Jonathan Posner

• Professor (Associate) at University of Washington

Background Tenofovir diphosphate concentration in red blood cells is an objective measure of long-term oral pre-exposure prophylaxis (PrEP) or antiretroviral therapy (ART) adherence. However, current methods for measuring tenofovir diphosphate are equipment and capital intensive, limiting widespread adoption. Objectives Low cost, rapid diagnostics...

Isothermal nucleic acid amplification tests are a vital tool for point-of-care diagnostics. In this work, we significantly improve paper-based recombinase polymerase amplification of HIV-1 DNA and RNA by employing a vibration-based mixing platform.

OBJECTIVES/GOALS: Current COVID-19 rapid molecular tests require cartridge-reader detection, expensive circuitry, and complex microfluidics making the most accurate tests unavailable to the masses. Here we present a rapid molecular diagnostic leveraging isothermal amplification and paper-based microfluidics for a low-cost ultra-sensitive COVID-19 a...

Over 71 million people are infected with hepatitis C virus (HCV) worldwide, and approximately 400,000 global deaths result from complications of untreated chronic HCV. Pan-genomic direct-acting antivirals (DAAs) have recently become widely available and feature high cure rates in less than 12 weeks of treatment. The rollout of DAAs is reliant on di...

Sufficient drug concentrations are required for efficacy of antiretroviral drugs used in HIV care and prevention. Measurement of nucleotide analogs, included in most HIV medication regimens, enables monitoring of short‐ and long‐term adherence and the risk of treatment failure. The REverSe TRanscrIptase Chain Termination (RESTRICT) assay rapidly in...

Quantitative nucleic acid amplification tests (qNAATs) are critical in treating infectious diseases, such as in HIV viral load monitoring or SARS-CoV-2 testing, in which viral load indicates viral suppression or infectivity. Quantitative PCR is the gold standard tool for qNAATs; however, there is a need to develop point-of-care (POC) qNAATs to mana...

Current HIV antiretroviral therapy (ART) or pre-exposure prophylaxis (PrEP) therapy adherence monitoring relies on either patient self-reported adherence or monitored drug dispensing, which are not reliable. We report a proof-of-concept adherence monitoring assay which directly measures nucleotide reverse transcriptase inhibitor (NRTI) concentratio...

Quantitative nucleic acid amplification tests (qNAATs) are critical in treating infectious diseases, such as in HIV viral load monitoring or SARS-CoV-2 testing, in which viral load indicates viral suppression or infectivity. Quantitative PCR is the gold standard tool for qNAATs; however, there is a need to develop point-of-care (POC) qNAATs to mana...

Sufficient drug concentrations are required for efficacy of antiretroviral drugs used in human immunodeficiency virus (HIV) care and prevention. Measurement of nucleotide analogs, included in most HIV medication regimens, enables monitoring of short- and long-term adherence and the risk of treatment failure. The REverSe TRanscrIptase Chain Terminat...

The number of people living with HIV continues to increase with the current total near 38 million, of which about 26 million are receiving antiretroviral therapy (ART). These treatment regimens are highly effective when properly managed, requiring routine viral load monitoring to assess successful viral suppression. Efforts to expand access by dece...

The COVID-19 pandemic has put the spotlight on the urgent need for integrated nucleic acid tests (NATs) for infectious diseases, especially those that can be used near patient ("point-of-care", POC), with rapid results and low cost, but without sacrificing sensitivity or specificity of gold standard PCR tests. In the US, the Clinical Laboratory Imp...

Objective Maintaining adequate drug adherence is crucial to ensure the HIV prevention benefits of pre-exposure prophylaxis (PrEP). We developed an enzymatic assay for rapidly measuring tenofovir-diphosphate (TFV-DP) concentrations—a metabolite that indicates long-term PrEP adherence. Setting The study was conducted at the Madison HIV Clinic at Har...

Many motile cells exhibit migratory behaviors, such as chemotaxis (motion up or down a chemical gradient) or chemokinesis (dependence of speed on chemical concentration), which enable them to carry out vital functions including immune response, egg fertilization, and predator evasion. These have inspired researchers to develop self-propelled colloi...

p>The number of people living with HIV continues to increase with the current total near 38 million, of which about 26 million are receiving antiretroviral therapy. These treatment regimens are highly effective when properly managed, requiring routine viral load monitoring to assess successful viral suppression. Efforts to expand access by decentra...

Nucleic acid amplification tests (NAATs) are a crucial diagnostic and monitoring tool for infectious diseases. A key procedural step for NAATs is sample preparation: separating and purifying target nucleic acids from crude biological samples prior to nucleic acid amplification and detection. Traditionally, sample preparation has been performed with...

Current HIV antiretroviral (ART) or pre-exposure prophylaxis (PrEP) therapy adherence monitoring relies on either patient self-reported adherence or monitoring drug dispensing, which are not reliable. We propose an objective adherence monitoring assay which directly measures nucleotide reverse transcriptase inhibitor (NRTI) concentration using a re...

Objective: Maintaining adequate drug adherence is crucial to ensure the HIV prevention benefits of pre-exposure prophylaxis (PrEP). We developed an enzymatic assay for rapidly measuring tenofovir-diphosphate (TFV-DP) concentrations – a metabolite that indicates long-term PrEP adherence. Setting: The study was conducted at the Madison HIV Clinic at...

Objective: Maintaining adequate drug adherence is crucial to ensure the HIV prevention benefits of pre-exposure prophylaxis (PrEP). We developed an enzymatic assay for rapidly measuring tenofovir-diphosphate (TFV-DP) concentrations – a metabolite that indicates long-term PrEP adherence. Setting: The study was conducted at the Madison HIV Clinic at...

Many motile cells exhibit migratory behaviors, such as chemotaxis (motion up or down a chemical gradient) or chemokinesis (when speed depends on concentration), which enable them to carry out vital functions including immune response, egg fertilization, and predator evasion. These have inspired researchers to develop self-propelled colloidal analog...

There are ongoing research efforts into simple and low-cost point-of-care (POC) nucleic acid amplification tests (NATs) addressing widespread diagnostic needs in resource-limited clinical settings. Nucleic acid testing for RNA targets in blood specimens typically requires sample preparation that inactivates robust blood ribonucleases (RNases) that...

Poor adherence to pre-exposure prophylaxis (PrEP) and antiretroviral therapy (ART) can lead to human immunodeficiency virus (HIV) acquisition and emergence of drug resistant infections, respectively. Measurement of antiviral drug levels provides objective adherence information that may help prevent adverse health outcomes. Gold standard drug-level...

Poor adherence to pre-exposure prophylaxis (PrEP) and antiretroviral therapy (ART) can lead to human immunodeficiency virus (HIV) acquisition and emergence of drug resistant infections, respectively. Measurement of antiviral drug levels provides objective adherence information that may help prevent adverse health outcomes. Gold standard drug-level...

The global public health community has set ambitious treatment targets to end the HIV/AIDS pandemic. With the notable absence of a cure, the goal of HIV treatment is to achieve sustained suppression of an HIV viral load, which allows for immunological recovery and reduces the risk of onward HIV transmission. Monitoring HIV viral load in people livi...

Nucleic acid amplification tests (NAATs) provide high diagnostic accuracy for infectious diseases and quantitative results for monitoring viral infections. The majority of NAATs require complex equipment, cold chain dependent reagents, and skilled technicians to perform tests. This largely confines NAATs to centralized laboratories and can signific...

There is a need to measure dynamic tactile information to enhance robotic hand performance during haptic exploration and object manipulation. Here, we report on the dynamic characterization of a flexible, bioinspired, resistive microfluidic shear force sensor skin. When the skin is subjected to shear force, one side of the skin experiences tension...

There is a need to gather rich, real-time tactile information to enhance robotic hand performance during haptic exploration and object manipulation. Measuring shear forces is useful for grasping and manipulating objects; however, there are limited effective shear sensing strategies that are compatible with existing end effectors. Here, we report a...

It is well-known that micro- and nanoparticles can move by phoretic effects in response to externally imposed gradients of scalar quantities such as chemical concentration or electric potential. A class of active colloids can propel themselves through aqueous media by generating local gradients of concentration and electrical potential via surface...

As lab-on-a-chip health diagnostic technologies mature, there is a push to translate them from the laboratory to the clinic. For these diagnostics to achieve maximum impact on patient care, scientists and engineers developing the tests should understand the analytical and clinical statistical metrics that determine the efficacy of the test. Appreci...

Shape of engineered nanomaterials (ENMs) can be used as a design handle to achieve controlled manipulation of physicochemical properties. This tailored material property approach necessitates the establishment of relationships between specific ENM properties that result from such manipulations (e.g., surface area, reactivity, or charge) and the obs...

This tutorial review focuses on aqueous slurries of dispersed engineered nanoparticles (ENPs) used in chemical mechanical planarization (CMP) for polishing wafers during manufacturing of semiconductors. A research consortium was assembled to procure and conduct physical, chemical, and in vitro toxicity characterization of four ENPs used in CMP. Bas...

Nucleic acid amplification tests are the gold standard for many infectious disease diagnoses due to high sensitivity and specificity, rapid operation, and low limits of detection. Despite the advantages of nucleic acid amplification tests, they currently offer limited point-of-care (POC) utility due to the need for complex instruments and laborious...

Lateral flow (LF) immunoassays are one of the most prevalent point-of-care (POC) diagnostics due to their simplicity, low cost, and robust operation. A common criticism of LF tests is that they have poor detection limits compared to analytical techniques, like ELISA, which confines their application as a diagnostic tool. The low detection limit of...

An electroosmotic (EO) pump is provided that includes a housing having a pump cavity, a porous core medium and electrodes. The porous core medium is positioned within the pump cavity to form an exterior reservoir that extends at least partially about an exterior surface of the porous core medium. The porous core medium has an open inner chamber pro...

Paper substrates have been widely used to construct point-of-care lateral flow immunoassays (LFIA) diagnostic devices. Paper based microfluidic devices are robust and relatively simple to operate, compared to channel microfluidic devices, which is perhaps their greatest advantage and the reason they have reached a high level of commercial success....

Styrene-ethylene/butylene-styrene (SEBS) copolymers combine thermoplastic and elastomeric properties to provide microdevices with the advantageous properties of hard thermoplastics and ease of fabrication similar to PDMS. This work describes the electrical surface properties of SEBS block copolymers using current monitoring experiments to determine...

Catalytic bimetallic Janus particles swim by a bipolar electrochemical propulsion mechanism that results from electroosmotic fluid slip around the particle surface. The flow is driven by electrical body forces which are generated from a coupling of a reaction-induced electric field and net charge in the diffuse layer surrounding the particle. This...

Engineered nanomaterials (ENMs) have attractive functional properties and are increasingly being used in commercial products. However, ENMs present health risks that are poorly understood and difficult to assess. Because ENMs must interface with cell membranes to cause biological effects, improved methods are needed to measure ENM-biomembrane inter...

In this work, we introduce a simple solvent-assisted micromolding technique for the fabrication of high-fidelity styrene-ethylene/butylene-styrene (SEBS) microfluidic devices with high polystyrene (PS) content (42 wt% PS, SEBS42). SEBS triblock copolymers are styrenic thermoplastic elastomers that exhibit both glassy thermoplastic and elastomeric p...

Spherical catalytic micromotors fabricated as described in Wheat et al. [Langmuir 26, 13052 (2010)] show fuel concentration dependent translational and rotational velocity. The motors possess short-time and long-time diffusivities that scale with the translational and rotational velocity with respect to fuel concentration. The short-time diffusivit...

Due to the widespread use of engineered nanomaterials (ENMs) in consumer and industrial products, concerns have been raised over their impacts once released into the ecosystems. While there has been a wealth of studies on the short-term acute toxic effects of ENMs over the past decade, work on the chronic endpoints, such as biological accumulation,...

In this work, we investigated multiple vortical flows inside the ion concentration polarization (ICP) layer that forms due to a coupling of applied electric fields and the semipermeable nanoporous junction between microchannels. While only a primary vortex near perm-selective membrane is traditionally known to lead to electrokinetic instability, mu...

Lipid bilayers are biomembranes common to cellular life and constitute a continuous barrier between cells and their environment. Understanding the interaction of engineered nanomaterials (ENMs) with lipid bilayers is an important step toward predicting subsequent biological effects. In this study, we assess the effect of varying the surface functio...

We present an investigation of chaotic dynamics of a low Reynolds number electrokinetic flow. Electrokinetic flows arise due to couplings of electric fields and electric double layers. In these flows, applied (steady) electric fields can couple with ionic conductivity gradients outside electric double layers to produce flow instabilities. The thres...

We present a diagnostic platform for measuring three-dimensional three-component (3D3C) velocity fields in microscopic volumes. The imaging system uses high-speed Nipkow spinning disk confocal microscopy. Confocal microscopy provides optical sectioning using pinhole spatial filtering which rejects light originating from out-of-focus objects. The sy...

Robotic applications often require robust tactile sensing capabilities on curved surfaces, such as artificial fingertips. Flexible tactile sensors could be conformally wrapped around curved digits and could enhance grip by cushioning impacts and increasing the effective contact area during grasp. Flexible microfabricated devices that use thin film...

Micro-Particle Image Velocimetry (μPIV) measurements often suffer from poor image quality because of volume illumination effects, out of focus particles, and low seeding densities. As a result, measurements are typically ensemble averaged in time to improve the signal-to-noise ratio (SNR) of the resulting cross correlations. To achieve reliable, ti...

Lipid bilayers are biomembranes common to cellular life and constitute a continuous barrier between cells and their environment. Understanding the interaction of nanoparticles with lipid bilayers is an important step toward predicting subsequent biological effects. In this study, we assessed the affinity of functionalized gold nanoparticles (Au NPs...

Bimetallic particles propel themselves through aqueous solutions by harvesting chemical energy from hydrogen peroxide fuel and converting it to fluid motion through reaction-induced charge auto-electrophoresis. We present a scaling analysis and computational simulations that describe the physics underlying the locomotion of these particles. The mod...

Water and energy production and demand are interconnected. Polymer electrolyte membrane fuel cells (PEMFCs) are devices that produce water while they generate power using hydrogen as a fuel. Herein, a lab-scale PEMFC was operated under variable experimental conditions, such as membrane chemical composition, operating temperature, operating current...

This paper presents a radial frit geometry electroosmotic pump with a soft, semi-permeable gas venting membrane top. Radial pumps exhibit more than three times the average open flow rate per applied voltage and four times the average flow rate per sourced power than linear pumps for a given pump package volume. The radial pump can operate over a 16...

Biological membranes are one of the important interfaces between cells and pollutants. Many polar and hydrophobic chemicals can accumulate within these membranes. For this reason, artificial biological membranes are appealing surrogates to complex organisms for assessing the bioaccumulation potential of engineered nanomaterials (ENMs). To our knowl...

Synthetic nanomotors, like their biological counterparts, propel themselves through aqueous solutions by harvesting chemical energy from their local environment and converting it to mechanical energy. We study bimetallic rod-shaped particles which move autonomously by catalytically decomposing hydrogen peroxide to oxygen and water. We present a sca...

The goal of this study was to examine the effects of pH and ionic strength on octanol-water distribution of five model engineered nanomaterials. Distribution experiments resulted in a spectrum of three broadly classified scenarios: distribution in the aqueous phase, distribution in the octanol, and distribution into the octanol-water interface. Two...

Fuel cells are devices capable of producing both energy and clean water. Here the concept of using hydrogen as a carrier of water and energy is explored by studying the quality of water produced by two modern commercial fuel cells, a 1 kW residential-scale polymer electrolyte membrane fuel cell (PEMFC) and a larger 300 kW molten carbonate fuel cell...

A membraneless microfluidic fuel cell stack architecture is presented that reuses reactants from one cell to a subsequent one, analogous to PEMFC stacks. On-chip reactant reuse improves fuel utilization and power densities relative to single cells. The reactants flow separately through porous electrodes and interface with a non-reacting and conduct...

A diagnostic platform for measuring three dimensional velocity fields in whole microscopic volumes is presented. The imaging system is based on Nipkow spinning disk confocal microscopy. The confocal system provides optical sectioning using pinhole spatial filtering which rejects light originating from out of focus objects. Volumetric scanning is ob...

Nanosilver has become one of the most widely used nanomaterials in consumer products because of its antimicrobial properties. Public concern over the potential adverse effects of nanosilver's environmental release has prompted discussion of federal regulation. In this paper, we assess several classes of consumer products for their silver content an...

A counter flow membraneless microfluidic fuel cell is presented, where a non-reacting electrolyte separates the reacting streams. In this fuel cell design, vanadium reactants flow through porous carbon electrocatalysts. A sulfuric acid stream is introduced in the gap between the electrodes and diverts the reactants to opposite and independent outle...

An investigation of two-frame micro particle image velocimetry (µPIV) correlations is presented that utilizes a high-speed, spinning disk confocal micro particle image velocimetry (SDµPIV) system. The system uses Nipkow disk confocal epifluorescence microscopy and a high-speed camera to capture unsteady microscale flows using two-frame cross correl...

Catalytic bimetallic nanomotors can swim at 100 body lengths per second as well as pick up, haul, and release micrometer-scale cargo. The electrokinetic locomotion of bimetallic nanomotors is driven by the electrocatalytic decomposition of hydrogen peroxide. The motors are typically fabricated by electrodeposition-based template synthesis technique...

Bimetallic rod-shaped nanomotors swim autonomously in hydrogen peroxide solutions. Here, we present a scaling analysis, computational simulations, and experimental data that show that the nanomotor locomotion is driven by fluid slip around the nanomotor surface due to electrical body forces. The body forces are generated by a coupling of charge den...

We report a diverse set of coherent fluid flow instabilities, particle patterns, and traveling waves that develop when an ac electric field is applied to nondilute colloidal dispersions with volume fractions that span 3 orders of magnitude. Novel observed phenomena include the following: vortices with steady and unsteady axes of rotation, unsteady...

Controlled motion of synthetic nanoscale motors may represent a major step towards the development of practical nanomachines and autonomous microsystems. Bimetallic nanorods can autonomously propel themselves at hundred of body lengths per second through aqueous solutions by using hydrogen peroxide as a fuel. The magnetic and chemical controlled mo...

The existence of electrokinetically-driven, traveling waves in colloidal dispersions is presented. A non-dilute colloidal dispersion of 2 micron polystyrene microspheres are exposed to an ac electric field. Traveling waves consist of alternating regions of compressed and rarefied particle volume fraction that propagate through the dispersion parall...

Bimetallic nanorods can autonomously propel themselves through aqueous solutions by using hydrogen peroxide as a fuel. Several physical arguments have been proposed to describe the physics underlying the chemically-powered locomotion of these synthetic nanomotors, but there is no accepted or detailed theory on the propulsion mechanism. A computatio...

A high speed micro particle imaging velocimetry system based on a spinning disk confocal microscope is presented. The confocal system uses a spinning disk with a series of pinholes arranged in an Archimedes spiral to optically section the sample, rejecting light originating from out of focus particles. Unsteady flows require two frame cross correla...

An electrochemically-controlled movement of catalytic nanomotors, including a cyclic 'on/off' activation of the nanomotor motion and a fine speed control, is illustrated.

In a future hydrogen economy, harvesting water from H(2) fuel cells and other devices should be considered as a by-product of their operation. We hypothesize that the water quality produced by modern fuel cells is higher than typical tap waters and complies with US Environmental Protection Agency (USEPA) regulations. Water samples were collected fr...

We present experimental measurements of electromigration current through a single cylindrical nanopore. A single cylindrical nanopore with 175 nm diameter was fabricated in silicon in series with two micropores with 2 and 100 microm diameters. Thick electrical double layers (EDLs) (kappa a approximately 1) exhibit current rectification due to asymm...

A method of quantifying equilibrium reactions in a microchannel using a fluorometric reaction of Fluo-4 and Ca2+ ions is presented. Under the proper conditions, equilibrium reactions can be used to quantify fluid mixing without the challenges associated with constituent mixing measures such as limited imaging spatial resolution and viewing angle co...

A microfluidic method to rapidly measure the octanol-water partition coefficient in thousands of individual picoliter drops is described. A T-junction microfluidic chip is used to generate a segmented flow of monodisperse, fluorescein-laden water in octanol carrier fluid. The partitioning of individual drops reaches equilibrium in less than 2 s. Ep...

This paper is a critical review of how the fluid properties (e.g., density, viscosity, conductivity, and permittivity) and behaviors (e.g., electrophoretic motion, electrokinetic aggregation, chaining, and instabilities) depend on colloid volume fraction. The review focuses on electrokinetic flows in aqueous solutions with suspensions on the order...

An experimental investigation of electrokinetic instabilities (EKIs) of non-dilute colloidal suspensions in microchannels is presented. The addition of charged colloidal particles to a solution can alter the solution's electrical conductivity and permittivity as well as the average particle electrophoretic mobility. In this work, a colloidal (500 n...

Over the past five years there has been a growing interest in the interactions between engineered nanomaterials and cellular constituents. Quantitative measures of nanomaterial bioavailability and toxicity must be made so that the impact of nanotechnology on human health and the environment can be addressed. Recent research focuses on either collec...

We present the experimental measurements of electromigration current through a single cylindrical nanopores. A cylindrical nanopore with ~175 nm diameter was fabricated using standard clean-room semiconductor processing techniques. The fabricated nanopore exhibits electromigration rectification with low concentration solutions (100 μM KCl) and near...

A novel convective flow membraneless microfluidic fuel cell with porous disk electrodes is described. In this fuel cell design, the fuel flows radially outward through a thin disk shaped anode and across a gap to a ring shaped cathode. An oxidant is introduced into the gap between anode and cathode and advects radially outward to the cathode. This...

In non-dilute colloidal suspensions, gradients in particle volume fraction result in gradients in electrical conductivity and permittivity. An externally applied electric field couples with gradients in electrical conductivity and permittivity and, under some conditions, can result in electric body forces that drive the flow unstable forming vortic...

Focused ion beam milling is used to fabricate micron and submicron scale patterns in sintered silica colloidal crystal films. Rectangular cavities with both solid and porous boundaries, fluidic channels, and isolation of a small number of packed spheres are patterned. The ion beam can pattern sintered films of individual submicron size spheres and...

Mechanical behavior of cells is primarily governed by the cytoskeleton (CSK), a remarkable system of filaments consisting of microtubules, actin filaments and intermediate filaments. This system defines the shape and bulk mechanical properties of the cell. In order to understand how the CSK network influences the mechanical behavior of living cells...

We illustrate the use of catalytic nanowire motors for directional motion and microscale transport of cargo within microfluidic channel networks. The CNT-based synthetic nanomotor can propel a large cargo load at high speeds through predetermined paths and junctions of the microchannel network. The magnetic properties of the nickel-containing nanom...

In this work, nanopores are formed in lipid (DOPC:DOPE) membranes suspended across 150 micron apertures by oligomeric aggregation of 12 nm diameter CdSe quantum dots. The bilayer and quantum dot nanopores are simultaneously characterized by low noise electrical current monitoring and epifluorescence microscopy. Suspended lipid bilayers form high re...

This paper investigates a hydrodynamic particle separation technique that employs pinching of particles to a narrow microchannel. The particles are subject to a sudden expansion which results in a size-based particle separation transverse to the flow direction. The separation resolution and particle dispersion are measured using epifluorescence mic...

Researchers came together for the 24th Annual Meeting of the American Electrophoresis Society (AES), which was held November 4-9, 2007, at the Salt Palace Convention Center in Salt Lake City, UT, U.S.A. The Annual AES meeting is held in conjunction with the annual meeting of the American Institute of Chemical Engineers (AIChE). This year's meeting...

We present experimental investigations of electroosmotic pumping using porous borosilicate glass and various low ion density liquids. The working liquids were deionized water, deuterium oxide (heavy water), methanol, acetone, acetonitrile and a 1 mM sodium borate buffer as a control. We measured ionic conductivity and, as a useful comparative refer...

Nanoscale apertures that provide a fluidic path between two reservoirs can be used for numerous applications. These applications include patch-clamp type measurements, Coulter counting and molecular studies. For Coulter counting of nanometer-sized analytes, we have developed a process capable of reproducibly fabricating cylindrical apertures in a s...

Direct current operation of electroosmotic pumps consumes water and generates electrolysis gas bubbles that can block the working electrode and build up pressure in the pump housing. The formation of the electrolysis gases can degrade pump performance and can lead to failure. Although catalysts have been used to recombine the electrolytic gases, cu...

An experimental investigation of electrokinetic particle aggregation and flow instabilities of non-dilute colloidal suspensions in microfabricated channels is presented. The addition of charged colloidal particles can alter the solution's conductivity, permittivity as well as the average particle electrophoretic mobility. In this work, a colloid vo...

Cylindrical solid-state nanopores with 40 nm diameter were fabricated in silicon-on-insulator substrates using standard cleanroom semiconductor processing techniques. Here we report on a fabrication sequence which consistently produced robust nanopores with control over the final diameter. The electrolyte concentration dependence of ion transport t...

Electric fields coupled with ionic conductivity gradients generates charge density in the bulk fluid which can result in electrokinetic instabilities (EKI). Electrokinetic (EK) flow with conductivity gradients become unstable when the electroviscous stretching and folding of conductivity interfaces grows faster than the dissipative effect of molecu...

Recent experimental and numerical investigations on proton exchange membrane fuel cells (PEMFCs) emphasize water management as a critical factor in the design of robust, high efficiency systems. Although various water management strategies have been proposed, water is still typically removed by pumping air into cathode channels at flow rates signif...

This paper presents experimental data on the effects of varying ambient temperature (10–40 °C) and relative humidity (20–80%) on the operation of a free-breathing fuel cell operated on dry-hydrogen in dead ended mode. We visualize the natural convection plume around the cathode using shadowgraphy, measure the gas diffusion layer (GDL) surface tempe...

N-type porous silicon can be used to realize electroosmotic pumps with high flow rates per applied potential difference. The porosity and pore size of porous silicon membranes can be tuned, the pore geometry has near-unity tortuosity, and membranes can be made thin and with integrated support structures. The size of hexagonally packed pores is modi...

We present experimental investigations of porous glass electroosmotic pumping of methanol/water mixture to study the feasibility of electroosmotic pump applications for direct methanol fuel cells. We first measure electroosmotic mobility of deionized water and pure methanol and evaluate pump pressure, flow rate, and current.

We have developed proton exchange membrane fuel cells (PEMFCs) with integrated planar electroosmotic (EO) pumping structures that actively remove liquid water from cathode flow channels. EO pumps have no moving parts, scale appropriately with fuel cells, can operate across a wide range of conditions, and consume a small fraction of fuel cell power....