The electrical properties of leg skin in normal individuals and in patients with ischemia

Measurements of skin electrical admittance were performed on the leg in healthy controls and patients with ischemia. The experiments were carried out using sinusoidal wave voltage at seven frequencies from 100 Hz to 100 kHz applied using two electrodes. The character of the frequency dependencies of admittance for both groups arises from stratum corneum--in the frequencies up to 10 kHz, and the underlying tissue of skin, above this frequency. Legs change their passive electrical properties due to ischemia. The measured data are interpreted as cell membranes become more permeable and thus an efflux of intracellular electrolyte.     

Micromachined impedance spectroscopy flow cytometer for cell analysis and particle sizing

A new cytological tool, based on the microCoulter particle counter (microCPC) principle, aimed at diagnostic applications for cell counting and separation in haematology, oncology or toxicology is described. The device measures the spectral impedance of individual cells or particles and allows screening rates over 100 samples s(-1) on a single-cell basis. This analyzer is intended to drive a sorting actuator producing a subsequent cell separation. Size reduction and integration of functions are essential in achieving precise measurements and high throughput. 3D finite element simulations are presented to compare various electrode geometries and their influence on cell parameters estimation. The device is based on a glass-polyimide microfluidic chip with integrated channels and electrodes microfabricated at the length scale of the particles to be investigated (1-20 microm). A laminar liquid flow carries the suspended particles through the measurement area. Each particle's impedance signal is recorded by a differential pair of microelectrodes using the cell surrounding media as a reference. The micromachined chip and processing electronic circuit allow simultaneous impedance measurements at multiple frequencies, ranging from 100 kHz to 15 MHz. In this paper, we describe the microfabrication and characterisation of an on-chip flow-cytometer as the first building block of a complete cell-sorting device. We then discuss the signal conditioning technique and finally impedance measurements of cells and particles of different sizes and types to demonstrate the differentiation of subpopulations in a mixed sample.     

A four-electrode microconstant direct current resistance detector for ion chromatography applying ion-exchange membrane and porous electrode

A four-electrode microconstant direct current resistance detector for ion chromatography not sensitive to the effects of electrode polarization, capacitance, and electrolysis by-products is proposed. A constant current of microampere magnitude is applied across the current electrodes of the four-electrode device, and the voltage responses between the detection probes are directly picked up by a high input impedance instrumentation amplifier. The ion-exchange membranes, which separate the detection chamber from the electrolysis chambers, enable the measurement of solution resistance free of the interference of electrolysis by-products. Two resin beds in the detection chamber serve as ion conductors while reduce the dead volume of the detector. Recycled detection effluent supplies water for the electrolysis reactions at the current electrodes to sustain constant current in solution. The porous detection probes provide microchannel for the flowing solution while indicating signals. Owing to the constant current excitation, the electronics setup becomes simple. The cell configuration, operating principle, electronics, and error analysis of this detection mode are discussed along with their use for suppressed anion chromatography. Experimental data show that this four-electrode direct current detection mode is comparable to conventional two-electrode alternating current method.     

Development of a new contactless dielectrophoresis system for active particle manipulation using movable liquid electrodes

This study presents a new DEP manipulation technique using a movable liquid electrode, which allows manipulation of particles by actively controlling the locations of electrodes and applying on–off electric input signals. This DEP system consists of mercury as a movable liquid electrode, indium tin oxide (ITO)‐coated glass, SU‐8‐based microchannels for electrode passages, and a PDMS medium chamber. A simple squeezing method was introduced to build a thin PDMS layer at the bottom of the medium chamber to create a contactless DEP system. To determine the operating conditions, the DEP force and the friction force were analytically compared for a single cell. In addition, an appropriate frequency range for effective DEP manipulation was chosen based on an estimation of the Clausius–Mossotti factor and the effective complex permittivity of the yeast cell using the concentric shell model. With this system, we demonstrated the active manipulation of yeast cells, and measured the collection efficiency and the dielectrophoretic velocity of cells for different AC electric field strengths and applied frequencies. The experimental results showed that the maximum collection efficiency reached was approximately 90%, and the dielectrophoretic velocity increased with increasing frequency and attained the maximum value of 10.85 ± 0.95 μm/s at 100 kHz, above which it decreased.     

SEM and ECIS Investigation of Cells Cultured on Nanopillar Modified Interdigitated Impedance Electrodes for Analysis of Cell Growth and Cytotoxicity of Potential Anticancer Drugs

Cell‐based biosensors treat living cells as sensing elements and are able to detect the functional information of biologically active analytes. Monitoring cytotoxicity with high sensitivity, rapidity and at low cost is of great interest in the fields of clinical diagnostics, environmental monitoring, food safety and security. This research investigates the behaviour of different cell types on nanostructured architectures. The development of cell‐based assays using bioimpedance devices has the potential of screening anti‐cancer drugs; these have a potential impact for developing new techniques and tools for the analysis of cells in the bio‐pharma industry. Gold impedance electrodes have been successfully fabricated for impedance measurement on cells cultured on the electrode surface which was modified with gold nanopillars with a height of 60 nm and 150 nm diameter in a highly ordered layout thanks to the e‐beam lithography technique. This article investigates the effects on the sensitivity achieved with the ECIS (Electric Cell‐substrate Impedance Spectroscopy) measurements while monitoring the cytotoxicity of two different drugs (Antrodia Camphorata extract and Nicotine) on different cell lines (HeLa, A549 and BALBc 3T3) cultured on the nanostructured devices. The change of morphology of cells growing on the nanostructured electrodes was also investigated through SEM imaging.     

Hybridization-induced interfacial changes detected by non-Faradaic impedimetric measurements compared to Faradaic approach

A biosensor for direct label-free DNA detection based on a polythiophene matrix is investigated by electrochemical impedance spectroscopy (EIS). Impedimetric experiments are performed with and without redox probe in solution. The non-Faradaic impedance measurements reveal two relaxation processes located at 50 Hz and 5 kHz, respectively. The first relaxation process, located at low frequencies, allows to detect biorecognition events by measuring the phase angle decrease, in accordance with a hindrance of the polaronic conduction. The second relaxation process, located at 5 kHz and originating from DNA modification, seems to increase with the length of the target sequence. These results suggest that this loaded support provides a platform for impedimetric detection of hybridization at high frequencies, leading to less time-consuming detection procedure. For a better understanding, results obtained in non-Faradaic mode are compared with Faradaic approach.     

Size and medium conductivity dependence on dielectrophoretic behaviors of gas core poly‐l‐lysine shell nanoparticles

Dynamic (dis)assembly of biocompatible nanoparticles into 3D, packed structures would benefit drug delivery, films, and diagnostics. Dielectrophoretic (DEP) microdevices can rapidly assemble and manipulate polarizable particles within nonuniform electric fields. DEP has primarily discerned micrometer particles since nanoparticles experience smaller forces. This work examines conductivity and size DEP dependencies of previously unexplored spherical core‐shell nanoparticle (CSnp) into 3D particle assemblies. Poly‐l ‐lysine shell material was custom synthesized around a gas core to form CSnps. DEP frequencies from 1 kHz to 80 MHz at fixed 5 volts peak‐to‐peak and medium conductivities of 10^?5 and 10^?3 S/m were tested. DEP responses of ～220 and ～400 nm poly‐l ‐lysine CSnps were quantified via video intensity densitometry at the microdevice's quadrapole electrode center for negative DEP (nDEP) and adjacent to electrodes for positive DEP. Intensity densitometry was then translated into a relative DEP response curve. An unusual nDEP peak occurred at ～57 MHz with 25–80 times greater apparent nDEP force. All electrical circuit components were then impedance matched, which changed the observed response to weak positive DEP at low frequencies and consistently weak nDEP from ～100 kHz to 80 MHz. This impedance‐matched behavior agrees with conventional Clausius–Mossotti DEP signatures taking into account the gas core's contributions to the polarization mechanisms. This work describes a potential pitfall when conducting DEP at higher frequencies in microdevices and concurrently demonstrates nDEP behavior for a chemically and structurally distinct particle system. This work provides insight into organic shell material properties in nanostructures and strategies to facilitate dynamic nanoparticle assemblies.     

A contactless conductivity detector for capillary electrophoresis: effects of the detection cell geometry on the detector performance

The effect of the gap between the electrodes and of their width on the behavior of a capacitively wired contactless conductivity detector was studied. The results obtained have indicated that the detector response can be qualitatively described by a model based on the concept of the effective electrode width which is a complex parameter determined by the gap between the electrodes, the frequency of the input signal and the conductivity of the test solution. The detector sensitivity and the effect on the separation efficiency depend on the difference between the effective and geometric electrode widths. Higher detection sensitivities have been attained for detectors with wide electrodes operating at lower frequencies, however, better separation efficiencies have been achieved using detectors with narrow electrodes and higher operational frequencies. The noise increases with decreasing gap between the electrodes and increasing frequency, especially with detectors employing narrow electrodes.     

Analytical and Numerical Modeling Methods for Electrochemical Impedance Analysis of Single Cells on Coplanar Electrodes

Impedance measurements provide basic electrical properties and are used to analyze the characteristics of electrochemical materials for biomedical applications. The extracellular fluid (ECF) in microfluidic devices greatly affects the accuracy of impedance measurements of cells. When a single cell is placed in large amounts of ECF, the electric current mostly passes through the ECF, not the cell. Hence, this work presents a modeling method that is demonstrated in numerical and analytical solutions for eliminating the effect of ECF in coplanar impedance sensors. The proposed modeling method uses fundamental formulas of circuits that include the electrical parameters of the ECF, cytoplasm, and cell membrane. Equivalent circuit models for the coplanar impedance sensor are established to simulate the impedance as well as the measured ones for excitation frequencies in the range of 11–101 kHz. According to the calculation result using the proposed modeling method, the cytoplasm resistance, membrane capacitance, medium resistance, and medium capacitance of HeLa (human cervix adenocarcinoma) cell are 13.5 kΩ, 122.6 pF, 27.9 kΩ, and 337.7 pF, respectively. Moreover, the electric current distribution in the coplanar impedance sensor is investigated using finite element method (FEM) simulation software. The variation in the impedance during measurements with the simultaneous application of an alternating‐current (AC) voltage amplitude of 0.4 V_pp in the fluid volume range of 9–144 µL is also studied.     

De Novo 3D Structure Determination from Sub‐milligram Protein Samples by Solid‐State 100 kHz MAS NMR Spectroscopy

Solid‐state NMR spectroscopy is an emerging tool for structural studies of crystalline, membrane‐associated, sedimented, and fibrillar proteins. A major limitation for many studies is still the large amount of sample needed for the experiments, typically several isotopically labeled samples of 10–20 mg each. Here we show that a new NMR probe, pushing magic‐angle sample rotation to frequencies around 100 kHz, makes it possible to narrow the proton resonance lines sufficiently to provide the necessary sensitivity and spectral resolution for efficient and sensitive proton detection. Using restraints from such spectra, a well‐defined de novo structure of the model protein ubiquitin was obtained from two samples of roughly 500 μg protein each. This proof of principle opens new avenues for structural studies of proteins available in microgram, or tens of nanomoles, quantities that are, for example, typically achieved for eukaryotic membrane proteins by in‐cell or cell‐free expression.     

The promise of electrochemical impedance spectroscopy as novel technology for the management of patients with diabetes mellitus

Self-monitoring of blood glucose is the standard of care in management of hyperglycemia among patients with diabetes mellitus. To increase the sensitivity and specificity of current devices, a novel method of detecting glucose using electrochemical impedance spectroscopy (EIS) technology is explored. The enzyme glucose oxidase (GOx) was fixed to gold electrodes and a sine wave of sweeping frequencies was induced using a wide range of concentrations of glucose. Each frequency in the impedance sweep was analyzed for the highest response and R-squared value. The frequency with both factors optimized is specific for the glucose-GOx binding interaction and was determined to be 1.17 kHz in purified solutions in both higher and lower ranges of glucose. The correlation between the impedance response and concentration at the low range of detection (0-100 mg dL(-1) of glucose) was determined to be 3.53 ohm/ln (mg dL(-1)) with an R-squared value of 0.90 with a 39 mg dL(-1) lower limit of detection. The same frequency of 1.17 kHz was verified in whole blood under the same glucose range. The above data confirm that EIS offers a new method of glucose detection as an alternative to current technology in use by patients. Additionally, the unique frequency response of individual markers allows for modulation of signals so that several other markers important in the management of diabetes could be measured with a single sensor.     

A Solar Cell That Is Triggered by Sun and Rain

All‐weather solar cells are promising in solving the energy crisis. A flexible solar cell is presented that is triggered by combining an electron‐enriched graphene electrode with a dye‐sensitized solar cell. The new solar cell can be excited by incident light on sunny days and raindrops on rainy days, yielding an optimal solar‐to‐electric conversion efficiency of 6.53 % under AM 1.5 irradiation and current over microamps as well as a voltage of hundreds of microvolts by simulated raindrops. The formation of π‐electron|cation electrical double‐layer pseudocapacitors at graphene/raindrop interface is contributable to current and voltage outputs at switchable charging–discharging process. The new concept can guide the design of advanced all‐weather solar cells.     

Li/SOCl_2、BCX电池放电电压滞后研究

应用交流阻抗法研究Li/SOCl2、BCX电池放电过程碳、锂电极阻抗变化并测试外加电压和并联超电容对电池放电初期电压的影响.测试表明,锂电极阻抗在放电初期迅速减小了80%~90%,直到放电末期,阻抗几乎不变;碳电极阻抗至放电末期才迅速增大;BCX电池有较高开路电压可改善放电电压滞后;电池并联超级电容器可抑制放电电压滞后.     

Dielectrophoretic field‐flow fractionation of electroporated cells

We describe the development and testing of a setup that allows for DEP field‐flow fractionation (DEP‐FFF) of irreversibly electroporated, reversibly electroporated, and nonelectroporated cells based on their different polarizabilities. We first optimized the channel and electrode dimensions, flow rate, and electric field parameters for efficient DEP‐FFF separation of moderately heat‐treated CHO cells (50°C for 15 min) from untreated ones, with the former used as a uniform and stable model of electroporated cells. We then used CHO cells exposed to electric field pulses with amplitudes from 1200 to 2800 V/cm, yielding six groups containing various fractions of nonporated, reversibly porated, and irreversibly porated cells, testing their fractionation in the chamber. DEP‐FFF at 65 kHz resulted in distinctive flow rates for nonporated and each of the porated cell groups. At lower frequencies, the efficiency of fractionation deteriorated, while at higher frequencies the separation of individual elution profiles was further improved, but at the cost of cell flow rate slowdown in all the cell groups, implying undesired transition from negative into positive DEP, where the cells are pulled toward the electrodes. Our results demonstrate that fractionation of irreversibly electroporated, reversibly electroporated, and nonelectroporated cells is feasible at a properly selected frequency.     

AlN on nanocrystalline diamond piezoelectric cantilevers for sensors/actuators

Micro-cantilevers can be used as both sensors and actuators. In this work, the design, fabrication and characterization of piezoelectrically driven nano-crystalline diamond (NCD) cantilevers are reported Diamond films were grown on silicon (100) substrates by microwave plasma enhanced chemical vapor deposition (MW-PECVD). Cantilevers are coated by DC pulsed piezoelectric with AlN films that is sandwiched between two metallic electrodes. The thicknesses of AlN and diamond layers are 1μm and 700nm, respectively. The influence on the electromechanical response of cantilevers length was studied. The motion of the electrically driven cantilevers is performed by measuring the evolution of the electrical impedance at the resonant frequencies that varies between 10 kHz and 130 kHz for the resonant mode.     

Automated Conductometry Measurements of Simple Electrolytes and Micellar Solutions Using a Voltage Divider Technique

A new automated technique was developed for online monitoring of the conductance of a conductive type of cell. Shining metal electrodes were used for the conductometry measurements and the frequency of the input signal was swept from a few hertz to 1 MHz. A theoretical model was developed based on the voltage dividing technique. The model was in good agreement with the experimental results. Conductances of simple electrolytes such as HCl and micellar solutions were compared. Solutions of HCl with concentrations as low as 45 μmol⋅L⁻¹ were investigated. Critical micellar concentrations of two types of micelles, SDS and CPC, were also measured. It was shown that this voltage divider circuit can be used for automated online conductometric titrations.     

Two-dimensional impedance imaging of cell migration and epithelial stratification

We present a miniaturized impedance imaging system, developed for 2D imaging of cell and tissue culture. The system is based on 16 microelectrodes (5 microm x 4 mm). An equivalent circuit for four-point (tetrapolar) impedance spectra was developed and validated. The system uses an Agilent 4294A impedance analyser combined with a front-end amplifier for the impedance measurements. Human epithelial stem cells (YF 29) were grown on the device surface. Cell migration speeds of 300 nm min(-1) following a "scratch" wound closure assay could be established. Using a commercial software developed for geophysical prospecting, we could generate impedance tomography images at 10 kHz revealing cell migration, increase of epithelial thickness and changes in tissue resistivity over a time course of several days.     

Impedance Study of GaN and InGaN Semiconductor Anion Selective Electrodes

The response of potentiometric anion selective electrodes employing undoped GaN or In_0.2Ga_0.8N films as sensing element to detect various anions was investigated in solutions of KF, KNO₃, KCl, HOC₆H₄COONa, KSCN, CH₃COOK, KClO₄ and KBr salts. The calibration plots for the GaN and In_0.2Ga_0.8N semiconductor electrodes contained linear regions extending over four decades of activity change in most solutions. The structure of the GaN and In_0.2Ga_0.8N semiconductor electrode/ electrolyte interface was studied through electrochemical impedance spectroscopy. Analogous equivalent circuits modeling the GaN or In_0.2Ga_0.8N electrode/electrolyte interface were proposed and their parameters were calculated. The space charge layer of the GaN and In_0.2Ga_0.8N semiconductors dominated the impedance of the electrochemical system at high frequencies (>10 kHz), whereas at low frequencies (<10 kHz), the impedance was controlled by the diffusion of electroactive species across the layer of adsorbed ions at the surface of the electrode. Results imply a strong dependence of the electrodes performance on the adsorption capacity of tested anions.     

A Contactless Impedance Probe for Simple and Rapid Determination of the Ratio of Liquids with Different Permittivities in Binary Mixtures

Simple contactless cells with planar or tubular electrodes have been designed for measurement of the permittivity of solutions. The cells, connected to an integrated circuit of astable multivibrator, respond primarily to the capacitance component of the cell impedance, the multivibrator frequency depends in a defined manner on the solution permittivity and is readily used as the analytical signal in determinations of the ratios of components in binary liquid mixtures; water solution of methanol, ethanol and dioxane have been tested. The response of the cell with planar electrodes satisfies well the simple theoretical model and both the cells provide results with a sufficient sensitivity, a low LOD value (units of %vol) and a good precision (around 1%rel). The cell simplicity, small dimensions, long‐term stability and the possibility of powering them from a battery make them suitable for hand‐held meters. As an example of application in practice, the content of ethanol was determined in the car fuel petrol.     

Electrical impedance spectroscopy for detection of bacterial cells in suspensions using interdigitated microelectrodes

In this study, we present a new, simple and rapid impedance method to detect bacterial cells by making use of the impedance properties of bacterial cell suspensions using interdigitated microelectrodes. It was found that bacterial cell suspensions in deionized (DI) water with different cell concentrations could generate different electrical impedance spectral responses, whereas cell suspensions in phosphate buffered saline (PBS) solution could not produce any significant differences in impedance spectra in response to different cell concentrations. In DI water suspensions, impedance at 1 kHz decreased with the increasing cell concentrations in the suspensions. The impedance of cell suspensions in DI water was discussed and found that it was resulted from the cell wall charges and the release of ions or other osmolytes from the cells. A linear relationship between the impedance and the logarithmic value of the cell concentration was found in the cell concentration range from 10⁶ to 10¹⁰ cfu/ml, which can be expressed by a regression equation of Z (kΩ) = −2.06 log C (cells/20 μl) + 5.23 with R² = 0.98. The detection limit was calculated to be 3.45 × 10⁶ cfu/ml, which is comparable with many label-free immunosensors for detection of pathogenic bacteria reported in the literature. To achieve the selectivity of this method, we also demonstrated the feasibility of integrating magnetic separation to this impedance method. This study has demonstrated that bacterial cell concentration can be inferred by measuring the impedance of cell suspensions in DI water. This new detection mechanism could be an alternative to current impedance methods that have been reported for the detection of bacterial cells, e.g. impedance microbiology and electrical/electrochemical impedance biosensors.