Nok-Kyun Kwo

We consider electroconvective fluid flows initiated by ion concentration polarization (ICP) under pressure-driven shear flow, a scenario often found in many electrochemical devices and systems. Combining scaling analysis, experiment, and numerical modeling, we reveal unique behaviors of ICP under shear flow: a unidirectional vortex structure, its height selection, and vortex advection. Determined by both the external pressure gradient and the electric body force, the dimensionless height of the

We present a novel continuous-flow nanofluidic biomolecule/cell concentrator, utilizing the ion concentration polarization (ICP) phenomenon. The device has one main microchannel which bifurcates into two channels, one for a narrow, concentrated stream and the other for a wider but target-free stream. A nanojunction [cation-selective material (Nafion)] is patterned along the tilted concentrated channel. Application of an electric field generates the ICP zone near the nanojunction so that biomolec

Microfluidic paper-based analytical devices (μPADs) for molecular detection have great potential in the field of point-of-care diagnostics. Currently, a critical problem being faced by μPADs is improving their detection sensitivity. Various preconcentration processes have been developed, but they still have complicated structures and fabrication processes to integrate into μPADs. To address this issue, we have developed a novel paper-based preconcentrator utilizing ion concentration polarization

Chloride ion, the majority salt in nature, is ∼52% faster than sodium ion (DNa+ = 1.33, DCl- = 2.03[10(-9)m(2)s(-1)]). Yet, current electrochemical desalination technologies (e.g. electrodialysis) rely on bipolar ion conduction, removing one pair of the cation and the anion simultaneously. Here, we demonstrate that novel ion concentration polarization desalination can enhance salt removal under a given current by implementing unipolar ion conduction: conducting only cations (or anions) with the

We present a novel paper-based flow fractionation system for preconcentration and field-flow separation. In this passive fluidic device, a straight channel is divided into multiple daughter channels, each of which is connected with an expanded region. The hydrodynamic resistance of the straight channel is predominant compared with those of expanded regions, so we can create steady flows through the straight and daughter channels. While the expanded regions absorb a great amount of water via capi

Sheltering of a perturbed vortical layer by a shear flow is a common method to control turbulence and transport in plasma physics. Despite the desire to exploit this phenomenon in wider engineering applications, shear sheltering has rarely been observed in general non-ionized fluids. In this study, we visualize this shear sheltering in a generic neutral-fluid situation in electromembrane desalination: electroconvection (EC) under the Hagen–Poiseuille flow initiated by ion concentration polarizat

The ion concentration polarization (ICP) phenomenon at micronanofluidic interfaces has been extensively utilized to preconcentrate low-abundance biological samples. Although preconcentration by ICP is robust, its multiphysics phenomenon does not permit a clear prediction of the preconcentration conditions and sites. Here, we present a new method for spatiotemporally defining preconcentration, which can generate target-condensed plugs in a very specific region (<100 μm) regardless of the operatin

Efficient pathogen enrichment and nucleic acid isolation are critical for accurate and sensitive diagnosis of infectious diseases, especially those with low pathogen levels. Our study introduces a biporous silica nanofilms-embedded sample preparation chip for pathogen and nucleic acid enrichment/isolation. This chip features unique biporous nanostructures comprising large and small pore layers. Computational simulations confirm that these nanostructures enhance the surface area and promote the f

Sensory neurons generate spike patterns upon receiving external stimuli and encode key information to the spike patterns, enabling energy-efficient external information processing. Herein, we report an epifluidic electronic patch with spiking sweat clearance using a sensor containing a vertical sweat-collecting channel for event-driven, energy-efficient, long-term wireless monitoring of epidermal perspiration dynamics. Our sweat sensor contains nanomesh electrodes on its inner wall of the channe

Bridging the gap: Vacuum-assisted capillary force lithography (CFL) allows the fabrication of monolithic, suspended bridge structures (see picture) by exploiting partial curing kinetics and vacuum-assisted hydraulic filling. A small portion of the base microstructure (<4 µm) is molded to create a bridge structure by simply applying a nanoscale mold with the impression of channels, meshes, or circles.