Impedance modelling of two-phase solid-state ionic conductors. Part I—theoretical model and computer simulations

An equivalent circuit model is introduced to account for the impedance properties of solid state ionic conductors, composed of two distinct phases. The model is developed on the basis of physical arguments, regarding the micrometer-scale structure of the two-phase material system and the comparison of different possible equivalent circuit representations. The final equivalent circuit reduces to two simpler circuits, suitable for fitting experimental impedance spectra. Computer simulations are provided to demonstrate the non-Arrhenius behaviour, which is observed in the temperature dependence of the ohmic elements of the equivalent circuits used for data analysis. This complex dual-slope behaviour of the Arrhenius plot is in agreement with the predictions of the model. Finally, with the aid of mathematical calculations and illustrated by computer simulations, a modified Arrhenius plot evaluation procedure was developed to derive correctly the electrical properties of the individual constituent phases from impedance measurements.     

Impedance modelling of two-phase solid-state ionic conductors. Part II—application to high-lithium-content <Emphasis Type="Italic">x</Emphasis>Li<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript> fast-ion conducting glasses

The equivalent circuit model of two-phase ionic conductors, introduced in Part I of this work, was applied to a set of xLi₂O–B₂O₃ fast-ion conducting glasses, with x ranging from 3.0 to 4.5. The shape of Arrhenius plots, constructed by equivalent circuit fitting of impedance spectra measured at various temperatures, turned out to be in agreement with the predictions of the model. The analysis procedure, which was developed by mathematical investigation in accordance with the implications of the model, was employed to determine the activation energies of the two present phases and the total DC ionic resistivity of the examined glasses.     

Impedance spectroscopy of lithium-tin film electrodes

A method of electrochemical impedance spectroscopy was used to study the reversible lithium intercalation from nonaqueous electrolyte into tin films with the thickness of 0.1–1 μm. The impedance spectra of lithium-tin (Li _x Sn) electrodes have a complicated shape depending on the electrode state and prehistory; they reflect the occurrence of several consecutive and parallel processes, including the lithium migration, diffusion, and accumulation. The formation of a solid-electrolyte layer on the surface at Li intercalation into Sn is observed. Equivalent circuits are proposed that adequately model the experimental data on the Li _x Sn electrodes both freshly prepared and after prolonged cycling. Problems associated with the choice of equivalent circuits and determination of their parameters, the accuracy of the diffusion coefficient determination, the trends in the parameters’ variation with electrode potential (composition) are discussed.     

Impedance spectroscopy investigation of the water-in-oil microemulsions formation

In this work it was investigated the microemulsion formation using impedance spectroscopy analysis. The results indicated that the microemulsion formation is clearly observed on the impedance complex plane. The phase transition related with microemulsion formation is characterized by a time relaxation distribution. In the condition of the microemulsion formation, the impedance spectra are characterized by a single relaxation time.     

Electrochemical Impedance of Ethanol Oxidation in Alkaline Media

Nickel modified NiOOH electrodes were used for the electrocatalytic oxidation of ethanol in alkaline solutions. The electro-oxidation of ethanol in a 1 mol/L NaOH solution at different concentrations of ethanol was studied by ac impedance spectroscopy. Electrooxidation of ethanol on Ni shows negative resistance on impedance plots. The impedance shows different patterns at different applied anodic potential. The influence of the electrode potential on impedance was studied and a quantitative explanation for the impedance of ethanol oxidation was given by means of a proposed mathematical model. At potentials higher than 0.52 V(vs. Ag/AgCl), a pseudoinductive behavior was observed, but at those higher than 0.57 V, impedance patterns were reversed to the second and third quadrants. The conditions required for the reversing of impedance pattern were delineated with the impedance model.     

Conductivity studies of some diphosphates with the general formula AI2BIIP2O7 by impedance spectroscopy

The conductivity mechanism of three crystalline diphosphates of (A^I₂B^IIP₂O₇) type, Na₂CaP₂O₇, Na₂CuP₂O₇ and K₂MnP₂O₇ has been investigated using combined complex impedance and modulus formalisms. Their conductivity measurements showed that Na₂CaP₂O₇ and Na₂CuP₂O₇ can be considered as pure ionic conductors, while K₂MnP₂O₇ is a mixed ionic-electronic conductor with a relatively electronic nature. In the case of K₂MnP₂O₇, the electron transport, originated from the electronic hopping, is due to the presence of various oxidation states of the manganese ion. The conductivity measurements of the diphosphate compounds have been carried out using the frequency range between 10^?1 and 10⁶ Hz over a temperature interval from 300 to 700 K. The equivalent circuit, which provides the most realistic model of the electrical properties of each compound under investigation, was studied using the least squares immittance fitting program (LEVEM). A correlation between electrical and structural properties of the diphosphates has been conducted.     

基于叉指阵列微电极的阻抗免疫传感器研究进展

叉指阵列微电极(Interdigitated array microelectrodes,IDAM)具有检出限低、灵敏度高和信噪比好等优点,近年来在分析化学领域引起了极大的关注.阻抗免疫传感器将IDAM与免疫测定技术相结合,通过抗原抗体的特异性反应引起IDAM之间介质的阻抗变化实现对目标物的检测.本文分析了 IDAM的...     

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.     

Label-Free Impedance Biosensors: Opportunities and Challenges

Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research.     

Impedance spectroscopy of lithium-carbon electrodes

The methods of coulometric titration and electrode impedance spectroscopy are used in studying the behavior of carbon film electrodes free of binding and conducting additives in the course of reversible lithium intercalation from nonaqueous electrolytes. The electrodes with the high and low degrees of graphitization are studied. The measurements are performed in the frequency range from 10⁵ to 10^?2 Hz with the lithium concentration in intercalate varied from 0.025 mol/cm³ (corresponds to LiC₆) to a state free of lithium. The factors responsible for the hysteresis in charge-discharge curves, the versions of equivalent circuits (EC) suitable for modeling the impedance spectra of Li _x C₆ electrodes, the dependence of EC parameters and the lithium diffusion coefficient on the concentration are discussed. It is shown that all experimental impedance spectra can be adequately modeled by a common general EC. The concentration dependences are consistent with the earlier data of pulse methods. The diffusion coefficient varies approximately from 10^?12 to 10^?13 cm²/s.     

Dielectric spectroscopy of red blood cells in sickle cell disease

Hypoxia-induced polymerization of sickle hemoglobin and the related ion diffusion across cell membrane can lead to changes in cell dielectric properties, which can potentially serve as label-free, diagnostic biomarkers for sickle cell disease. This article presents a microfluidic-based approach with on-chip gas control for the impedance spectroscopy of suspended cells within the frequency range of 40 Hz to 110 MHz. A comprehensive bioimpedance of sickle cells under both normoxia and hypoxia is achieved rapidly (within ∼7 min) and is appropriated by small sample volumes (∼2.5 μL). Analysis of the sensing modeling is performed to obtain optimum conditions for dielectric spectroscopy of sickle cell suspensions and for extraction of single cell properties from the measured impedance spectra. The results of sickle cells show that upon hypoxia treatment, cell interior permittivity and conductivity increase, while cell membrane capacitance decreases. Moreover, the relative changes in cell dielectric parameters are found to be dependent on the sickle and fetal hemoglobin levels. In contrast, the changes in normal red blood cells between the hypoxia and normoxia states are unnoticeable. The results of sickle cells may serve as a reference to design dielectrophoresis-based cell sorting and electrodeformation testing devices that require cell dielectric characteristics as input parameters. The demonstrated method for dielectric characterization of single cells from the impedance spectroscopy of cell suspensions can be potentially applied to other cell types and under varied gas conditions.     

Biomimetic Electroreduction of O2 by Hemoglobin in a Surfactant Film: Preliminary Electrochemical Impedance Spectroscopy Insight

We report in this study on the direct electron transfer for hemoglobin (Hb) entrapped in cationic didodecyldimethylammonium bromide (DDAB) surfactant films cast on vitreous‐carbon electrodes, in neutral aqueous solution. This was achieved by using for the first time the electrochemical impedance spectroscopy (EIS) measurements. This allows providing further insights in the electrical properties of these biofilms. The electroassisted catalytic reduction of molecular oxygen by the entrapped Hb, in neutral aqueous solution was also investigated. A catalytic current was observed close to the Fe(III)/Fe(II) redox potential of the immobilized Hb, and the intensity of the voltammetric cathodic peak (measured by cyclic voltammetry) is directly proportional to oxygen partial pressure. The influence of oxygen partial pressure on the impedance response of the films was also analyzed. The obtained results emphasizes the fact that the total charge transfer resistance of the modified electrode decreases with increasing oxygen partial pressure. A preliminary explanation of such an observation is discussed.     

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.     

Impedance spectroscopy analysis in a complex system: Sodium dodecyl sulfate solutions

Impedance measurements in the range 10–10⁷ Hz were carried out in water solutions of sodium dodecyl sulfate for concentrations below and above critical micellar concentration (cmc). The results were analysed using a series combination of two Voigt units, describing bulk and interface process and, additionally, an unexpected inductive one, problably due to inertial effects of an adsorbed layer of SDS molecules at the electrode. The interface processes, including the inductive one, show transition at a concentration somewhat below cmc.     

Electrochemical pressure impedance spectroscopy for investigation of mass transfer in polymer electrolyte membrane fuel cells

Mass transfer phenomena in membrane fuel cells are complex and diversified because of the presence of complex transport pathways including porous media of very different pore sizes and possible formation of liquid water. Electrochemical impedance spectroscopy, although allowing valuable information on ohmic phenomena, charge transfer and mass transfer phenomena, may nevertheless appear insufficient below 1 Hz. Use of another variable, that is, back pressure, as an excitation variable for electrochemical pressure impedance spectroscopy is shown here a promising tool for investigations and diagnosis of fuel cells.     

Detection of Listeria Monocytogenes by Electrochemical Impedance Spectroscopy

Listeria monocytogenes is detected by electrochemical impedance spectroscopy using a mouse monoclonal antibody immobilized onto an Au electrode. This yields sensitivities of 0.825 kΩ cm²/(CFU/mL) and 1.129 kΩ cm²/(CFU/mL) and detection limits of 5 CFU/mL and 4 CFU/mL for ideal solutions and filtered tomato extract, respectively. Control experiments with an Au electrode onto which a mouse monoclonal antibody to GAPDH is immobilized demonstrate that non‐specific adsorption is insignificant for the system and methodology studied here. Control experiments with Salmonella enterica demonstrate no cross‐reactivity to this food pathogen. Potential technological hurdles to development of a multiplexed impedance biosensor for food pathogens are also discussed.     

检测禽流感H5亚型病毒的阻抗型免疫研究

研制了一种可用于H5亚型禽流感病毒快速检测的阻抗型免疫传感器。通过蛋白A将H5N1表面抗原血凝素(HA)的单克隆抗体固定于金叉指阵列微电极表面,并与待测溶液中的目标抗原H5N1进行免疫反应。在[Fe(CN)6]3"/4"溶液中进行电化学阻抗谱扫描,表征电极的表面修饰及抗原捕获过程。当H5N1病毒浓度在21～26 HA unit/50μL范围时,其浓度的对数值与叉指阵列微电极的电子传递阻抗的变化值呈线性关系,相关系数为0.9885;检出限为20 HA unit/50μL,检测时间为1 h。此传感器特异性好,灵敏度高,可以重复使用,在病原微生物快速检测领域具有良好的应用前景。     

环氧树脂涂覆LY12铝合金在NaCl溶液中的阻抗模型

分别研究了裸LY12铝合金及涂覆环氧树脂涂层后合金在3.5％NaCl溶液中的电化学阻抗谱（EIS）.结果表明,LY12铝合金在点蚀电位以下阻抗谱上出现两个容抗弧,高频段对应Cl－参与的成膜阻抗,低频段对应铝阳极溶解的电化学反应阻抗.合金发生点蚀后出现低频感抗弧.合金/电极在NaCl溶液中先发生涂层吸水,当水及O2抵达基体后建立起电化学反应界面,合金遭受腐蚀；受涂层阻挡的影响,腐蚀产物的扩散逐渐成为控制步骤；当扩散速度较慢的Cl－抵达涂层/金属界面后,与界面处聚集的腐蚀产物间发生化学反应,完成成膜过程,阻抗谱上出现盐膜的阻抗,而扩散阻抗消失.提出了不同浸泡失效阶段涂层电极体系的阻抗模型.     

An Impedance Molecularly Imprinted Sensor for the Detection of Bovine Serum Albumin (BSA) Using the Dynamic Electrochemical Impedance Spectroscopy

A molecularly imprinted electrochemical sensor is successfully developed to detect bovine serum albumin (BSA) based on the dynamic electrochemical impedance spectroscopy (DEIS) instead of the traditional impedance spectroscopy. The sensor is prepared using chitosan and pyrrole as modified material and functional monomers, respectively, and the fast and real‐time characterization of molecular imprinting process can be obtained by DEIS. It is indicated that the removal and rebinding processes of BSA are closely related with the DEIS impedance under dynamic conditions, and the direct correlation between the resulting kinetic information and BSA concentrations can be established. As a result, the impedance changing rates in the initial 5 min of BSA adsorption are linear to the BSA concentrations ranging from 0.0001 to 0.01 ng mL^?1 and 0.01 to 1 ng mL^?1 with a detection limit of 5×10^?5 ng mL^?1 (S/N=3). In addition, the detection of BSA by DEIS does not require the system to be in equilibrium. The sensor also shows simplicity, high sensitivity, good stability and acceptable recovery in real samples, indicating its promising prospects in the fast and real‐time detection of proteins.     

A study of the electrical behaviour of isolated tomato cuticular membranes and cutin by impedance spectroscopy measurements

Different isolated tomato fruit cuticular membranes (ripe and green tomato cuticles and the cutin of these membranes) were studied by impedance spectroscopy measurements when the membranes were in contact with NaCl solutions at different concentrations. Remarkable differences in the impedance plots and the equivalent circuits associated to each membrane sample were obtained: the ripe tomato cuticle and the cutin, only present a relaxation process, but for the green tomato cuticle two relaxation processes were obtained. Using the equivalent circuits as models, electrical and electrochemical parameters for each membrane were determined. These results permit us to assign the relaxation processes to the different components of the tomato membrane (polyester matrix, carbohydrates and pigments), obtaining in this way a detailed picture of the different environments of the plant interface. Variation with NaCl concentration for the different electrical parameters was also studied, and the electrical resistance of the biopolymer matrix was obtained.