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Monitoring different adherent cell subpopulations sizes and their environment under fluid shear stress conditions with a microfluidic impedance platform.

A study of like-charged, bimodal colloidal suspensions was conducted in microgravity aboard the International Space Station as part of NASA's Advanced Colloids Experiments-Heated-2 (ACE-H-2) experiments. Samples comprised of silsesquioxane microparticles (600 nm) and zirconia nanoparticles (5–15 nm) in 1.5 pH nitric acid were mixed and allowed to agglomerate over time while being imaged with NASA's Light Microscopy Module (LMM). The samples contained 1% of microparticles with varying concentrations of nanoparticles in 0.1%, 0.055%, and 0.01% by volume. Digital images were captured periodically by the LMM over 12 days. Image analysis, including cluster size and distribution, was performed in Python using the “Colloidspy” package. The study found that cluster size had increased over time in at least seven of nine samples, but two samples exhibited nonlinear growth rates, while others showed very slow growth with cluster sizes two orders of magnitude greater than the free microparticles. We hypothesize that all samples experienced nonlinear growth, but early transient effects after mixing were missed due to timing limitations in image acquisition. Transport limitations of clusters in these systems may have dominated agglomeration behavior in microgravity, despite the samples being thermodynamically unstable, but more study is required.

Trapping, sorting, transportation, and manipulation of synthetic microparticles and biological cells enable investigations in their behavior and properties. Microfluidic techniques like rapid electrokinetic patterning (REP) provide a non-invasive means to probe into the nature of these micro and nanoparticles. The opto-electrically induced nature of a REP micro vortex allows tuning of the trap characteristics in real-time. In this work, we studied the effects of transient optical heating on the induced electrothermal vortex using micro-particle image velocimetry (μ-PIV) and computational modeling. A near infra-red (980 nm) laser beam was focused on a colloidal suspension of 1 μm polystyrene beads sandwiched between two parallel-plate electrodes. The electrodes were subjected to an AC current. The laser spot was scanned back-and-forth in a line, at different frequencies, to create the transient vortex. This phenomenon was also studied with a computational model made using COMSOL Multiphysics. We visualize fluid flow in custom-shaped REP traps by superposing multiple axisymmetric (spot) vortices and discuss the limitations of using superposition in dynamically changing traps.

This study used impedance spectroscopy measurements to extract the electrical properties of phytoplankton cells in suspension. Experimental measurements were acquired, and the single-shell model was applied to extract the specific membrane capacitance, cytoplasm permittivity, and conductivity of assumingly spherical cells in suspension utilizing Maxwell’s mixture theory of a controlled volume fraction of cells. The impedance of suspensions of algae was measured at different frequencies ranging from 3 kHz to 10 MHz and impedance values were compared to investigate differences between two types of cells by characterizing their change in cytoplasm permittivity and specific membrane capacitance. Differentiation between healthy control and nitrogen-depleted cultured algae was attempted. The extracted specific membrane capacitances of Chlamydomonas and Selenastrum were 15.5 ± 3.6 and 40.6 ± 12.6 mF m− 2 respectively. Successful differentiation based on the specific membrane capacitance of different algae species was achieved. However, no significant difference was noticed between nitrogen-abundant and nitrogen-depleted cultures.

Isomotive dielectrophoresis (isoDEP) is a unique electric field such that the gradient of the field-squared ([Formula: see text]) is constant, resulting a uniform dielectrophoretic force. The current status of isoDEP is presented in this review, and we will highlight the progress that has been achieved over the past 60 years in various avenues of isoDEP since H.A. Pohl initially described its premise. This article will discuss its applications and describe the various configurations of generating an isomotive force. Since H.A. Pohl introduced the theory of isoDEP, numerous authors have implemented isoDEP as a tool for the manipulation, sorting, separation, and characterization of polarizable particles without the need for biochemical labels or other bioengineered tagging. The growing field of microfluidics and electrokinetics has renewed interest in isoDEP, particularly for analytical characterization or separation of particles. Recent work has demonstrated that isoDEP can address some unmet needs for biomedical applications including single-cell analysis; moreover, advances in throughput as well as combining characterization and separation simultaneously will add significant value to isoDEP.

Colloidal particles like polystyrene beads and metallic micro and nanoparticles are known to assemble in crystal-like structures near an electrode surface under both DC and AC electric fields. Various studies have shown that this self-assembly is governed by a balance between an attractive electrohydrodynamic (EHD) force and an induced dipole-dipole repulsion (Trau et al., 1997). The EHD force originates from electrolyte flow caused by interaction between the electric field and the polarized double layers of both the particles and the electrode surface. The particles are found to either aggregate or repel from each other on application of electric field depending on the mobility of the ions in the electrolyte (Woehl et al., 2014). The particle motion in the electrode plane is studied well under various conditions however, not as many references are available in the literature that discuss the effects of the AC electric field on their out-of-plane motion, especially at high frequencies (>10 kHz). Haughey and Earnshaw (1998), and Fagan et al. (2005) have studied the particle motion perpendicular to the electrode plane and their average height from the electrode mostly in presence of DC or low frequency AC (10 kHz) electric field on the particles’ motion perpendicular to the electrode plane.

Hypothesis Self-assembled colloidal mobility out of a non-equilibrium system can depend on many external and interparticle forces including hydrodynamic forces. While the driving forces guiding colloidal suspension, translation and self-assembly are different and unique, hydrodynamic forces are always present and can significantly influence particle motion. Unfortunately, these interparticle hydrodynamic interactions are typically overlooked. Experiments Here, we studied the collective behavior of colloidal particles (4.0 µm PMMA), located near the solid surface in a fluid medium confined in a cylindrical cell (3.0 mm diameter, 0.25 mm height) which was rotated vertically at a low rotational speed (20 rpm). The observed colloidal behavior was then validated through a Stokesian dynamics simulation where the concept of hydrodynamic contact force or lubrication interactions are avoided which is not physically intuitive and mathematically cumbersome. Rather, we adopted hard-sphere like colloidal collision or mobility model, while adopting other useful simplification and approximations. Findings Upon particles settling in a circular orbit, they hydrodynamically interact with each other and evolve in different structures depending on the pattern of gravity forces. Their agglomeration is a function of the applied rotation scheme, either forming colloidal clusters or lanes. While evolving into dynamic structures, colloids also laterally migrate away from the surface.

While similar in nature, the properties of silica and silsesquioxane are very different, but little is known about these differences. In this paper, functionalized silsesquioxane microparticles are synthesized by adapting the modified St\"ober method and post-functionalized with rhodamine-B. The as synthesized silsesquioxane particles are characterized by a variety of physical and chemical methods. The synthesized particles are amorphous and nonporous in nature and are less dense than silica. While silsesquioxane and silica have some similar physical properties from their siloxane core, the organic functional group of silsesquioxane and the one-half oxygen difference in its structure impact many other properties of these particles like their charging behavior in liquids. These differences not only allow for the ease surface modification as compared to that necessary to modify silica, but also the use in a variety of colloidal systems that due to pH or electrolyte concentrations may not be suitable for silica particles. Keywords: silsesquioxane, Stober method, density, morphology, zeta potential

Pediatric heart failure patients remain in critical need of a dedicated mechanical circulatory support (MCS) solution as development efforts for specific pediatric devices continue to fall behind those for the adult population. The Inspired Pediatric VAD is being developed as a pediatric specific MCS solution to provide up to 30-days of circulatory or respiratory support in a compact modular package that could allow for patient ambulation during treatment.Hydrodynamic performance (flows, pressures), impeller/rotor mechanical properties (torques, forces), and flow shear stress and residence time distributions of the latest design version, Inspired Pediatric VAD V3, were numerically predicted and investigated using computational fluid dynamics (CFD) software (SolidWorks Flow Simulator).Hydrodynamic performance was numerically predicted, indicating no change in flow and pressure head compared to the previous device design (V2), while displaying increased impeller/rotor torques and translation forces enabled by improved geometry. Shear stress and flow residence time volumetric distributions are presented over a range of pump rotational speeds and flow rates. At the lowest pump operating point (3000 RPM, 0.50 L/min, 75 mmHg), 79% of the pump volume was in the shear stress range of 0-10 Pa with1% of the volume in the critical range of 150-1000 Pa for blood damage. At higher speed and flow (5000 RPM, 3.50 L/min, 176 mmHg), 65% of the volume resided in the 0-10 Pa range compared to 2.3% at 150-1000 Pa.The initial computational characterization of the Inspired Pediatric VAD V3 is encouraging and future work will include device prototype testing in a mock circulatory loop and acute large animal model.

During the COVID19 pandemic, various investigations have been conducted to determine if personal protective equipment (PPE), and specifically N95 masks, can be decontaminated for reuse when unused equipment is not available. One method under investigation that may be particularly adaptable in lower resource communities is the use of heat and humidity for the de-activation of SARS-CoV-2. Food-warming cabinets (also known as holding cabinets) may reach applicable temperatures and thus the purpose of this study was to characterize the temperatures achieved in a typical food-warming cabinets that has been adapted for the de-activation of N95 masks. This paper provides a general description of how a food-warming cabinet operates and describes aspects that are important for heat de-activation including characterizing cyclical heating and temperature variations within the cabinet. The described experimental procedure could be used as a guide to characterize similar food-warming cabinets.

Power generation from offshore wind grew vastly in the last 20 years, whilst remaining a relatively young industry without installed technology reaching the end of its design life before advancements are made. Most of the technology of MV (medium voltage) array cable accessories are based on the more experienced land power distribution industry, which faces very different operating conditions and yet are still bound by the same design and test standards. Recently the industry has seen failures related to some “T-connector” terminations on array cables operating offshore at 33 kV, over multiple wind farms and differing cable and termination suppliers. Root cause analysis has been performed by the Authors on one of these windfarms where the main cause of failure was identified as the screen earthing connection within the terminations. As no test methods exist in the relevant international standards, a new current endurance test has been developed to determine the suitability of the installed T-connector earthing methodology, as well as alternative designs. It was found during analysis of the test results that the installed earthing design, although having passed the required short circuit testing to the relevant standards, was not suitable for the design life of the larger cable cross sections used in the project. Two alternative designs, although improved were also not deemed suitable. Two newly designed connections, based on established technology utilising a soldered connection and a mechanical connection, have however, been approved for use.

When a sessile droplet of a complex mixture evaporates, its nonvolatile components may deposit into various patterns. One such phenomena, the coffee ring effect, has been a topic of interest for several decades. Here, we identify what we believe to be a fascinating phenomenon of droplet pattern deposition for another well-known beverage-what we have termed a "whiskey web". Nanoscale agglomerates were generated in diluted American whiskeys (20-25% alcohol by volume), which later stratified as microwebs on the liquid-air interface during evaporation. The web's strandlike features result from monolayer collapse, and the resulting pattern is a function of the intrinsic molecular constituents of the whiskey. Data suggest that, for our conditions (diluted 1.0 μL drops evaporated on cleaned glass substrates), whiskey webs were unique to diluted American whiskey; however, similar structures were generated with other whiskeys under different conditions. Further, each product forms their own distinct pattern, demonstrating that this phenomenon could be used for sample analysis and counterfeit identification.

The dynamic manipulation and assembly of colloids enables the advancement of analytical techniques in biotechnology and the development of self-assembled materials. Rapid electrokinetic patterning (REP) is a hybrid optoelectrokinetic technique that simultaneously uses a laser illumination and a uniform AC electric field to yield programmable, dynamic, and non-invasive manipulation of colloidal particles. Since it was introduced, the technique has been applied to microengineering and biological research fields, showing its promising capabilities as a great tool for trapping, aggregating, translating, and sorting single and multiple micro- and nanoparticles, including bacteria. To effectively leverage and enhance these applications, this review paper will highlight its versatility and capability, including REP’s principles, governing physics, different experimental setups, fabrications, applications, and future prospects.

When a water-diluted droplet of American whiskey evaporates, it can leave behind a self-assembled web pattern not found in Scotch or brandy.

Two dielectrophoresis systems are introduced where the induced dielectrophoretic force is constant throughout the experimental region, resulting in uniform (isomotive) microparticle translation. Isomotive dielectrophoresis (isoDEP) is accomplished through a unique geometry where the gradient of the field-squared (∇Erms2) is constant, a characteristic that is otherwise highly nonuniform in traditional DEP platforms. The governing isoDEP equations were derived herein and applied to two different isoDEP prototypes: (i) one fabricated from deep reactive ion etching (DRIE) of a conductive silicon wafer (1-10 Ω-cm) whose patterned features served as electrodes and microchannel sidewalls simultaneously; (ii) a second where the electric field is applied lengthwise through a PDMS microchannel whose geometry follows a specific curvature. Both positive and negative dielectrophoresis was demonstrated with the isoDEP devices using silver-coated hollow glass spheres and polystyrene particles, respectively. Particle tracking was used to compare particle trajectory with the expected dielectrophoretic response; further, particle velocity was used to measure the Clausius-Mossotti factor of individual polystyrene particles (18-24.9 μm) in both devices with a value of -0.40 ± 0.063 (n = 110) and -0.48 ± 0.055 (n = 18) for the DRIE and PDMS isoDEP platforms, respectively. The isoDEP platform is capable of analyzing multiple particles simultaneously, providing greater throughput than traditional electrorotation platforms.

Isomotive dielectrophoresis (isoDEP) is a unique DEP geometrical configuration where the gradient of the field-squared ( ∇ E rms 2 ) is constant. IsoDEP analyzes polarizable particles based on their magnitude and direction of translation. Particle translation is a function of the polarizability of both the particles and suspending medium, the particles' size and shape, and the frequency of the electric field. However, other electrokinetics act on the particles simultaneously, including electrothermal hydrodynamics. Hence, to maximize the DEP force relative to over electrokinetic forces, design parameters such as microchannel geometry, fabrication materials, and applied electric field must be properly tuned. In this work, scaling law analyses were developed to derive design rules, relative to particle diameter, to reduce unwanted electrothermal hydrodynamics relative to DEP-induced particle translation. For a particle suspended in 10 mS/m media, if the channel width and height are below ten particle diameters, the electrothermal-driven flow is reduced by ∼500 times compared to a channel that is 250 particles diameters in width and height. Replacing glass with silicon as the device's underlying substrate for an insulative-based isoDEP reduces the electrothermal induced flow approximately 20 times less.

The evaporation of a drop of American whiskey leaves a characteristic web-like pattern that isn't observed in Scotch whisky and other distillates.

This manuscript describes the potentially significant role of interfacial tension in viral infection. Our hypothesis is based on evidence from drop coalescence hydrodynamics. A change in membrane tension can trigger fusion between the vesicle and cell such that genetic material, like viral RNA, can subsequently be transported to the cell interior. In other cases, RNA may reside near the cell membrane inside the cell, which could make their removal energetically unfavorable because of hydrodynamic interactions between membrane and RNA. Interfacial tension of the virus membrane can be modulated by temperature, among many other factors, of the mucosa layer. We discuss our hypothesis within the scope of recent SARS-CoV-2 studies where temperature-dependent membrane surface tension could be impacted through different atmospheric conditions, air conditioning systems, and the use of masks., Graphical abstract Membrane tension may define the deadliest virus infection. Md Mahmudur Rahman, Stuart J Williams.Unlabelled Image

Electrical impedance techniques have been used to characterize endothelium morphology, permeability, and motility in vitro. However, these impedance platforms have been limited to either static endothelium studies and/or induced laminar fluid flow at a constant, single shear stress value. In this work, we present a microfabricated impedance sensor for real-time, in vitro characterization of human umbilical vein endothelial cells (HUVECs) undergoing oscillatory hydrodynamic shear. Oscillatory shear was applied with an orbital shaker and the electrical impedance was measured by a microfabricated impedance chip with discrete electrodes positioned at radial locations of 0, 2.5, 5.0, 7.5, 10.0, and 12.5 mm from the center of the chip. Depending on their radial position within the circular orbital platform, HUVECs were exposed to shear values ranging between 0.6 and 6.71 dyne/cm(2) (according to numerical simulations) for 22 h. Impedance spectra were fit to an equivalent circuit model and the trans-endothelial resistance and monolayer's capacitance were extracted. Results demonstrated that, compared to measurements acquired before the onset of shear, cells at the center of the platform that experienced low steady shear stress (∼2.2 dyne/cm(2) ) had an average change in trans-endothelial resistance of 6.99 ± 4.06% and 1.78 ± 2.40% change in cell capacitance after 22 hours of shear exposure; cells near the periphery of the well (r = 12.5 mm) experienced transient shears (2.5-6.7 dyne/cm(2) ) and exhibited a greater change in trans-endothelial resistance (24.2 ± 10.8%) and cell capacitance (4.57 ± 5.39%). This study, demonstrates that the orbital shear platform provides a simple system that can capture and quantify the real-time cellular morphology as a result of induced shear stress. The orbital shear platform presented in this work, compared to traditional laminar platforms, subjects cells to more physiologically relevant oscillatory shear as well as exposes the sample to several shear values simultaneously. Biotechnol. Bioeng. 2016;113: 1336-1344. © 2015 Wiley Periodicals, Inc.

Non-contact manipulation methods capable of trapping and transporting swimming bacteria can significantly aid in chemotaxis studies. However, high swimming speed makes the trapping of these organisms an inherently challenging task. We demonstrate that an optoelectric technique, rapid electrokinetic patterning (REP), can effectively trap and manipulate Enterobacter aerogenes bacteria swimming at velocities greater than 20 μm s(-1). REP uses electro-orientation, laser-induced AC electrothermal flow, and particle-electrode interactions for capturing these cells. In contrast to trapping non-swimming bacteria and inert microspheres, we observe that electro-orientation is critical to the trapping of the swimming cells, since unaligned bacteria can swim faster than the radially inward electrothermal flow and escape the trap. By assessing the cell membrane integrity, we study the effect of REP trapping conditions, including optical radiation, laser-induced heating, and the electric field on cell viability. When applied individually, the optical radiation and laser-induced heating have negligible effect on cells. At the standard REP trapping conditions fewer than 2% of cells have a compromised membrane after four minutes. To our knowledge this is the first study detailing the effect of REP trapping on cell viability. The presented results provide a clear guideline on selecting suitable REP parameters for trapping living bacteria.

Coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was classified as a pandemic by the World Health Organization and has caused over 550,000 deaths worldwide as of July 2020. Accurate and scalable point-of-care devices would increase screening, diagnosis, and monitoring of COVID-19 patients. Here, we demonstrate rapid label-free electrochemical detection of SARS-CoV-2 antibodies using a commercially available impedance sensing platform. A 16-well plate containing sensing electrodes was pre-coated with receptor binding domain (RBD) of SARS-CoV-2 spike protein, and subsequently tested with samples of anti-SARS-CoV-2 monoclonal antibody CR3022 (0.1 μg/ml, 1.0 μg/ml, 10 μg/ml). Subsequent blinded testing was performed on six serum specimens taken from COVID-19 and non-COVID-19 patients (1:100 dilution factor). The platform was able to differentiate spikes in impedance measurements from a negative control (1% milk solution) for all CR3022 samples. Further, successful differentiation and detection of all positive clinical samples from negative control was achieved. Measured impedance values were consistent when compared to standard ELISA test results showing a strong correlation between them (R2=0.9). Detection occurs in less than five minutes and the well-based platform provides a simplified and familiar testing interface that can be readily adaptable for use in clinical settings., Highlights • Capacitive immunosensing of clinically relevant concentrations of SARS-CoV-2 antibodies. • Antigen/antibody association and dissociation occurs within few seconds. • Rapid, label free detection using commercially available equipment. • Impedance peaks correlated with CR3022 concentration levels and ELISA measurements.

Rapid electrokinetic patterning (REP) is an emerging optoelectric technique that takes advantage of laser-induced AC electrothermal flow and particle-electrode interactions to trap and translate particles. The electrothermal flow in REP is driven by the temperature rise induced by the laser absorption in the thin electrode layer. In previous REP applications 350-700 nm indium tin oxide (ITO) layers have been used as electrodes. In this study, we show that ITO is an inefficient electrode choice as more than 92% of the irradiated laser on the ITO electrodes is transmitted without absorption. Using theoretical, computational, and experimental approaches, we demonstrate that for a given laser power the temperature rise is controlled by both the electrode material and its thickness. A 25-nm thick Ti electrode creates an electrothermal flow of the same speed as a 700-nm thick ITO electrode while requiring only 14% of the laser power used by ITO. These results represent an important step in the design of low-cost portable REP systems by lowering the material cost and power consumption of the system.

Rapid electrokinetic patterning (REP) is a technique for creating self-assembled monolayers (SAMs) of spherical particles in a liquid medium, and dynamically controlling them though the simultaneous application of an electric field and optically induced temperature gradients. Previous work has investigated and characterized REP axisymmetric aggregations generated from a focus laser within a uniform electric field; work herein characterizes line-shaped particle assemblies derived from the application of a linearly scanned laser. The resulting aggregations of spherical polystyrene particles (1 μm) suspended in low-conductivity aqueous potassium chloride solution (KCl, 2.5 mS/m) resembled elliptical-shaped crystalline geometries. The mean particle-to-particle spacing within the aggregation remained greater than 1.5 diameters for experiments herein (6.5 Vrms , 30 kHz) due to dipole-dipole repulsive forces. Interparticle spacing demonstrated a linear relationship (1.6-2.1 μm) with increasing scanning lengths (up to 83 μm), decreased from 1.9 to 1.7 μm with increasing scanning frequency (0.38-16 Hz) for a 53 μm scan length, and decreased from 2.0 to 1.6 μm with increasing laser power (11.9-18.8 mW) for a 59 μm, 16 Hz laser scan.

This manuscript demonstrates an inexpensive method of fabricating 3D dielectrophoretic microfluidic devices using a milling machine equipped with a sub-millimeter end mill. Features were milled into a copperclad substrate, otherwise typically used for printed circuit boards. Milled electrodes themselves serve as walls of the microfluidic channel therefore delivering a stronger electric field throughout the depth of the microchannel compared to traditional, coplanar electrode designs. Dielectrophoretic particle trapping and concentration were demonstrated with 8 μm polystyrene beads at voltages no greater than 10 V. The method of fabrication will be discussed as well as advantages and challenges associated with this technique.

Late embryogenesis abundant (LEA) proteins are found in desiccation-tolerant species from all domains of life. Despite several decades of investigation, the molecular mechanisms by which LEA proteins confer desiccation tolerance are still unclear. In this study, dielectrophoresis (DEP) was used to determine the electrical properties of Drosophila melanogaster (Kc167) cells ectopically expressing LEA proteins from the anhydrobiotic brine shrimp, Artemia franciscana. Dielectrophoresis-based characterization data demonstrate that the expression of two different LEA proteins, AfrLEA3m and AfrLEA6, increases cytoplasmic conductivity of Kc167 cells to a similar extent above control values. The impact on cytoplasmic conductivity was surprising, given that the concentration of cytoplasmic ions is much higher than the concentrations of ectopically expressed proteins. The DEP data also supported previously reported data suggesting that AfrLEA3m can interact directly with membranes during water stress. This hypothesis was strengthened using scanning electron microscopy, where cells expressing AfrLEA3m were found to retain more circular morphology during desiccation, while control cells exhibited a larger variety of shapes in the desiccated state. These data demonstrate that DEP can be a powerful tool to investigate the role of LEA proteins in desiccation tolerance and may allow to characterize protein-membrane interactions in vivo, when direct observations are challenging.

Hydrodynamics of drop coalescence has been studied theoretically and numerically by solving the Navier Stokes equation considering a single fluid after the minimum bridge formation. Many experiments have been performed to document bridge growth over time with the use of high speed videography and electrical methods. However, internal fluid motion during coalescence has not been extensively studied, in part due to the spherical shape of the drops. This work observed overall fluid motion (except at the site of early coalescence) using particle image velocimetry for two-dimensional (sandwiched drop) coalescence. Fluid motion inside the bulk drops is inertial, and governing fluid flow in the bridge region is one dimensional. At the merging interface, incoming liquids join and coflow in the perpendicular direction. These observations were extended to a three-dimensional counterpart, and a scaling law was developed that was validated through experimentation. While flow in the bulk drops is inertial, the dominant resistance comes through a viscous effect in the merging interface region and at the lesser extent in the bridge region. Early dynamics of drop coalescence is dominated by the Ohnesorge number (Oh), and later dynamics are dependent on how drops are bounded.

This work demonstrates the use of thin film heaters to enhance electrothermal pumping in microfluidic systems. Thin film heating electrothermal pumping is more efficient than Joule heating alone. Numerical simulations of an asymmetric electrode array are performed to demonstrate the advantages of incorporating thin film heaters. This specific simulation shows that thin film heater electrothermal pumping provides approximately two and one-half times more volumetric flow than Joule heating alone for the same input power to both systems. In addition, external heating allows for electrothermal pumping to be applicable to low conductivity media.

Reliable and simple techniques for rapid assembly and patterning of colloid architectures advance the discovery and implementation of such nanomaterials. This work demonstrates rapid electrokinetic two-dimensional assembly of colloidal structures guided by the geometry of thin film heaters within a parallel-plate device. This system is designed to enable either independently addressable or massively parallel colloidal assembly. A combination of electrothermal hydrodynamics, particle-electrode, and particle-particle electrokinetic interactions governs their assembly. Concentration and patterning of structures are shown with 1.0 μm polystyrene particles and sorting between 1.0 μm and 2.0 μm particles is demonstrated.

In the path toward the realization of carbon nanotube (CNT)-driven electronics and sensors, the ability to precisely position CNTs at well-defined locations remains a significant roadblock. Highly complex CNT-based bottom–up structures can be synthesized if there is a method to accurately trap and place these nanotubes. In this study, we demonstrate that the rapid electrokinetic patterning (REP) technique can accomplish these tasks. By using laser-induced alternating current (AC) electrothermal flow and particle–electrode forces, REP can collect and maneuver a wide range of vertically aligned multiwalled CNTs (from a single nanotube to over 100 nanotubes) on an electrode surface. In addition, these trapped nanotubes can be electrophoretically deposited at any desired location onto the electrode surface. Apart from active control of the position of these deposited nanotubes, the number of CNTs in a REP trap can also be dynamically tuned by changing the AC frequency or by adjusting the concentration of the dispersed nanotubes. On the basis of a calculation of the stiffness of the REP trap, we found an upper limit of the manipulation speed, beyond which CNTs fall out of the REP trap. This peak manipulation speed is found to be dependent on the electrothermal flow velocity, which can be varied by changing the strength of the AC electric field. A technique for precisely positioning nanostructures could enable intricate electronic devices. Carbon nanotubes are hollow cylinders of carbon atoms with excellent electrical properties. However, they are difficult to manipulate due to their ultrasmall size. Steve Wereley from Purdue University in the United States and his colleagues used a laser beam and an electric field to align carbon nanotubes on the surface of an electrode. The team’s technique—known as rapid electrokinetic patterning—works by trapping and translating nanotubes that are suspended in water between two electrodes. Laser light is used to heat a small volume of the liquid, which changes its permittivity and electrical conductivity. When combined with an electric field between the electrodes, this generates vortices that can trap single or multiple nanotubes. The nanotubes can then be dynamically positioned by moving the laser beam.

Optically-based lab-on-a-chip systems have the distinct advantage of being dynamically controlled in real time, providing reconfigurable operations that can be tuned to perform a variety of tasks. This manuscript demonstrates the concentration of liquid-suspended microparticles using a focused near-infrared laser (980 nm) and a parallel-plate electrode system. The parallel-plate electrodes consisted of an indium tin oxide-coated coverslip and a gold-coated glass substrate. When the laser was applied at 36 mW, the indium tin oxide surface is locally heated creating sharp temperature gradients on the order of 0.07(o) C/μm. When an AC field was applied, electrothermal hydrodynamic forces generated microfluidic vortices. At an AC frequency of 40 kHz, the optically controlled electro-hydrodynamics aggregated colloids at the center of fluid motion on the surface of the indium tin oxide coverslip. The nature of colloid aggregation, translation, and patterning was explored when the translational velocity of the laser spot was varied. This manuscript describes the design of the laser scanning system using commercially available components and the fabrication of the parallel-plate chip. The effect that the laser scanning rate has on the heat transfer, fluid velocity, and colloid aggregation is discussed.

We study the three-dimensional fluid transport in an electrothermal microvortex (EMV), by using wavefront deformation particle-tracking velocimetry (PTV) developed at Universitat der Bundeswehr Munchen. By using a cylindrical lens in conjunction with a microscope objective lens, systematic wavefront deformations in the particle images are created. The particles are observed by a single camera and appear as ellipses. The elliptical nature of the particle images encodes out-of-plane information regarding the particle’s position. This new technique is ideally suited for measuring transport in the EMV and provides full three-dimensional, time-resolved particle trajectories with Lagrangian velocity and acceleration. Measurements reveal the toroidal nature of the EMV and the experimentally obtained velocities are used to validate a simplistic model, which describes the interaction between the applied laser illumination and the microfluidic device. The model allows one to conduct numerical simulations of the complex fluid transport in the EMV.

The development and analysis of the performance of microfluidic components for lab-on-a-chip devices are becoming increasingly important because microfluidic applications are continuing to expand in the fields of biology, nanotechnology, and manufacturing. Therefore, the characterization of fluid behavior at the scales of micro- and nanometer levels is essential. A variety of microfluidic velocimetry techniques like micron-resolution Particle Image Velocimetry (μPIV), particle-tracking velocimetry (PTV), and others have been developed to characterize such microfluidic systems with spatial resolutions on the order of micrometers or less. This article discusses the fundamentals of established velocimetry techniques as well as the technical applications found in literature.

We study a recently demonstrated AC electrokinetic technique for manipulation and concentration of colloidal particles on an electrode surface. The technique uses indium tin oxide (ITO)-based parallel-plate electrodes on which highly localized infrared (1064 nm) laser illumination is shone. We show that the highly localized laser illumination leads to a highly nonuniform heating of the electrode substrate, which in turn drives an electrothermal microvortex resulting in a rapid transport of particles toward the illuminated site. Hundreds of polystyrene particles, with diameters ranging from 2.0 to 0.1 microm, suspended in a low conductivity solution (2.0 mS/m) could be aggregated at selected locations on the electrode by activating the laser illumination at suitable AC frequencies. Subsequent deactivation of the laser illumination causes the particles to scatter, and we explore this dynamical behavior for 1.0 microm particles using Delaunay tessellations and high-speed videography. We establish that drag from the electrothermal microvortex acts against a repulsive force, which decreases with increasing AC frequency, to create stable particle clusters. Moreover, experimentally we show that this particle capturing technique can be characterized by a critical frequency: a frequency at which the captured colloidal particle cluster becomes unstable and particles are carried away into the bulk by the electrothermal microvortex. This critical frequency increases with decreasing particle diameter for similar particles. For 0.1 microm particles, comparison of aggregation at different AC frequencies is achieved by the comparison of fluorescent intensity profiles of the aggregations.

Capsule The population of Red‐throated Divers in Britain increased between 1994 and 2006. Aim To determine the population size and distribution of Red‐throated Divers in Britain for comparison with the previous national survey in 1994. Methods All freshwater bodies in Shetland, Orkney and two Special Protection Areas (SPAs) in the Hebrides were censused for Red‐throated Divers. A stratified sample of 5‐km squares was surveyed throughout the rest of the range. Two visits were made to all suitable habitats, at least 2 weeks apart, between 15 May and 31 July. Results The British breeding population of Red‐throated Divers was estimated to be 1143 breeding pairs, although around 12% of adults recorded as non‐breeding may actually have bred. Thus, a corrected estimate was calculated giving 1255 (95% CI 1014–1551) pairs. The total population of adults was estimated to be 4146 (95% CI 3430–4992). Shetland held 33% and the Outer Hebrides 26% of the breeding population. The estimated breeding population and total p...

Rapid electrokinetic patterning (REP) is an emerging optoelectric technique that takes advantage of laser-induced AC electrothermal flow and particle-electrode interactions to trap and translate particles. The electrothermal flow in REP is driven by the temperature rise induced by the laser absorption in the thin electrode layer. In previous REP applications 350-700 nm indium tin oxide (ITO) layers have been used as electrodes. In this study, we show that ITO is an inefficient electrode choice as more than 92% of the irradiated laser on the ITO electrodes is transmitted without absorption. Using theoretical, computational, and experimental approaches, we demonstrate that for a given laser power the temperature rise is controlled by both the electrode material and its thickness. A 25-nm thick Ti electrode creates an electrothermal flow of the same speed as a 700-nm thick ITO electrode while requiring only 14% of the laser power used by ITO. These results represent an important step in the design of low-cost portable REP systems by lowering the material cost and power consumption of the system.

Electrical impedance techniques have been used to characterize endothelium morphology, permeability, and motility in vitro. However, these impedance platforms have been limited to either static endothelium studies and/or induced laminar fluid flow at a constant, single shear stress value. In this work, we present a microfabricated impedance sensor for real-time, in vitro characterization of human umbilical vein endothelial cells (HUVECs) undergoing oscillatory hydrodynamic shear. Oscillatory shear was applied with an orbital shaker and the electrical impedance was measured by a microfabricated impedance chip with discrete electrodes positioned at radial locations of 0, 2.5, 5.0, 7.5, 10.0, and 12.5 mm from the center of the chip. Depending on their radial position within the circular orbital platform, HUVECs were exposed to shear values ranging between 0.6 and 6.71 dyne/cm(2) (according to numerical simulations) for 22 h. Impedance spectra were fit to an equivalent circuit model and the trans-endothelial resistance and monolayer's capacitance were extracted. Results demonstrated that, compared to measurements acquired before the onset of shear, cells at the center of the platform that experienced low steady shear stress (∼2.2 dyne/cm(2) ) had an average change in trans-endothelial resistance of 6.99 ± 4.06% and 1.78 ± 2.40% change in cell capacitance after 22 hours of shear exposure; cells near the periphery of the well (r = 12.5 mm) experienced transient shears (2.5-6.7 dyne/cm(2) ) and exhibited a greater change in trans-endothelial resistance (24.2 ± 10.8%) and cell capacitance (4.57 ± 5.39%). This study, demonstrates that the orbital shear platform provides a simple system that can capture and quantify the real-time cellular morphology as a result of induced shear stress. The orbital shear platform presented in this work, compared to traditional laminar platforms, subjects cells to more physiologically relevant oscillatory shear as well as exposes the sample to several shear values simultaneously. Biotechnol. Bioeng. 2016;113: 1336-1344. © 2015 Wiley Periodicals, Inc.

We report the results of a study characterizing the behavior of colloid aggregations under manipulation of a technique known as Rapid Electrokinetic Patterning (REP) – this technique is capable of dynamically manipulating the crystallinity of 2D colloid aggregations, potentially enabling dynamically tunable photonic crystals. Herein, aggregations of spherical polystyrene particles 1.0 μm in diameter suspended in a low conductivity aqueous solution were collected at the surface of an indium-tin oxide coated glass slide. The uniform AC field coupled with laser-induced heating produced electrothermal hydrodynamics which is responsible for the self-assembly characteristics of the planar colloidal aggregation. REP was characterized experimentally by analyzing the mutual particle spacing within the aggregation as a function of the AC signal and laser power. Numerical simulations justified the assumption that the primary forces responsible for colloidal patterning herein are Stokes drag forces and dipole–dipole repulsive forces.

Interdigitated electrodes are used in electrokinetic lab-on-a-chip devices for dielectrophoretic trapping and characterization of suspended particles, as well as the production of field-induced fluid flow via AC electroosomosis and electrothermal mechanisms. However, the optimum design for dielectrophoresis, that if symmetrical electrodes, cannot induce bulk electrohydrodynamic pumping. In addition, the mechanism of intrinsic electrothermal pumping is affected by the properties of the fluid, with thermal fields being generated by Joule Heating. This work demonstrates the incorporation of an underlying thin film heater, electrically isolated from the interdigitated electrodes by an insulator layer, to enhance bulk electrothermal pumping. The use of integrated heaters allows the thermal field generation to be controlled independently of the electric field. Numerical simulations are performed to demonstrate the importance of geometrical arrangement of the heater with respect to the interdigitated electrodes, as well as electrode size, spacing, and arrangement. The optimization of such a system is a careful balance between electrokinetics, heat transfer, and fluid dynamics. The heater location and electrode spacing influence the rate of electrothermal pumping significantly more than electrode width and insulator layer thickness. This demonstration will aid in the development of microfluidic electrokinetic systems that want to utilize the advantages associated with electrothermal pumping while simultaneously applying other lab-on-a-chip electrokinetics like dielectrophoresis.

Technologies that can enable concentration of low-abundance biomarkers are essential for early diagnosis of diseases. In this study, an optoelectrokinetic technique, termed Rapid Electrokinetic Patterning (REP), was used to enable dynamic particle manipulation in bead-based bioassays. Various manipulation capabilities, such as micro/nanoparticle aggregation, translation, sorting and patterning, were developed. The technique allows for versatile multi-parameter (voltage, light intensity and frequency) based modulation and dynamically addressable manipulation with simple device fabrication. Signal enhancement of a bead-based bioassay was demonstrated using dilute biotin–fluorescein isothiocyanate (FITC) solutions mixed with streptavidin-conjugated particles and rapidly concentrated with the technique. As compared with a conventional ELISA reader, the REP-enabled detection achieved a minimal readout of 3.87 nM, which was a 100-fold improvement in sensitivity. The multi-functional platform provides an effective measure to enhance detection levels in more bead-based bioassays.

Methods are described for the preparation of a range of N,N,N′,N′-tetraalkylformamidinium and N,N-dialkyliminium ions 4–20 as anhydrous salts for use as precursors to diamino- and amino-carbenes. These methods include a novel method involving nucleophilic addition to formamides followed by trapping with electrophiles such as triflic anhydride, various methods of formamide activation, exchange reactions involving orthoesters and the transamination of amidinium salts, and alkylation methods.

The temperature induced aggregation phenomena of a series of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymers (poloxamers) were investigated using dye incorporation UV spectroscopy, over a range of mass concentrations (0.1–15 mg ml −1 ). Initial experiments were performed using two different dyes (1,6-diphenyl-1,3,5-hexatriene (DPH) and I 2 ) so that the performance of each indicator for studying poloxamer aggregation could be determined. Subsequently, the onset temperatures ( T o ) and temperature maxima ( T m ) for the aggregation processes of 19 poloxamers were determined, using I 2 as an indicator. The aggregation temperature was observed to be dependent on both molecular mass and solution concentration for polymers comprising the same percent PEO, the aggregation temperature decreasing with increasing mass and/or increasing concentration.