Interdigitated Microelectrode Array Research Articles

Electrical dual-sensing method for real-time quantitative monitoring of cell-secreted MMP-9 and cellular morphology during migration process.

MMP-9 (92 kDa gelatinease), which is member of matrix metalloproteinases (MMPs) family, plays a crucial role in the breakdown of extracellular matrix (ECM) by degrading the major components of ECM that lead to tumor cell invasion and metastasis through the basement membrane. Our study presents the on-chip dual-sensing device for rapid detection of cell-secreted MMP-9 and corresponding cell morphology changes in real-time domain. The device consists of 2 sensing platforms (both are interdigitated array microelectrodes - IDAMs) within 1 common fluidic chamber: one detects the cell morphology responses via Electric Cell-substrate Impedance Sensing (ECIS) technique, meanwhile the other records the cleavage effect between cell-secreted MMP-9 and the surface immobilized peptide via the capacitance-based sensing method. Thanks to the selectivity of designed peptide, this approach allows the rapid and specific detection of MMP-9. In comparison with gold standard ELISA assay, the detection time was significantly reduced from over 4h to within 30 min with the wide detection range from 10 pM to 10nM. Finally, this study provides the novel model for MMP-9 protease direct detection from living cell and new insights in multi-purpose detection of cancer associated enzyme and cell migration behavior.

A sensitive impedance biosensor based on immunomagnetic separation and urease catalysis for rapid detection of Listeria monocytogenes using an immobilization-free interdigitated array microelectrode.

In this study, we described a novel impedance biosensor combining immunomagnetic separation with urease catalysis for sensitive detection of foodborne bacteria using Listeria monocytogenes as model and an immobilization-free microelectrode as detector. The monoclonal antibodies (MAbs) were immobilized on the surface of the magnetic nanoparticles (MNPs) with the diameter of 180 nm by biotin-streptavidin system for specifically and efficiently separating Listeria cells from sample background. The polyclonal antibodies (PAbs) and the urease were modified onto the surface of the gold nanoparticles (AuNPs) with the diameter of 20 nm and the modified AuNPs were used to react with Listera to form the MNP-MAb-Listeria-PAb-AuNP-urease sandwich complexes. The urease in the complexes could catalyze the hydrolysis of the urea into ammonium carbonate and this led to an increase in the ionic strength of the media, which could be detected by the microelectrode. The magnetic separation efficiencies for L. monocytogenes at the concentrations ranging from 3.0×10(1) to 3.0×10(4) CFU/mL were over 95% for the pure cultures and over 85% for the spiked lettuce samples. The lower detection limit of this biosensor for L. monocytogenes was found to be 300 CFU/mL in both the pure cultures and the spiked lettuce samples. The microelectrode was demonstrated to be reusable for over 50 times with thorough cleaning by deionized water. This biosensor showed its potential to provide a simple, low-cost and sensitive method for rapid screening of foodborne pathogens and could be extended for detection of other biological or chemical targets.

Electrical impedance sensor for quantitative monitoring of infection processes on HCT-8 cells by the waterborne parasite Cryptosporidium

Cryptosporidium is the main origin of worldwide waterborne epidemic outbreaks caused by protozoan parasites. Its resilience to water chemical treatments and the absence of therapy led to consider it as a reference pathogen to assess water quality and as a possible bioterrorism agent. We here show that an electrical impedance-based device is able to get insights on Cryptosporidium development on a cell culture and to quantify sample infectivity. HCT-8 cells were grown to confluency on Interdigitated Microelectrode Arrays (IMA's) during 76h and then infected by Cryptosporidium parvum during 60h. The impedimetric response was measured at frequencies ranging from 100Hz to 1MHz and a 7min sampling period. As the infection progresses the impedance signal shows a reproducible distinct succession of peaks at 12h post infection (PI), 23h PI and 31h PI and local minima at 9h PI, 19h PI and 28h PI. An equivalent circuit modeling-based approach indicates that these features are mostly originated from paracellular pathway modifications due to host–parasite interactions. Furthermore, our data present for the first time a real-time monitoring of early parasitic stage development with alternating zoite and meront predominances, observed respectively at peaks and local minima in the impedimetric signal. Finally, by quantifying the magnitude of the impedimetric response, we demonstrate this device can also be used as an infectivity sensor as early as 12h PI thus being at least 6 times faster than other state of the art techniques.

Construction and Application of a Novel Impedance Sensor for Siderophore

Siderophore is a potential biomarker for pathogen diagnosis. In this study, a siderophore impedance sensor was constructed based on the formation of a siderophore-hemin complex prepared by modification of hemin on an interdigitated array microelectrode. Siderophore reacted with hemin and formed a complex on the electrode surface. As the conductivity of hemin was higher than that of siderophore, the formation of the complex led to decrease of conductivity on electrode surface which was measured by electrochemical impedance spectroscopy. The impedance change of constructed sensor was linear with the concentration of siderophore between 1 nM and 100 µM, with a limit of detection of 0.86 nM. The detection time was less than 15 min. When the sensor was used to analyze medium, the recovery was between 86.7% and 102.8%. Compared with conventional methods for siderophore, this approach is faster, more sensitive, and has potential application for the determination of pathogens.

Electrical impedance characterization of cell growth on interdigitated microelectrode array.

Electrical cell-substrate impedance sensing is a method for label-free and real-time monitoring of biological cells, which has been increasingly employed in the diagnostic and pharmaceutical industries. In this study, we fabricated an interdigitated electrode (IDE) array, which consists of 10 fingers, with a length of 1.2 mm, width of 50 μm, spacing of 50 μm, and thickness of 75 nm. The impedance spectra of the fabricated IDE were measured without or with cells in the frequency range of 100 Hz to 100 kHz using a lock-in amplifier based system and characterized by equivalent circuit modelling. Regarding the total impedance as a series resistance (R) and capacitance (C) model, R and C parameters were traced at a selected frequency during cell growth. It was able to monitor cell adherence and proliferation dependent on the behaviours and characteristics of cells on the fabricated IDE array by monitoring RC parameters. The degree of changes in RC value during cell growth was dependent on the type of cells used.

Electron Transport through Early Exponential‐Phase Anode‐Grown Geobacter sulfurreducens Biofilms

AbstractGeobacter sulfurreducens biofilms were grown to early exponential phase (i.e. the point at which the catalytic current first begins to increase) on interdigitated microelectrode arrays (IDAs), resulting in the formation of sparse cell clusters surrounded by extracellular polymeric substance (EPS). Continuous domains of EPS (defined here to include extracellular materials including filaments), but not cell clusters, were observed to bridge the gaps between adjacent electrode bands. Electrochemical gate measurements revealed electrical continuity between adjacent IDA electrode bands, indicating that extracellular electron transport (EET) occurs through the EPS. The dependency of the source‐drain current on the gate potential is peak shaped, which is consistent with EPS acting as a redox conductor. The gate potential at which the maximum source‐drain current occurs is approximately 0.13 V more positive than that for stationary‐phase biofilms, indicating that redox cofactors involved in EET at the early exponential phase are different to those at the stationary phase.

Indirect Voltammetric Sensing Platforms For Fluoride Detection on Boron-Doped Diamond Electrode Mediated via [FeF6]3− and [CeF6]2− Complexes Formation

Very simple and sensitive electroanalytical technique based on synergistic combination of reaction electrochemistry (specificity) and bare boron-doped diamond electrode (sensitivity) for the detection of fluorides in drinking water was developed as variant based on dynamic electrochemistry to ISE analysis. It is based on the formation of electroinactive fluoride complexes with Fe(III) and Ce(IV) ions decreasing such diffusion current of free metal on boron-doped diamond electrode. Due to low background signal of boron-doped diamond electrode reasonably low detection limits of the order of 10−6molL−1 for linear sweep voltammetric method using formation of [FeF6]3− and 10−7molL−1 in a square-wave variant of this technique have been achieved. This is approximately 1–2 orders lower than in the case of platinum comb-shaped interdigitated microelectrode array. Linear sweep voltammetric method based on [CeF6]2− complex formation has lower sensitivity and may be suitable for samples with higher content of fluoride and not to analysis of drinking water.

Design principles of co-planar interdigitated microelectrode arrays for solid-state ionic devices

Comprehensive analyses on the complex ion transport of co-planar interdigitated microelectrode arrays in solid-state ionic devices were carried out using finite element and analytical methods. We found that the ion flux between anode and cathode was constricted on the edges of both electrodes. Based on these results, we defined/analyzed the effective length and ohmic area-specific-resistance of various cell configurations (i.e., electrode width and electrolyte thickness). Using the relation between the effective length and the ohmic area-specific-resistance, we found an analytical model having favorable agreement with the finite element results and propose design rules for high-performance and densely integrated devices.

An impedance immunosensor based on low-cost microelectrodes and specific monoclonal antibodies for rapid detection of avian influenza virus H5N1 in chicken swabs.

Early screening of suspected cases is the key to control the spread of avian influenza (AI) H5N1. In our previous studies, an impedance biosensor with an interdigitated array microelectrode based biochip was developed and validated with pure AI H5 virus, but had limitations in cost and reliability of the biochip, specificity of the antibody against Asian in-field H5N1 virus and detection of H5N1 virus in real samples. The purpose of this study is to develop a low-cost impedance immunosensor for rapid detection of Asian in-field AI H5N1 virus in chicken swabs within 1h and validate it with the H5N1 virus. Specific monoclonal antibodies against AI H5N1 virus were developed by fusion of mouse myeloma cells with spleen cells isolated from an H5N1-virus-immunized mouse. Dot-ELISA analysis demonstrated that the developed antibodies had good affinity and specificity with the H5N1 virus. The microelectrodes were redesigned with compact size, fabricated using an improved wet-etching micro-fabrication process with a higher qualified production rate of 70-80%, and modified with the antibodies by the Protein A method. Equivalent circuit analysis indicated that electron transfer resistor was effective with the increase in impedance after capturing of the H5N1 viruses. Linear relationship between impedance change and logarithmic value of H5N1 virus at the concentrations from 2(-1) to 2(4) HAU/50 μl was found and the lower limit of detection was 2(-1) HAU/50 μl. No obvious interferences from non-target viruses such as H6N2, H9N2, Newcastle disease virus, and infectious bronchitis virus were found. Chicken swab tests showed that the impedance immunosensor had a comparable accuracy with real-time RT-PCR compared to viral isolation.

Modeling and Simulation of Enzymatic Biofuel Cells with Three-Dimensional Microelectrodes

The enzymatic biofuel cells (EBFCs) are considered as an attractive candidate for powering future implantable medical devices. In this study, a computational model of EBFCs based on three-dimensional (3-D) interdigitated microelectrode arrays was conducted. The main focus of this research is to investigate the effect of different designs and spatial distributions of the microelectrode arrays on mass transport of fuels, enzymatic reaction rate, open circuit output potential and current density. To optimize the performance of the EBFCs, numerical simulations have been performed for cylindrical electrodes with various electrode heights and well widths. Optimized cell performance was obtained when the well width is half of the height of the 3-D electrode. In addition, semi-elliptical shaped electrode is preferred based on the results from current density and resistive heating simulation.

Acetylcholinesterase biosensor for carbaryl detection based on interdigitated array microelectrodes.

In this study, an acetylcholinesterase (AChE) biosensor with superior accuracy and sensitivity was successfully developed based on interdigitated array microelectrodes (IAMs). IAMs have a series of parallel microband electrodes with alternating microbands connected together. Chitosan was used as the enzyme immobilization material, and AChE was used as the model enzyme for carbaryl detection to fabricate AChE biosensor. Electrochemical impedance spectroscopy was used in conjunction with the fabricated biosensor to detect pesticide residues. Based on the inhibition of pesticides on the AChE activity, using carbaryl as model compounds, the biosensor exhibited a wide range, low detection limit, and high stability. Moreover, the biosensor can also be used as a new promising tool for pesticide residue analysis.

Development of an aptamer-based impedimetric bioassay using microfluidic system and magnetic separation for protein detection

An aptamer-based impedimetric bioassay using the microfluidic system and magnetic separation was developed for the sensitive and rapid detection of protein. The microfluidic impedance device was fabricated through integrating the gold interdigitated array microelectrode into a flow cell made of polydimethylsiloxane (PDMS). Aptamer modified magnetic beads were used to capture and separate the target protein, and concentrated into a suitable volume. Then the complexes were injected into the microfluidic flow cell for impedance measurement. To demonstrate the high performance of this novel detection system, thrombin was employed as the target protein. The results showed that the impedance signals at the frequency of 90kHz have a good linearity with the concentrations of thrombin in a range from 0.1nM to 10nM and the detection limit is 0.01nM. Compared with the reported impedimetric aptasensors for thrombin detection, this method possesses several advantages, such as the increasing sensitivity, improving reproducibility, reducing sample volume and assay time. All these demonstrate the proposed detection system is an alternative way to enable sensitive, rapid and specific detection of protein.

Interdigitated Microelectrode Arrays Integrated in Microfluidic Cell for Biosensor Applications

In this work we present an approach for the use of phages as bioreceptors for bacteria detection in a microfluidic cell by Electrochemical Impedance Spectroscopy (EIS). With this aim, the biocomponent has been immobilized on interdigitated gold microelectrodes with the phyisorption technique. The three electrodes (reference electrode, counter electrode and work electrode) are integrated on the same chip and a microfluidic cell is used. We have shown that chip is stable in liquid medium for several hours. For the detection side, the interaction of E.coli bacteria with T4 phages shows an increase of the impedance. A detection limit of 103 CFU mL-1 was obtained with good reproducibility.

Hygroscopic Particle Behavior Studied by Interdigitated Array Microelectrode Impedance Sensors

The hygroscopic behavior of soluble salts bears importance in many research fields including atmospheric sciences, corrosion, porous building materials, and pharmaceuticals. Several methods have been used to study deliquescence (solid to liquid) and efflorescence (liquid to solid) phase transitions of these salts. In this study, we measured the deliquescence and efflorescence RH values of single salt microparticles deposited on an interdigitated microelectrode sensor via electrical impedance. The salts examined were NaCl, LiCl, NaBr, KCl, and MgCl2. Measured values were in agreement with in situ optical microscopic observations and, with the exception of MgCl2, literature values. In the case of MgCl2, deliquescence occurred at 33% RH and 12-15% RH, with the latter range being previously unreported. The depressed deliquescence RH was hypothesized to be a result of the formation of a metastable MgCl2 hydrate. Incomplete efflorescence of MgCl2 was also observed after exposure to <1.5% RH for up to 22 h due to formation of solid shells which trapped fluid. The phenomena elucidated by these results provide an explanation for the anomalous water retention and uptake behavior of MgCl2 below 33% RH reported elsewhere in the literature. The results presented in this study validate the use of this method as an alternative or complementary method for study of bulk-phase transitions of substrate-deposited particles across a broad RH range. These findings also demonstrate the utility of this method for detection of fluid trapping which cannot be directly ascertained by gravimetric and line-of-sight techniques commonly used in the study of hygroscopic particles.

In situ fluorimetric detection of micrometer-scale pH gradients at the solid/liquid interface

In this study, we describe the development of a sensing system for the real-time analysis of the pH and pH gradients at the solid/liquid interface. A pH-sensitive fluorescent platform has been developed by ‘clicking’ an alkyne-modified N-methylpiperazine naphthalimide onto an azide monolayer on glass. The surface immobilisation of the molecular probe was assessed by X-ray photoelectron spectroscopy, while sensitivity and reversibility were demonstrated by fluorescence microscopy and contact angle goniometry. The pH titration of the platform allowed for the determination of the pKa value of the pH-sensitive probe at the solid/liquid interface. The platform was employed for the real-time interfacial analysis of micron-scale pH gradients at the solid/liquid interface induced by the electrolysis of water as exerted by an interdigitated microelectrode array. The calibration by the platform titration allowed the visualisation and quantification of the pH gradient with a dynamic range of about three pH units and a sub-second temporal resolution.

Optimization of planar interdigitated microelectrode array for biofluid transport by AC electrothermal effect

Point-of-care (POC) diagnostics is one of the most important applications for microfluidic research. However, the development of microfluidic POC devices needs to overcome great obstacles to reach market. One challenge is to find a chip-scale pumping strategy that is of low cost, small size, and light weight. Because of their simple implementation, electrokinetic techniques have been extensively investigated as a promising candidate for realizing disposable pumps, with the majority of research effort focusing on direct current and alternating current (AC) electroosmosis. As POC applications often need to handle conductive biofluids with medium to high salt content, AC electrothermal (ACET) effect has been investigated recently for pumping of biofluids, albeit with less than desirable pumping performance. In order to achieve effective on-chip ACET micropumps, this paper presents one of the first efforts in optimizing ACET micropump design utilizing planar interdigitated electrodes. The effects of electrode dimensions on pumping rate were numerically studied using COMSOL Multiphysics and MATLAB, and an optimal ratio of electrode geometry was found for various pumping scenarios. The optimal geometry ratio was tested to be valid over a wide range of electrode characteristic lengths, AC signals, and fluid ionic strengths. Experimental validation of the simulation results was also conducted, and higher flow velocities over prior reports were consistently demonstrated by optimized electrode arrays.

Sol–gel immobilized enzymatic glucose biosensor on gold interdigitated array (IDA) microelectrode

An enzymatic glucose biosensor with good sensitivity, selectivity and stability employing interdigitated array microelectrode (IDA μ-electrode) was reported. IDA μ-electrode was prepared by photolithography method with its surface immobilized with a layer of glucose oxidase (GOx), entrapped in a three-dimensional network composed of chitosan and tetraethyl orthosilicate sol–gel. The surface of the as-prepared IDA μ-electrode was characterized by scanning electron microscope, electron spectroscopy for chemical analysis, and atomic force microscopy. The experimental parameters for the best glucose sensing performance were optimized according to the loading of GOx, the applied voltages, the concentration of mediator, and the pH for glucose detection. The resulted biosensor exhibited a good response to glucose with a wide linear range from 0 to 35 mM and a low detection limit of 1 mM. The glucose sensor also showed a short response time (within 5 s) that the fast response was reflected by the small Michaelis–Menten constant (KM app) with a value of 2.94 mM. The reported glucose biosensor exhibited good sensitivity (8.74 μA/mM.cm2), reproducibility, and stability.

3D stepped electrodes on a flexible substrate with permanently bonded poly(dimethylsiloxane) channels for moving microfluid

Interdigitated microelectrode arrays have been exploited to move electrolyte via ac electro-osmosis. The performance of three dimensional (3D) stepped electrodes has been shown to exceed that of planar electrodes. However, to date all prototypes described have been based on solid silicon or glass substrates, limiting the usage of such devices. This report, to our best knowledge, is the first to describe a 3D stepped microelectrode array on a flexible Kapton® substrate. The Kapton surface was modified to make it capable of bonding with poly(dimethylsiloxane) microchannels. The metal electrode was patterned by wet etching, a simpler process than previous approaches. Results of bonding, bending, and fluidic testing are reported. The frequency response obtained using deionized water showed maximum velocities of approximately 370 and 180 μm/s at 5Vpp for testing with a flat and bent substrate, respectively.

3D Dendritic Nanostructure of Silver‐Array: Preparation, Growth Mechanism and Application in Nitrate Sensor

AbstractA 3D dendritic nanostructure of silver‐array (DSA) was prepared via electrodeposition on an interdigitated array (IDA) microelectrode. For preparation of this nanostructure, the optimal parameters such as deposition potential, deposition time, the electrode bandwidth and gap size were systematically investigated. It was found that the edge effect of the IDA microelectrode is a key factor for controlling the 3D dendritic growth of silver. Furthermore, the formation of the 3D dendritic morphology was discussed from the aspect of electrochemical nucleation theory and nonequilibrium growth dynamics to give a deep understanding of its growth mechanism. For its potential practical application, we showed that the as‐prepared 3D DSA nanomaterial exhibited high electrocatalytic reduction ability to nitrate in neutral solution and excellent performance for nitrate determination. An amperometric nitrate microsensor based on the 3D DSA was obtained.

Rapid Detection of Avian Influenza Virus Using Immunomagnetic Separation and Impedance Measurement

An interdigitated array microelectrodes (IDAMs) based impedance biosensor in combination with immunomagnetic separation was developed for rapid detection of avian influenza virus (AIV) subtype H5. Streptavidin-coated magnetic nanobeads were immobilized onto the biotin-labeled anti-H5 monoclonal antibodies to capture AIV H5 (e.g., H5N1) from sample solutions by the specific immunoreaction and form antibodies coated nanobeads-AIV complexes. Then these complexes were separated and concentrated by a magnetic field and the impedance magnitude was measured by IDAMs in a frequency range from 20 Hz to 1 MHz. The sensitivity and specificity of this biosensor were investigated. The biosensor could detect as few as 2-1 HA unit/50 μl of inactivated AIV H5N1. A linear relationship between the change of impedance magnitude and the logarithmic value of AIV H5N1 concentration was found in the range of 2-1 to 24 HA unit/50 μl. Non-target viruses, such as AIV subtype H1 and Newcastle disease virus, could not induce detectable signals. Equivalent circuit analysis showed that the medium resistance was responsible for the impedance change caused by the presence of AIV H5N1. The whole detection process from sampling to impedance measurement was able to be completed within 1.5 h.