Function Of Electric Field Strength Research Articles

DYNAMIC SELF-ASSEMBLY IN E.COLI BACTERIA SUSPENSION

We experimentally investigate self-assembly in bacteria suspension under low frequency alternating electric field. We observe the emergence of electric field-induced bacterial clusters as a function of electric field strength and bacterial concentrations. Above the electric critical field, bacterial cell self-organize into clusters, with further increase in field strength or bacteria concentration, a second critical point is reached, where 3D out of equilibrium structures are formed. Our findings demonstrates that the self-assembly of microswimmers can be controlled via external electric field. The observed cluster size dynamic equilibrium is in contrast with the features of cluster dynamics observed in cancer cells driven by adhesion where the cluster size distribution never reaches dynamic equilibrium. These results can offer a new pathway to self-organize living cells in biomaterials

Simulation Study on Safe Distance between Crane Boom and High-Voltage Line Based on Electric Field Intensity

Aiming at the safety accident caused by the close distance between the crane arm and the high-voltage line when the crane is working near the high-voltage transmission line, this paper proposes a simulation model of the electric field intensity distribution of the high-voltage transmission line. First, through the simplification and equivalent treatment of the high-voltage line, the simulation modeling, and analysis of the electric field around the high-voltage line are carried out. Then, the theory of solving the electric field intensity of any point around the high-voltage line based on the charge simulation method is deduced, and the conclusion that the electric field intensity at the equal distance of the high-voltage line is approximately equal is obtained. Furthermore, the influence of the crane on the electric field strength of a high-voltage line is analyzed, and the linear correction function of electric field strength is obtained. Based on the research in this paper, the field strength sensor can be used to obtain the value of the electric field strength, calculate the distance between the crane and the high-voltage line, and make a safety warning response. The simulation results verify the feasibility and effectiveness of the proposed model and method.

Fabrication and testing of functionalized multi-walled carbon nanotubes/deproteinized natural rubber composites for bending actuation under electric field

Compliant electrodes (CEs) were prepared from deproteinized natural rubber (DPNR) and multi-walled carbon nanotubes (MWCNTs) using Triton X-100 as a dispersing agent. Dielectric elastomers (DEs) were fabricated, from the DPNR incorporated with functionalized MWCNTs as a high dielectric constant filler, by film casting and the UV-curing process. The effect of MWCNT concentrations on mechanical and electrical properties of the CEs and DEs were individually examined. The defection responses and the dielectrophoresis forces of DEs and DEs attached on one side with CEs (DEs/CEs) were investigated as functions of electric field strength. The 5% v/v MWCNTs composite (CE_5) showed the highest conductivity of 19.7 S/cm and was subsequently used in the DEs/CEs bending experiment. The 2.5 phr of functionalized MWCNTs composite (DE_2.5) showed the highest dielectric constant of 15.4, but a relatively low bending actuation due to its initial high rigidity. The DE_1/CE_5 bilayer composite possessed the highest bending actuation, namely the largest bending distance and the dielectrophoresis force, presumably from the additional polarizations within CE_5 and the interactions with DE_5.

Ferroelectric Smectic Liquid Crystals as Electrocaloric Materials

The 1980s saw the development of ferroelectric chiral smectic C (SmC*) liquid crystals (FLCs) with a clear focus on their application in fast electro-optic devices. However, as the only known fluid ferroelectric materials, they also have potential in other applications, one of which is in heat-exchange devices based on the electrocaloric effect. In particular, ferroelectric liquid crystals can be both the electrocaloric material and the heat exchanging fluid in an electrocaloric device, significantly simplifying some of the design constraints associated with solid dielectrics. In this paper, we consider the electrocaloric potential of three SmC* ferroelectric liquid crystal systems, two of which are pure materials that exhibit ferroelectric, antiferroelectric, and intermediate phases and one that was developed as a room-temperature SmC* material for electro-optic applications. We report the field-induced temperature changes of these selected materials, measured indirectly using the Maxwell method. The maximum induced temperature change determined, 0.37 K, is currently record-breaking for an FLC and is sufficiently large to make these materials interesting candidates for the development for electrocaloric applications. Using the electrocaloric temperature change normalised as a function of electric field strength, as a function of merit, the performances of FLCs are compared with ferroelectric ceramics and polymers.

Degradation and Breakdown of Polymer/Graphene Composites under Strong Electric Field

In this work, we study the effect of strong electric fields on a polymer/graphene composite and the resulting morphology upon its dielectric breakdown. Our model system was produced by compounding up to 0.25 wt % graphene nanoplatelets (GNP) into poly(ethylene-co-vinyl acetate) (EVA), which is a soft polymer with low melt viscosity. A strong electric field of up to 400 Vrms/mm was applied to the EVA/GNP composite in the melt. The sample’s resistance over the electric field application was simultaneously measured. Despite the low GNP loading, which was below the theoretical percolation threshold, the electric conductivity of the composite during electric field application dramatically increased to >10−6 S/cm over 5 min of electric field application before reaching the current limit of the experimental apparatus. Conductivity growth follows the same scaling relationship of the theoretical model that predicts the rotation and translation time of GNPs in a polymer melt as a function of electric field strength. Since no significant GNP alignment in the composite was observed under transmission electron microscopy (TEM), we hypothesized that the increase in electrical conductivity was due to local electrical treeing of the polymer matrix, which eventually leads to dielectric breakdown of the composite. Electrical treeing is likely initiated by local GNP agglomerates and propagated through conductive channels formed during progressive dielectric breakdown.

Effects of transcranial alternating current stimulation on spiking activity in computational models of single neocortical neurons

Neural oscillations are a key mechanism for information transfer in brain circuits. Rhythmic fluctuations of local field potentials control spike timing through cyclic membrane de- and hyperpolarization. Transcranial alternating current stimulation (tACS) is a non-invasive neuromodulation method which can directly interact with brain oscillatory activity by imposing an oscillating electric field on neurons. Despite its increasing use, the basic mechanisms of tACS are still not fully understood. Here, we investigate in a computational study the effects of tACS on morphologically realistic neurons with ongoing spiking activity. We characterize the membrane polarization as a function of electric field strength and subsequent effects on spiking activity in a set of 25 neurons from different neocortical layers. We find that tACS does not affect the firing rate of investigated neurons for electric field strengths applicable to human studies. However, we find that the applied electric fields entrain the spiking activity of large pyramidal neurons and large basket neurons at < 1 mV/mm field strengths. Our model results are in line with recent experimental studies and can provide a mechanistic framework to understand the effects of oscillating electric fields on single neuron activity. They highlight the importance of neuron morphology and biophysics in responsiveness to electrical stimulation.

Nonlinear ion mobility at high electric field strengths in the perovskites SrTiO3 and CH3NH3PbI3

As the characteristic dimensions of perovskite devices shrink to the nanoscale, operating voltages of a few volts lead to huge field strengths and, consequently, to the possibility of field-enhanced ion mobility. In this paper, the electrochemical mobility of $X$ anions (${u}_{X}$) along $\ensuremath{\langle}100\ensuremath{\rangle}$ in the $AB{X}_{3}$ perovskite structure was investigated as a function of electric field strength $E$ and temperature $T$ by means of classical molecular dynamics simulations. Two different cases were examined: one representative of inorganic perovskites, oxide-ion mobility (${u}_{\text{O}}$) in cubic ${\mathrm{SrTiO}}_{3}$; and the other representative of hybrid inorganic-organic perovskites, iodide-ion mobility (${u}_{\mathrm{I}}$) in cubic ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$. In both cases, isothermal mobilities are, as expected, independent of field at low values ($E&lt;{10}^{0}$ MV ${\mathrm{cm}}^{\ensuremath{-}1}$) but become field dependent at higher values. Data obtained for ${u}_{\text{O}}(E,T)$ can be described quantitatively with an analytical treatment incorporating a modified Haven ratio for a dilute solution. In contrast, ${u}_{\text{I}}(E,T)$ displays complex behavior. At high fields, the degree of field enhancement is underestimated by the analytical treatment, while in the field-independent regime, the data imply that moderate fields decrease ${u}_{\mathrm{I}}$. Our study thus demonstrates that for cubic, inorganic $AB{X}_{3}$ perovskites ${u}_{X}(E,T)$ along $\ensuremath{\langle}100\ensuremath{\rangle}$ can now be predicted quantitatively, but for hybrid perovskites substantially more complex models are required.

Influence of electric field on SHG properties of LN/PMMA nanocomposites

Lithium Niobate (LiNbO3; LN) nanoparticles were dispersed into a polymer matrix, poly(methyl methacrylate) (PMMA) to prepare an organic–inorganic hybrid LN/PMMA nanocomposites. When no electric field was applied during dispersion, the polar LN nanoparticles remain randomly oriented in the PMMA and unpoled nanocomposite is obtained. In this work, poled LN/PMMA nanocomposites were prepared by applying an electric field of varying strength and used to investigate its influence on the second harmonic generation (SHG) properties (λ = 532 nm) using the fundamental laser (λ = 1064 nm). Since the electric field orients the dipoles of the LN nanoparticles inside the PMMA matrix in the direction of the field, a maximum was observed in the SHG signal as a function of electric field strength. The SHG from the differently poled nanocomposite was investigated as a function of LN nanoparticle concentration, fundamental laser energy, and sample thickness. The trend in SHG is explained and the role of induced and spontaneous polarizations in the SHG generation has been specifically highlighted. It has been observed that the effect of electric field on the SHG properties of the nanocomposite was observed only when the factors contributing to the loss of SHG signal are insignificant.

Electro-optic and dielectric properties of polymer networks stabilised short pitch chiral smectic C* liquid crystal

ABSTRACT We present the effect of polymer network on the ferroelectric phase for a polymer stabilised ferroelectric liquid crystal (PSFLC) system. The ferroelectric liquid crystal (FLC) exhibits a very short helical pitch, large tilt angle and relatively high spontaneous polarisation. Electro-optic and dielectric investigations are performed on films with various polymer concentrations. Measurements in the chiral smectic C* (SmC*) phase of the tilt angle and spontaneous polarisation as a function of electric field strength and polymer concentrations were performed. For low electric fields, a deformed helix ferroelectric (DHF) process was observed for pure FLC as well as for the PSFLC films, showing a linear response of the helical structure to electric field. The influence of the polymer network on the FLC properties is also investigated by linear dielectric measurements. Particularly the Goldstone relaxation mechanism. The results reveal a gradual decrease of the dielectric strength with an increase in the network density. However, the relaxation frequency of this mechanism seems to be insensitive to the polymer network density. These behaviours were interpreted by the increase of both the effective elasticity and the rotational viscosity of the SmC* when stabilised by the polymer network.

Understanding Electric and Non-Electric Field Effects on Electrochemical Double Layer Restructuring for the Model Platinum HOR

Recent progresses in hydroxide exchange membrane fuel cells (HEMFCs) have led to renewed interest in the strong pH effect on hydrogen oxidation reaction (HOR) rate on precious metals: two orders of magnitude decrease when pH is changed from 0 to 14.1 Various theories have been proposed to explain this, ranging from adsorbed cation effects, changes in the electric field strength, to pH induced changes to the apparent hydrogen binding energy.2-4 One leading argument is the increase of pH leads to stronger electric field and thus more rigid ordering of water at the electrode/electrolyte interface, resulting in greater resistance to proton/hydroxide transfer through the double layer. This increased energetic barrier due to reorganization results in the decreased activity.5 In this work, we examine this theory by using a combination of traditional electochemical and spectroscopic techniques to highlight the importance of both electric field and non-electric field effects on reaction rates. Further we use this distinction to understand how each factor contributes to water structure re-arrangement on the surface and in the double layer, which we hypothesize to be the pivotal factor in the aforementioned activity decrease from acid to base.The electrochemical double layer is traditionally described by specifically adsorbed species (inner helmholtz plane, IHP), the next layer of hydrated ions (outer Helmholtz plane, OHP) and further layers (diffuse region) protruding and mixing into the bulk electrolyte. It has been shown that the stark tuning rate, which is a function of electric field strength, is dictated by hydrated cation size, and provides a metric to measure the thickness of the electrochemical double layer.6-8 By introducing crown ether to chelate cations, the stark tuning rate, and thus the electric field, can be decreased up to a 0.5:1 ratio of crown ether to cation. Beyond this point, no change in stark tuning rate and electric field were observed. However, further decreases in HOR activity are observed beyond this threshold. This decreasing activity at a constant field strength provides strong evidence for mixed electric and non-electric field effects. We hypothesize that cations and ether molecules impact the electric field strength to a degree, but also interact with surface water species. Spectroscopic and reactivity data demonstrates that both chelating and linear ethers, while having drastically different impacts on the strength of the electric field, result in similar activity decreases. Additionally, both types of ether demonstrate removal of the same types of interfacial water, suggesting that their influence on the surface water structure rather than their effect on the electric field strength determines the HOR activity.(1) Durst, J.; Siebel, A.; Simon, C.; Hasché, F.; Herranz, J.; Gasteiger, H. A. New Insights into the Electrochemical Hydrogen Oxidation and Evolution Reaction Mechanism. Energy Environ. Sci. 2014, 7 (7), 2255–2260. https://doi.org/10.1039/c4ee00440j.(2) Chen, X.; McCrum, I. T.; Schwarz, K. A.; Janik, M. J.; Koper, M. T. M. Co-Adsorption of Cations as the Cause of the Apparent PH Dependence of Hydrogen Adsorption on a Stepped Platinum Single-Crystal Electrode. Angew. Chemie - Int. Ed. 2017, 56 (47), 15025–15029. https://doi.org/10.1002/anie.201709455.(3) Yang, X.; Nash, J.; Oliveira, N. J.; Yan, Y.; Xu, B. Understanding the PH Dependence of Underpotential Deposited Hydrogen on Platinum. Angew. Chemie - Int. Ed. 2019, 58, 17718–17723. https://doi.org/10.1002/ange.201909697.(4) Zheng, J.; Nash, J.; Xu, B.; Yan, Y. Perspective—Towards Establishing Apparent Hydrogen Binding Energy as the Descriptor for Hydrogen Oxidation/Evolution Reactions. J. Electrochem. Soc. 2018, 165 (2), H27–H29. https://doi.org/10.1149/2.0881802jes.(5) Ledezma-Yanez, I.; Wallace, W. D. Z.; Sebastián-Pascual, P.; Climent, V.; Feliu, J. M.; Koper, M. T. M. Interfacial Water Reorganization as a PH-Dependent Descriptor of the Hydrogen Evolution Rate on Platinum Electrodes. Nat. Energy 2017, 2 (4), 1–7. https://doi.org/10.1038/nenergy.2017.31.(6) Ringe, S.; Clark, E. L.; Resasco, J.; Walton, A.; Seger, B.; Bell, A. T.; Chan, K. Understanding Cation Effects in Electrochemical CO 2 Reduction. Energy Environ. Sci. 2019. https://doi.org/10.1039/C9EE01341E.(7) Dunwell, M.; Wang, J.; Yan, Y.; Xu, B. Surface Enhanced Spectroscopic Investigations of Adsorption of Cations on Electrochemical Interfaces †. Phys. Chem. Chem. Phys 2017, 19, 971. https://doi.org/10.1039/c6cp07207k.(8) Waegele, M. M.; Gunathunge, C. M.; Li, J.; Li, X. How Cations Affect the Electric Double Layer and the Rates and Selectivity of Electrocatalytic Processes. J. Chem. Phys. 2019, 151 (16), 160902. https://doi.org/10.1063/1.5124878. Figure 1

Single and ensemble response of colloidal ellipsoids to a nearby ac electrode

Anisotropic colloids can be used as building blocks for fabricating assemblies with complex microstructure and function. External electric fields are one key tool used to assemble such colloidal structures. Herein, we utilized a parallel plate electrode geometry to drive motion of micrometer scale ellipsoidal colloids. The response of pseudo 2D layers of ellipsoids with systematically altered aspect ratios was measured as a function of electric field strength and frequency. We found there to be a weak dependence of ellipsoid ensemble structure on aspect ratio. Namely, regions of aggregation and separation were only slightly dependent on particle aspect ratio. We found that ellipsoids with a smaller aspect ratio tended to align with the electric field, while high aspect ratio ellipsoids did not in response to an electric field of the magnitude and time scale used herein. In addition, we found the kinetics of aggregation of colloids to be very similar regardless of aspect ratio. Complementary experiments utilizing these data demonstrated long-lasting deposition of ellipsoids in energetically unfavorable orientations, which is being used as a model system for the measurement of light scattered from an evanescent wave by an ellipsoid.

Directing Chemistry at Electrodes Using Precisely-Defined Electrochemical Interfaces

Molecular-level understanding of chemistry occurring at electrode-electrolyte interfaces (EEIs) during charge transfer processes as a function of electric field strength and concentration gradient is necessary to enable the rational design of more efficient electrochemical technologies for energy storage. The scientific challenge is to unravel convoluted interfacial interactions (i.e., adsorption, coordination, transport) and control the reaction pathways that lead to formation of desired products over unwanted byproducts. Ultimately the objective is to modulate the evolution of the solid-electrolyte interphase (SEI) in batteries for enhanced performance and durability. Soft landing of mass-selected ions, a versatile approach to surface modification, is ideally suited to preparation of well-defined interfaces with predetermined electrochemically active ions. The “atom-by-atom” precision of ion soft landing enables experiments that unravel the complexity associated with the multitude of interfacial processes occurring simultaneously at electrified interfaces. We present evidence for a substantial advancement in understanding such complex interfacial reactions on Mg battery electrodes employing user-defined layer-by-layer assembly of electrochemically active cations and solvated counter-ions with precisely-selected stoichiometry and concentration. As an example, ion soft landing combined with operando infrared reflection-absorption spectroscopy (IRRAS) and in-situ x-ray photoelectron spectroscopy (XPS) was used to characterize the decomposition of counter electrolyte anions and solvent molecules on Mg electrodes. Furthermore, we explored using an aliovalent doped metal (e.g., Al) on the Mg surface to control the decomposition and stabilize the SEI layer formation as a function of both concentration and potential. Our in-situ multimodal analysis enabled the capture of spectroscopic signatures from key chemical transformations of electrolyte anions and solvent molecules on reactive metal surfaces. These experimental results were correlated with the evolution of the SEI layer as predicted by theory to provide molecular-level insight into the reaction mechanism. In summary, our unique approach allowed us to acquire more delineated understanding of electrochemical transformations across length scales in operating EEIs and aids in the rational design of improved sustainable electrochemical energy technologies.

Electric Volume Resistivity for Biopolyimide Using 4,4'-Diamino-α-truxillic acid and 1,2,3,4-Cyclobutanetetracarboxylic dianhydride.

Biopolyimides poly(ATA-CBDA), made from of 4,4′-diamino-α-truxillic acid dimethyl ester (ATA) and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), is synthesized and measured its electric volume resistivity at various experimental conditions. The effects of film size, thickness, drying time, and the electric field strength on electric resistivity are investigated and compared with polyimide (Kapton). The electric resistivity for all polyimide and biopolyimide are distributed in the range of 1015–1016 Ωcm, which shows that biopolyimide has high electrical insulation as well as polyimide. The electric resistivity strongly depends on film thickness, which suggests that electric resistivity is a function of electric field strength. The critical electric field for polyimide and biopolyimide films are determined to be 5.8 × 107 V/m and 3.2 × 107 V/m, respectively. Humidity was found to strongly affect the electric resistivity; ~1016 Ωcm at 34% RH and ~1013 Ωcm at 60% RH for both polyimide and biopolyimide films.

Effect of electric field strength on electro-dewatering efficiency for river sediments by horizontal electric field

A series of electro-dewatering experiments were conducted to explore the effect of sediment cake thickness (1–5 cm) and electric field strength (2–50 V cm−1). The final dry solids content, energy consumption and dewatering productivity were modeled and the validity of the model was tested. It was demonstrated that the electric field strength determines final dry solids content and the power utilization is an exponential function of electric field strength. It was also found that a relatively low electric field strength (<10 V cm−1) significantly decreased energy consumption while maintaining an acceptable dry solids content. These findings are beneficial to practical applications of electro-dewatering.

Covalent character and electric field dependence of H2-AgX (X = F - I).

Mechanisms of Ag-X and Ag…H2 interactions and stabilities of T-shaped H2-AgX (X = F - I) series were investigated at the CCSD(T) level. The "no-density" bond with smaller positive Laplacian and ELF values in interaction regions, as well as considerable delocalization index values, suggest weak covalent "charge-shift" character for the Ag…H2 interaction. Structure and stability dependence on the electric field were investigated at the MP2 level. Relative total energy curves show obvious parabolic character, and the plots can be fitted by quadratic polynomials as functions of electric field strength.

Effective ionization coefficient of C5 perfluorinated ketone and its mixtures with air

C5 perfluorinated ketone (C5 PFK with UIPAC chemical name 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)-2-butanone and sold by 3M as Novec™ 5110) has a high dielectric strength and a low global warming potential, which makes it interesting as an insulating gas in medium and high-voltage applications. The study was carried out to determine the effective Townsend ionization coefficient αeff as a function of electric field strength and gas density for C5 PFK and for its mixtures with air. The non-self-sustained Townsend discharge between parallel plate electrodes was initiated by illuminating the cathode by UV radiation. The discharge current, I, was measured as a function of inter-electrode distance, d, at different gas densities, N, and electric field strengths, E. The effective ionization coefficient αeff was determined from the semi-logarithmic plots of I/I0 against d. For each tested gas mixture, the density normalized effective ionization coefficient αeff/N was found to be a unique function of reduced electric field strength E/N. The measurements were carried out in the absolute pressure range of 0.05–1.3 bar and E/N range of 150–1200 Td. The increasing fraction of C5 PFK in air resulted in the decrease of effective ionization coefficient. The limiting electric field strength (E/N)lim where the effective ionization coefficient αeff became zero was 770 Td (190 kV cm−1 at 1 bar) for pure C5 PFK and decreased to 225 Td (78 kV cm−1 at 1.4 bar) for 7.6% C5 PFK/air mixture. The latter value of (E/N)lim is still more than two times higher than the (E/N)lim value of synthetic air and about two-thirds of the value corresponding to pure SF6. The investigated gas mixtures have the potential to become an alternative to SF6 in numerous high- and medium-voltage applications.

Comparative study of the electrorheological effect in suspensions of needle-like and isotropic cerium dioxide nanoparticles

A novel approach to the analysis of the electrorheological effect is proposed, based on the expansion of dimensionless relative shear stress as function of electric field strength in the power series $$ {\tau}_{\mathrm{rel}}=\frac{\tau_E}{\tau }=1+\frac{\alpha }{\tau }E+\frac{\beta }{\tau }{E}^n $$ . The application of this approach to investigation of the electrorheological effect in suspensions of isotropic and needle-like CeO2 nanoparticles in polydimethylsiloxane has revealed that the polynomial coefficients can be judged as a measure of the efficiency of transformation of electrical energy into mechanical energy. The values of α and β coefficients depend on the shape and concentration of filler particles, as well as on the shear rate. The value and the sign of these coefficients determine both the magnitude of the electrorheological effect and the type of dependence of the shear stress (linear or power law) on the strength of the electric field. It has been shown that the values of α and β coefficients for the electrorheological fluids with needle-like particles are greater than for fluids with isotropic particles (at the same concentration of suspensions), which is associated with the different polarization of particles in the applied electric field.

Effect of Electric Field on Energy Spectrum and Intersubband Absorption Coefficient of Electron in Spherical Multilayered Quantum dot CdSe/ZnS/CdSe

In this paper, the energy spectrum of electron and complete set of exact wave functions are obtained in the framework of effective mass approximation and rectangular potential barriers model for the CdSe/ZnS/CdSe nanostructure. Using the matrix method, the numeric calculations are performed for the electron energy spectrum as a function of electric field strength in multilayered quantum dot. It is shown that the electric field effects on the core electron in the ground state and causes its tunneling into the outer potential well. Thus, the overlap of wave functions varies essentially, influencing the dipole momentum of quantum transitions and light absorption coefficient.

Tracking ferroelectric domain growth using laser scattering tomography

The movement and growth of macroscopic ferroelectric domains in a crystal under an electric field (poling voltage) have been studied using laser scattering tomography, a technique heretofore used mainly for studying microscopic defects in crystals. This technique involves scanning successive planes in a crystal with a laser beam and collecting the scattered light in a computer. The data collected can then be visualized as two- or three-dimensional static images or as a video to study structural changes as a function of time. An important feature of this method is that these images can be viewed along any axis in the crystal. Using this technique, we were able to generate images of domain wall nucleation and growth as a function of electric field strength and time. It also allowed for the observation of domain wall movement along any crystallographic direction including down the poling axis which is covered with opaque metallic electrodes. Details of the technique and its use during the poling of a strontium barium niobate crystal are discussed.

Surface isoelectric focusing (sIEF) with carrier ampholyte pH gradient

Isoelectric focusing (IEF) is a powerful tool for amphoteric protein separations because of high sensitivity, bio-compatibility, and reduced complexity compared to chromatography or mechanical separation techniques. IEF miniaturization is attractive because it enables rapid analysis, easier adaptation to point of care applications, and smaller sample demands. However, existing small-scale IEF tools have not yet been able to analyze single protein spots from array libraries, which are ubiquitous in many pharmaceutical discovery and screening protocols. Thus, we introduce an in situ, novel, miniaturized protein analysis approach that we have termed surface isoelectric focusing (sIEF). Low volume printed sIEF gels can be run at length scales of ∼300μm, utilize ∼0.9ng of protein with voltages below 10V. Further, the sIEF device platform is so simple that it can be integrated with protein library arrays to reduce cost; devices demonstrate reusability above 50 uses. An acrylamide monomer solution containing broad-range carrier ampholytes was microprinted with a Nano eNablerTM between micropatterned gold electrodes spaced 300μm apart on a glass slide. The acrylamide gel was polymerized in situ followed by protein loading via printed diffusional exchange. A pH gradient formed via carrier ampholyte stacking when electrodes were energized; the gradient was verified using ratiometric pH-sensitive FITC/TRITC dyes. Green fluorescent protein (GFP) and R-phycoerythrin (R-PE) were utilized both as pI markers and to test sIEF performance as a function of electric field strength and ampholyte concentration. Factors hampering sIEF included cathodic drift and pH gradient compression, but were reduced by co-printing non-ionic Synperonic® F-108 surfactant to reduce protein-gel interactions. sIEF gels achieved protein separations in <10min yielding bands < 50μm wide with peak capacities of ∼8 and minimum pI differences from 0.12 to 0.14. This new sIEF technique demonstrated comparable focusing at ∼100 times smaller dimensions than any previous IEF. Further, sample volumes required were reduced four orders of magnitude from 20μL for slab gel IEF to 0.002μL for sIEF. In summary, sIEF advantages include smaller volumes, reduced power consumption, and microchip surface accessibility to focused bands along with equivalent separation resolutions to prior IEF tools. These attributes position this new technology for rapid, in situ protein library analysis in clinical and pharmaceutical settings.