Interdigitated Microelectrodes Research Articles

Flexible and high-performance microsupercapacitors with wide temperature tolerance

The development of miniaturized and wearable electronics has triggered an urgent demand for microsupercapacitors (MSs) with high performance, reliable safety and flexibility. However, very few studies have examined the operating performance of MSs at temperatures other than room temperature due to the poor temperature tolerance of conventional polyvinyl alcohol (PVA)-based electrolytes. Herein, a novel class of high-performance flexible MSs has been developed through covering a highly conductive graphene oxide/polyacrylamide (GO-PAA) polyelectrolyte on interdigital microelectrodes of polyimide-tape-supported carbon nanotube/worm-like-structured polyaniline nanofibers patterned by laser direct writing. These polyelectrolyte-based microsupercapacitors (PMSs) show the widest temperature tolerance from −30 °C to 100 °C among all reported MSs, delivering record high areal energy densities and capacitances at −30 °C (7.48 μWh cm−2 and 84.4 mF cm−2) and 100 °C (8.55 μWh cm−2 and 96.2 mF cm−2). In comparison, PMSs possess over seven times higher specific capacitance than MSs based on current PVA/H2SO4 electrolyte at −30 °C and 100 °C. Additionally, PMSs also exhibit high safety, excellent cycling stability (94.2% capacitance retention after 8000 cycles even at −30 °C) as well as superior flexibility.

Confined 1D Propulsion of Metallodielectric Janus Micromotors on Microelectrodes under Alternating Current Electric Fields.

There is mounting interest in synthetic microswimmers ("micromotors") as microrobots as well as a model system for the study of active matters, and spatial navigation is critical for their success. Current navigational technologies mostly rely on magnetic steering or guiding with physical boundaries, yet limitations with these strategies are plenty. Inspired by an earlier work with magnetic domains on a garnet film as predefined tracks, we present an interdigitated microelectrodes (IDE) system where, upon the application of AC electric fields, metallodielectric (e.g., SiO2-Ti) Janus particles are hydrodynamically confined and electrokinetically propelled in one dimension along the electrode center lines with tunable speeds. In addition, comoving micromotors moved in single files, while those moving in opposite directions primarily reoriented and moved past each other. At high particle densities, turbulence-like aggregates formed as many-body interactions became complicated. Furthermore, a micromotor made U-turns when approaching an electrode closure, while it gradually slowed down at the electrode opening and was collected in large piles. Labyrinth patterns made of serpentine chains of Janus particles emerged by modifying the electrode configuration. Most of these observations can be qualitatively understood by a combination of electroosmotic flows pointing inward to the electrodes, and asymmetric electrical polarization of the Janus particles under an AC electric field. Emerging from these observations is a strategy that not only powers and confines micromotors on prefabricated tracks in a contactless, on-demand manner, but is also capable of concentrating active particles at predefined locations. These features could prove useful for designing tunable tracks that steer synthetic microrobots, as well as to enable the study of single file diffusion, active turbulence, and other collective behaviors of active matters.

General Interfacial Self-Assembly Engineering for Patterning Two-Dimensional Polymers with Cylindrical Mesopores on Graphene.

Free-standing 2D porous nanomaterials have attracted considerable interest as ideal candidates of 2D film electrodes for planar energy storage devices. Nevertheless, the construction of well-defined mesopore arrays parallel to the lateral surface, which facilitate fast in-plane ionic diffusion, is a challenge. Now, a universal interface self-assembly strategy is used for patterning 2D porous polymers, for example, polypyrrole, polyaniline, and polydopamine, with cylindrical mesopores on graphene nanosheets. The resultant 2D sandwich-structured nanohybrids are employed as the interdigital microelectrodes for the assembly of planar micro-supercapacitors (MSCs), which deliver outstanding volumetric capacitance of 102 F cm-3 and energy density of 2.3 mWh cm-3 , outperforming most reported MSCs. The MSCs display remarkable flexibility and superior integration for boosting output voltage and capacitance.

General Interfacial Self‐Assembly Engineering for Patterning Two‐Dimensional Polymers with Cylindrical Mesopores on Graphene

AbstractFree‐standing 2D porous nanomaterials have attracted considerable interest as ideal candidates of 2D film electrodes for planar energy storage devices. Nevertheless, the construction of well‐defined mesopore arrays parallel to the lateral surface, which facilitate fast in‐plane ionic diffusion, is a challenge. Now, a universal interface self‐assembly strategy is used for patterning 2D porous polymers, for example, polypyrrole, polyaniline, and polydopamine, with cylindrical mesopores on graphene nanosheets. The resultant 2D sandwich‐structured nanohybrids are employed as the interdigital microelectrodes for the assembly of planar micro‐supercapacitors (MSCs), which deliver outstanding volumetric capacitance of 102 F cm−3 and energy density of 2.3 mWh cm−3, outperforming most reported MSCs. The MSCs display remarkable flexibility and superior integration for boosting output voltage and capacitance.

Investigations of the humidity sensing properties of side-chain-type sulfonated poly (arylene ether ketone)s

Side-chain-type sulfonated poly (arylene ether ketone)s containing naphthalene moieties with a degree of sulfonation (Ds) from 0.2 to 1.9 were synthesized. Humidity sensors were fabricated by cast coating on silver–palladium interdigital microelectrodes. The properties of this series of materials in terms of water absorption, glass transition temperature, and humidity sensing were characterized in detail. The investigations on the humidity sensing performance showed that with the increase in the Ds, the hysteresis of our materials exhibits an increasing trend first, followed by a decrease. This special phenomenon has not been reported before and caught our attention. From the results of humidity sensing properties, among the materials, the one with 0.2 Ds is promising for applications in humidity sensing due to its small hysteresis and fast response to varied relative humidity (RH). For a better understanding of the humidity sensing behavior of the sensor, complex impedance spectra were also measured. In the long-term stability measurement, the deviation of the measured impedance of the sensor at 97% RH is not obvious, proving good stability in a humid environment.

Amyloid beta in nasal secretions may be a potential biomarker of Alzheimer\u2019s disease

We investigated the level of amyloid beta (Aβ) in nasal secretions of patients with Alzheimer’s disease dementia (ADD) using interdigitated microelectrode (IME) biosensors and determined the predictive value of Aβ in nasal secretions for ADD diagnosis. Nasal secretions were obtained from 35 patients with ADD, 18 with cognitive decline associated with other neurological disorders (OND), and 26 cognitively unimpaired (CU) participants. Capacitance changes in IMEs were measured by capturing total Aβ (ΔCtAβ). After 4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid (EPPS) was injected, additional capacitance changes due to the smaller molecular weight Aβ oligomers disassembled from the higher molecular weight oligomeric Aβ were determined (ΔCoAβ). By dividing two values, the capacitance ratio (ΔCoAβ/ΔCtAβ) was determined and then normalized to the capacitance change index (CCI). The CCI was higher in the ADD group than in the OND (p = 0.040) and CU groups (p = 0.007). The accuracy of the CCI was fair in separating into the ADD and CU groups (area under the receiver operating characteristic curve = 0.718, 95% confidence interval = 0.591–0.845). These results demonstrate that the level of Aβ in nasal secretions increases in ADD and the detection of Aβ in nasal secretions using IME biosensors may be possible in predicting ADD.

Sensitivity enhancement in photoionization detector using microelectrodes with integrated 1D nanostructures

Photoionization detectors (PIDs) that use high-energy photons to ionize gas molecules have attracted considerable attention as volatile organic compound (VOC) sensors owing to their high sensitivity, selectivity, and reliability. Recently, miniaturized PIDs have been developed to further improve the sensing performance. However, most studies have focused solely on the miniaturization of the ionization chamber, although the electrode is an important factor for determining the sensitivity and operation voltage. This work demonstrates a PID composed of Si microelectrodes fabricated via microfabrication with one-dimensional (1D) nanostructures coated on them. The interdigitated microelectrodes offer a larger surface area capable of enhanced capturing of positively charged ions and electrons compared to typical mm-scale electrodes, resulting in the successful detection of 500 ppb toluene at an applied voltage of 0.2 V. Furthermore, taking advantage of the outstanding surface-to-volume ratio of 1D nanostructures, Ag nanowire-coated microelectrodes and carbon nanotube (CNT)-coated microelectrodes exhibit 38% and 76% improvement in sensitivity, respectively, than the bare Si microelectrodes. The CNT-coated microelectrodes show superior linearity and repeatability at toluene concentrations from 0.1 to 1.0 ppm. The proposed PID will be a promising candidate for portable VOC sensors.

Back Cover: A highly sensitive aptasensor for on‐site detection of lipopolysaccharides in food

DOI: 10.1002/elps.201800289 The cover picture shows a rapid, highly sensitive and specific aptasensor in one-pot single step format for lipopolysaccharides (LPS) detection. An interdigitated microelectrode (IDME) array modified with LPS-specific aptamer is used as the sensor. During detection, a special AC measuring signal is applied over the IDME digits. The AC signal serves two purposes simultaneously, attracting the target molecules towards the IDME via AC electrokinetic effects and capacitively monitoring topological changes at the IDME surface due to aptamer-LPS binding. The sensor can detect as low as 4.93 fg/mL LPS in 30 s.

Electrochemical detection of a P. polymyxa biofilm and CIP cleaning solutions by voltammetric microsensors

Biofilm formation in processing equipment can lead to higher costs due to more frequent cleaning events as well as the contamination of processed foods and is a concerning issue. It is necessary to establish new methods for the detection of biofilms formation on surfaces. The use of electrochemical microsensors for biofilm detection could be a strategy for real time biofilm control in processing equipment. In this study, voltammetric methods, cyclic voltammetry (CV) and square wave voltammetry (SWV), were employed to detect P. polymyxa biofilms and CIP cleaning solutions on platinum-based interdigitated ring array microelectrodes. The differences between the current responses of the uncovered sterile microelectrodes and the microelectrodes after Paenibacillus polymyxa attachment for 18 h were determined. The surface coverage of microelectrodes was visualized using microscopy techniques. The results of this study demonstrated that cyclic voltammetry revealed the most promising results for P. polymyxa biofilm detection, while square wave voltammetry can be recommended for the detection of CIP cleaning solutions.

Dielectrophoresis-based filtration effect and detection of amyloid beta in plasma for Alzheimer's disease diagnosis

The filtration effect improves the impedance change through specific binding of target molecules in plasma, and decreases this change by nonspecific binding of matrix factors in plasma (i.e., matrix effect). A difference in dielectrophoresis (DEP) forces applied to target molecules and matrix factors causes the filtration effect. An optimized DEP force affects target molecules, which remain in the reaction region of an interdigitated microelectrode (IME) sensor. Various matrix factors, which are larger than the target molecules, are influenced by a strong DEP force and are filtered out of the reaction region. To demonstrate the filtration effect, the matrix effect was confirmed in standard plasma and in phosphate-buffered saline, based on the detection of amyloid beta (Aβ), an Alzheimer's disease (AD)-associated peptide. The filtration effect was verified using the matrix effect factor (MEF), which was calculated from the impedance change values in different detection environments. In standard plasma, the MEF value decreased by approximately 78.12%, and in buffer with heterogeneous Aβ, by approximately 75.43%. Plasma from patients with AD and normal controls (NCs) was analyzed using the value of the impedance change by the filtration effect. The impedance change was enhanced approximately 1.52 ± 0.03-fold in AD plasma, but declined approximately 0.90 ± 0.03-fold in NC plasma. This difference tendency by the filtration effect was the disease evaluation index and used as an important criterion that distinguished between the AD and NC plasma. Plasma-based AD diagnosis may be possible, based on the filtration effect.

Ionic liquid pre-intercalated MXene films for ionogel-based flexible micro-supercapacitors with high volumetric energy density

Ionogel-based flexible micro-supercapacitors are constructed based on interdigital microelectrodes of ionic liquid pre-intercalated MXene compact films.

Screen-printing fabrication of high volumetric energy density micro-supercapacitors based on high-resolution thixotropic-ternary hybrid interdigital micro-electrodes

We demonstrate a general and scalable screen-printing technique for the one-step construction of high-performance micro-supercapacitors.

Scalable fabrication of high-performance micro-supercapacitors by embedding thick interdigital microelectrodes into microcavities

Micro-supercapacitors (MSCs) with thick interdigital microelectrodes of carbon-based materials exhibit excellent electrochemical performance and hold tremendous promise for applications in microscale energy storage devices. Here, a scalable strategy to fabricate thick embedded multiwalled carbon nanotubes (MWCNTs) as interdigital microelectrodes for MSCs has been developed and investigated. To this end, sufficient MWNCT inks are firstly cast onto pre-patterned microcavity surfaces and then more MWCNT materials are embedded into the microcavities by rapid solvent evaporation. After removal of residual materials from the surfaces by a doctor-blading process, thick interdigital MWCNT microelectrodes with heights up to 190 μm are obtained. These embedded microelectrodes simplify the device structure and improve the mechanical flexibility by acting as both active materials and current collectors. Using interdigital microelectrodes with a width of 250 μm and an interspace of 50 μm, the fabricated MSCs exhibit outstanding electrochemical performance with a high capacitance of 19.5 mF cm-2 and an energy density of 2.48 μW h cm-2 at a power density of 24.7 μW cm-2. On the other hand, four light emitting diodes (LEDs) are successfully powered by three series of MSCs, indicating that MSCs can be connected in series and parallel to yield suitable operating voltages and currents for practical applications.

Polystyrene-coated Interdigitated Microelectrode Array to Detect Free Chlorine towards IoT Applications.

We apply interdigitated microelectrode array (IDA) sensors for water quality monitoring. IDA sensors with an ion-sensitive coating show higher sensitivity of about 600 mV with the hypochlorite ion concentration increasing from 0 to 10 ppm more than the traditional sensing method. The response mechanism and selectivity have been studied. Several material components that affect the sensing process were explored. Coupling agents and plasticizer were introduced into the coating material to improve the coating material quality and its adhesion to the electrodes. The stability/repeatability and linearity have been significantly improved.

Efficacy and cardiotoxicity integrated assessment of anticancer drugs by a dual functional cell-based biosensor

Cancer significantly threatens human life, and the chemotherapy drugs are developed and widely used in the cancer treatment. However, the side effects of drugs on heart cause other serious problems. In this study, a dual functional cell-based biosensor integrating interdigitated electrodes (IDEs, monitoring cell viability) and microelectrodes (monitoring electrophysiology) is developed to comprehensively evaluate the efficacy and cardiotoxicity of anticancer drugs. Hela cells and cardiomyocytes of neonatal rats were cultured on this cell-based biosensor. Taxol (TAX) and vinblastine (VBL) were utilized to verify the performance of this platform. The efficacy of TAX and VBL were verified by comparing the results of traditional method and this method. As for cardiotoxicity, TAX showed little effect on cell viability, and slightly influenced the electrophysiological activity of cardiomyocytes at the range of 50–800 nM (with the sensitivity of -13.48%/lg TAX (nM) in field potential amplitude (FPA)) and 7.12%/lg TAX (nM) in firing rate (FR)). By contrast, VBL presented a relatively strong effect on both cell viability and electrophysiological activity of cardiomyocytes, which show a dose-dependent manner within a certain concentration range (with the sensitivity of -41.86%/lg VBL (nM) in FPA and -30.45%/lg VBL (nM) in FR). Owing to its simultaneously monitoring cell viability and electrophysiological activity of cells in a real-time and dynamic way, the dual functional cell-based biosensors will be a utility platform to evaluate the efficacy and cardiotoxicity of candidate compounds in new drug development.

Electron transfer during binding processes between thiolate molecules and Au nano-islands

We investigated electron transfer during the time-dependent binding processes between thiolate molecules and Au nano-islands by observing tunneling current with an interdigitated microelectrode supporting the sputtered Au nano-islands (IME@AuNI). The time-dependent optical and electrical signal variation during the binding process was examined for five kinds of thiolates. As the immersion time was prolonged, the optical absorbance increased, whereas the current passing through the IME@AuNI decreased. Importantly, the spectral and current characteristics depended on the thiolate structure, because of the formation of capping layer in accordance with thiolate structure. These results are mainly attributed to synergistic effects of electron transfer from Au nano-islands to thiolate molecules and bridging effects of thiolate molecules among Au nano-islands.

High-sensitivity and low-hysteresis humidity sensor based on hydrothermally reduced graphene oxide/nanodiamond

This paper demonstrated the preparation of reduced graphene oxide/nanodiamond (rGO/ND) nanocomposite by a facile hydrothermal reduction method and its application as an ultrahigh performance humidity sensor. The synthesized rGO/ND suspension was deposited on Au interdigitated microelectrodes for sensor fabrication. The nanostructures, morphologies, and composition properties of the prepared rGO/ND nanocomposite were characterized by scanning electron microscopy (SEM), atomic force microscope (AFM), Raman spectrum, and Fourier Transform infrared spectroscopy (FTIR). The experimental results demonstrated that the rGO/ND based humidity sensor exhibited an ultrahigh sensitivity (13,086 pF/%RH), which surpasses the existed conventional humidity sensors and is more than 30 times higher than that of the pure rGO and pure ND based humidity sensors. The hysteresis characteristic of rGO/ND based humidity sensor is also dramatically improved when compared with pure rGO and pure ND based humidity sensors. Meanwhile, the sensor shows a fast response/recovery time, excellent repeatability and good long-term stability. The humidity sensing mechanism was analyzed via complex impedance spectrum (CIS). Lastly, a sensing mechanism model was established to detailedly explain the improved hysteresis properties. This research revealed that rGO/ND composite film is a promising candidate material for fabricating a high-performance humidity sensor.

Electrochemical immunosensor utilizing electrodeposited Au nanocrystals and dielectrophoretically trapped PS/Ag/ab-HSA nanoprobes for detection of microalbuminuria at point of care

In this study, we have fabricated a simple disposable electrochemical immunosensor for the point of care testing of microalbuminuria, a well-known clinical biomarker for the onset of chronic kidney disease. The immunosensor is fabricated by screen-printing carbon interdigitated microelectrodes on a flexible plastic substrate and utilizes electrochemical impedance spectroscopy to enable direct and label free immunosensing by analyzing interfacial changes on the electrode surface. To improve conductivity and biocompatibility of the screen-printed electrodes, we have modified it with gold nanoparticles, which are electrodeposited using linear sweep voltammetry. To enable efficient immobilization of HSA antibodies, we have developed novel PS/Ag/ab-HSA nanoprobes (polystyrene nanoparticle core with silver nanoshells covalently conjugated to HSA antibodies), and these nanoprobes are trapped on the electrode surface using dielectrophoresis. Each immunosensor has two sensing sites corresponding to test and control to improve specificity by performing differential analysis. Immunosensing results show that the normalized impedance response is linearly dependent on albumin concentration in the clinically relevant range with good repeatability. We have also developed a portable impedance readout module that can analyze the data obtained from the immunosensor and transmit it wirelessly for cloud computing. Consequently, the developed immunosensing platform can be extended to the detection of a range of immunoreactions and shows promise for point of diagnosis and public healthcare monitoring.

Biocompatible Symmetric Na-Ion Microbatteries with Sphere-in-Network Heteronanomat Electrodes Realizing High Reliability and High Energy Density for Implantable Bioelectronics.

The prolonged life expectancy accelerates the development of implantable bioelectronic devices. However, conventional batteries with limited lifetime, rigid architecture, and inferior energy density greatly restrict their applications in patient's body. Herein, a novel flexible symmetric Na-ion microbattery based on the heteronanomat electrode and the biocompatible electrolyte has been developed. The film electrodes with sphere-in-network architecture are synthesized by simultaneously electrospinning and electrospraying followed by carbonization. The combined technologies allow a uniform incorporation of active materials/C spheres into the carbon nanofiber matrix, which results in the heteronanomat electrodes with robust structure, fast electron/ion transport, and compact mass loading. The flexible microbatteries are fabricated based on the interdigitated microelectrodes and the biocompatible electrolytes, which provides a new implantable power source for bioelectronics. As a proof-of-concept study, the symmetric sodium-ion microbatteries are constructed from the heteronanomat bifunctional electrodes (based on Na2VTi(PO4)3) and the biocompatible electrolyte. The high reversibility, fast kinetics, and high energy density of the symmetric system in the biocompatible electrolytes reveal their superior performance in bioenvironments. Moreover, the high capacity retention (over 98%) and the high stability of microbattery implanted in a living SD rat for a month further demonstrate its high reliability for long-term in vivo diagnosis. Therefore, this work not only presents a new sphere-in-net heteronanomat structure for fabricating high-performance electrode but also gives significant contributions to develop high-energy-density and high safety biocompatible power sources of implantable bioelectronics.

Reduced graphene oxide biosensor platform for the detection of NT-proBNP biomarker in its clinical range

Reduced graphene oxide (rGO) thin films can be exploited as highly sensitive transducer layers and integrated in interdigital micro-electrode systems for biosensing processes. The distinctive bipolar characterisitics of rGO thin films can be modulated by a very low external electric field due to the electrostatic charges of biomolecules. These charges lead to a fast response in the readout signals of rGO based ion sensitive field-effect transistors (ISFETs). The characterisitc changes of rGO ISFETs enable a fast, accurate and reproducible detection of biomolecules. The biosensing mechanism offers a fast and label-free approach for analyte detection in contrast to the classical ELISA method.In this contribution, we introduce a reproducible fabrication process of rGO based field-effect transistors on wafer level. The sensors are functionalized as biosensors to measure N-terminal pro-brain natriuretic peptide (NT-proBNP) in human serum within its clinical range. Our optimized rGO sensor shows very promising electrical properties and can be considered as a proof of concept study for the detection of various analytes. The easy and cost-effective fabrication as well as the versatile usability make this new technological platform an auspicious tool for different sensing applications in future.