concentrations (<5×10(-3)M) we find that there is a lack of consistency in previously measured channel conductivities conducted under similar solution conditions (pH, salt concentration), preventing a conclusive assessment of any model suitability in this regime.
Publisher: Elsevier BV
Date: 05-2011
Publisher: Wiley
Date: 03-2012
Abstract: The diffusiophoresis of a polyelectrolyte subject to an applied salt concentration gradient is modeled theoretically. The entirely porous type of particle is capable of simulating entities such as DNA, protein, and synthetic polymeric particles. The dependence of the diffusiophoretic behavior of the polyelectrolyte on its physical properties, and the types of ionic species and their bulk concentrations are discussed in detail. We show that in addition to the effects coming from the polarization of double layer and the difference in the ionic diffusivities, the polarization of the condensed counterions inside the polyelectrolyte might also be significant. The last effect, which has not been reported previously, reduces both the electric force and the hydrodynamic force acting on the polyelectrolyte. Both the direction and the magnitude of the diffusiophoretic velocity of the polyelectrolyte are found to highly depend upon its physical properties. These results provide valuable references for applications such as DNA sequencing and catalytic nano- or micromotors.
Publisher: AIP Publishing
Date: 12-04-2021
DOI: 10.1063/5.0040909
Abstract: Molecular dynamics simulations of water adsorbed in Material Institute Lavoisier MIL-101(Cr) metal–organic frameworks are performed to analyze the kinetic properties of water molecules confined in the framework at 298.15 K and under different vapor pressures and clarify the water adsorption mechanism in MIL-101(Cr). The terahertz frequency-domain spectra (THz-FDS) of water are calculated by applying fast Fourier transform to the configurational data of water molecules. According to the characteristic frequencies in the THz-FDS, the dominant motions of water molecules in MIL-101(Cr) can be categorized into three types: (1) low-frequency translational motion (0–0.5 THz), (2) medium-frequency vibrational motion (2–2.5 THz), and (3) high-frequency vibrational motion (& THz). Each type of water motion is confirmed by visualizing the water configuration in MIL-101(Cr). The ratio of the number of water molecules with low-frequency translational motion to the total number of water molecules increases with the increase in vapor pressure. In contrast, that with medium-frequency vibrational motion is found to decrease with vapor pressure, exhibiting a pronounced decrease after water condensation has started in the cavities. That with the high-frequency vibrational motion is almost independent of the vapor pressure. The interactions between different types of water molecules affect the THz-FDS. Furthermore, the self-diffusion coefficient and the velocity auto-correlation function are calculated to clarify the adsorption state of the water confined in MIL-101(Cr). To confirm that the general trend of the THz-FDS does not depend on the water model, the simulations are performed using three water models, namely, rigid SPC/E, flexible SPC/E, and rigid TIP5PEw.
Publisher: American Physical Society (APS)
Date: 18-10-2021
Publisher: American Chemical Society (ACS)
Date: 25-02-2010
DOI: 10.1021/LA904726K
Abstract: The diffusiophoresis of a charge-regulated spherical particle along the axis of a cylindrical pore is modeled. The problem considered allows us to examine simultaneously the effects of the presence of a boundary, the charge conditions on the particle surface, the thickness of the double layer, and the nature of a dispersion medium including its pH value and the diffusivities of the ionic species with respect to the diffusiophoretic behavior of a particle. We show that, in addition to the factors of double-layer polarization, electrophoresis, and the osmotic flow of solvent, the diffusiophoretic behavior of the particle can also be affected significantly by the electrical repulsive interaction between the particle and the co-ions immediately outside the double layer as they diffuse through the gap between the double layer and the pore. The last effect, which can influence the diffusiophoretic behavior of a particle both quantitatively and qualitatively, is absent in the diffusiophresis of a sphere in a spherical cavity. The competition of those effects yields many interesting results that are of practical significance in the design of a diffusiophoretic apparatus and/or the interpretation of experimental data.
Publisher: American Chemical Society (ACS)
Date: 06-2009
DOI: 10.1021/JP9014417
Abstract: The boundary effect on the diffusiophoresis of a colloidal particle is investigated theoretically by considering a soft spherical particle at an arbitrary position in a spherical cavity. The particle, which comprises a rigid core and an ion-penetrable layer, simulates biocolloids and particles covered by an artificial membrane layer. The diffusiophoretic behavior of the particle is governed by two types of DLP, the electrophoresis arising from the difference in the diffusivities of ionic species and diffusioosmotic flow. The influences of the thickness of the double layer, the size of the cavity, and the nature and the position of the particle on its diffusiophoretic behavior are discussed. We show that the presence of a boundary can have a profound influence on the behavior of a particle. The effect of electrophoresis can also lead to interesting diffusiophoretic behavior.
Publisher: American Chemical Society (ACS)
Date: 23-10-2018
DOI: 10.1021/ACSSENSORS.8B00635
Abstract: 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.
Publisher: Elsevier BV
Date: 2019
Publisher: American Chemical Society (ACS)
Date: 05-01-2009
DOI: 10.1021/LA803334A
Abstract: The boundary effect on the diffusiophoretic behavior of a particle is analyzed theoretically by considering the diffusiophoresis of a charged sphere under arbitrary surface potential and double-layer thickness at an arbitrary position in an uncharged spherical cavity. We show that the phenomenon under consideration is governed by double-layer relaxation, chemiosmotic/diffusioosmotic flow, and two types of competing double-layer polarization. The presence of the cavity has a profound influence on the diffusiophoretic behavior of the particle, especially when the surface potential is high. For instance, the scaled diffusiophoretic velocity of the particle has a local maximum as the position of the particle varies it may have a local maximum and local minimum as the thickness of the double-layer varies. The significance of the effect of double-layer relaxation depends upon the level of surface potential and magnitude of the electric Peclet number.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7NR04387B
Abstract: When the temperature and ion concentration are very high, hydrophobic patches grow owing to extraction of gases from the solution.
No related grants have been discovered for Wei-Lun Hsu.