The electric field strength in orifice-like nanopores of ultrathin membranes

Advancement of electroosmotic pump in microflow analysis: A review

This review (with 152 references) covers the progress made in the development and application of electroosmotic pumps in a period from 2009 through 2018 in microflow analysis. Following a short introduction, the review first categorizes various electroosmotic pumps into five subclasses based on the materials used for pumping: i) open channel EOP, 2) packed-column EOP, iii) porous monolith EOP, iv) porous membrane EOP, and v) other types of EOP. Pumps in each subclass are discussed. A next section covers EOP applications, primarily the applications of EOPs in micro flow analysis and micro/nano liquid chromatography. Other scattered applications are also examined. Perspectives, trends and challenges are discussed in the final section.

Brownian dynamics simulations of the ionic current traces for a neutral nanoparticle translocating through a nanopore

In this work, the ionic current blockades due to the translocation of a neutral spherical nanoparticle through a nanopore in a solid state membrane are computed. We use a Brownian dynamics approach, in conjunction with a full three-dimensional self-consistent solution of the Poisson-Nernst-Planck and Navier-Stockes system of equations to describe realistic ionic current response arising due to the random motion of a nanoparticle through a nanopore. We find that in addition to the usual geometric blockade, the variations of the current along the axis of the pore are largely caused by a concentration polarization induced by the presence of the translocating nanoparticle in the nanopore while the current changes in the radial (perpendicular to the axis) direction occur because of the local build up of the ionic charge between the particle and the nanopore surface. By performing statistical analysis of the current traces, we also observe that, in general, smaller current blockade values correspond to faster translocation times, while increased dwell times result in a larger current decrease.

Electro-osmotic flow through nanopores in thin and ultrathin membranes

We theoretically study how the electro-osmotic fluid velocity in a charged cylindrical nanopore in a thin solid state membrane depends on the pore's geometry, membrane charge, and electrolyte concentration. We find that when the pore's length is comparable to its diameter, the velocity profile develops a concave shape with a minimum along the pore axis unlike the situation in very long nanopores with a maximum velocity along the central pore axis. This effect is attributed to the induced pressure along the nanopore axis due to the fluid flow expansion and contraction near the exit or entrance to the pore and to the reduction of electric field inside the nanopore. The induced pressure is maximal when the pore's length is about equal to its diameter while decreasing for both longer and shorter nanopores. A model for the fluid velocity incorporating these effects is developed and shown to be in a good agreement with numerically computed results.

Modification of Nanoporous Silicon Nitride with Stable and Functional Organic Monolayers

This study describes the formation of functional organic monolayers on thin, nanoporous silicon nitride membranes. We demonstrate that the vapor-phase carbene insertion into the surface C-H bonds can be used to form sub-5 nm molecular coatings on nanoporous materials, which can be further modified with monolayers of polyethylene glycol (PEG) molecules. We investigate composition, thickness, and stability of the functionalized monolayers and the changes in the membrane permeability and pore size distribution. We show that, due to the low coating thickness (~7 nm), the functionalized membrane retains 80% of the original gas permeance and 40% of the original hydraulic permeability. We also show that the carbene/PEG functionalization is hydrolytically stable for up to 48 h of exposure to water and that it can suppress nonspecific adsorption of the proteins BSA and IgG. Our results suggest that the vapor-phase carbenylation can be used as a complementary technology to the traditional self-assembly and polymer brush chemistries in chemical functionalization of nanoporous materials, which are limited in their ability to serve as stable coatings that do not occlude nanomembrane pores.

Quantitative estimation of electro-osmosis force on charged particles inside a borosilicate resistive-pulse sensor

Nano and micron-scale pore sensors have been widely used for biomolecular sensing application due to its sensitive, label-free and potentially cost-effective criteria. Electrophoretic and electroosmosis are major forces which play significant roles on the sensor's performance. In this work, we have developed a mathematical model based on experimental and simulation results of negatively charged particles passing through a 2μm diameter solid-state borosilicate pore under a constant applied electric field. The mathematical model has estimated the ratio of electroosmosis force to electrophoretic force on particles to be 77.5%.

Nanoporous membrane robustness / stability in small form factor microfluidic filtration system

The development of wearable hemodialysis (HD) devices that replace center-based HD holds the promise to improve both outcomes and quality-of-life for patients with end-stage-renal disease (ERD). A prerequisite for these devices is the development of highly efficient membranes that can achieve high toxin clearance in small footprints. The ultrathin nanoporous membrane material developed by our group is orders of magnitude more permeable than conventional HD membranes. We report on our progress making a prototype wearable dialysis unit. First, we present data from benchtop studies confirming that clinical levels of urea clearance can be obtained in a small animal model with low blood flow rates. Second, we report on efforts to improve the mechanical robustness of high membrane area dialysis devices.