Microstructured Electrodes Research Articles

Effective Method for Micro-Patterning Arene-Terminated Monolayers on a Si(111) Electrode.

Microstructured electrodes are significant to modern electrochemistry. A representative aromatic group, 4-ferrocenylphenyl one, was covalently bound to a micropatterned silicon electrode via the arylation of a hydrogen-terminated silicon(111) surface formed selectively on a Si wafer. Starting from a silicon(100)-on-insulator (SOI) wafer, the aromatic monolayer was attached sequentially by spin-coating a resist, electron beam lithography, Cr/Au deposition, lift-off, anisotropic etching with aqueous KOH solution, and Pd-catalyzed arylation. Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) are used to characterize the coupling reaction between 4-ferrocenyl group and silicon substrate, and to confirm performance of the final modified microsized electrode. These data show that this synthetic protocol gives chemically well-defined and robust functionalized monolayers on a silicon semiconducting surface with a small electrode.

The Capacitance of Nickel Pattern Electrodes on Zirconia Electrolyte

Micro-structured thin-film electrodes were employed to investigate the capacitive behavior of nickel on yttria-stabilized zirconia (YSZ) electrolytes by means of electrochemical impedance spectroscopy. Electrodes with different shapes and electrode areas clearly showed a linear relationship between capacitance and the electrode area. Electrostatic double layer models, however, could not explain the observed area specific capacitance value of ca. 3 F/m². This fact, the characteristic voltage dependence with a hysteresis, and the effect of H2S on the electrode capacitance indicate substantial contributions of a chemical capacitance. Possible types of chemical capacitance in the system Ni(H2/H2O)/YSZ are discussed and an oxygen partial pressure dependent mechanism change is suggested.

Fabrication of honeycomb-patterned polyaniline composite films containing cellulose triacetate with high conductivity and mechanical stability

Polyaniline (PANI) biocomposites were prepared via in situ polymerization of aniline monomer with cellulose triacetate (CTA) and by using ammonium persulfate as an initiator in an aqueous solvent. The composites exhibited high solubility in organic solvents due to the incorporated CTA component, and enabled the fabrication of honeycomb-patterned thin films by casting the PANI composite solutions under humid conditions. The honeycomb-patterned PANI–CTA composite films showed a high conductivity corresponding to about 1.5 S/cm, good mechanical stability, and high flexibility. The composites have a potential advantage comparing to pure PANI because of biodegradability and high solubility due to included CTA. These composite films can usefully be applied in the field of bio-nanotechnology and medicine including micro-structured electrode surfaces, filters for cell sorting, and bio-interfaces and so on. POLYM. COMPOS., 37:2649–2656, 2016. © 2015 Society of Plastics Engineers

Contact poling of Rb:KTiOPO(4) using a micro-structured silicon electrode.

A contact poling technique for domain engineering of ferroelectrics using a micro-structured silicon electrode is demonstrated on Rb:KTiOPO4. High quality QPM gratings were reproducibly fabricated. The silicon electrode is reusable and the technique potentially suitable when complex structures with sub-μm features are to be domain engineered, which otherwise is incompatible with conventional photolithography. A non-negligible domain broadening was seen and attributed to a low nucleation rate using this type of electrode. However, under the appropriate poling conditions, this could be exploited to obtain a QPM grating with a short pitch (2 μm), equal to half of the electrode period.

A micro-structured Si-based electrodes for high capacity electrical double layer capacitors

We challenged to make basis for Si electrodes of electric double layer capacitors (EDLC) used as a power source of micro-sensor nodes. Mcroelectromechanical systems (MEMS) processes were successfully introduced to fabricate micro-structured Si-based electrodes to obtain high surface area which leads to high capacity of EDLCs. Study of fundamental properties revealed that the microstructured electrodes benefit from good wettability to electrolytes, but suffer from electric resistance. We found that this problem can be solved by metal-coating of the electrode surface. Finally we build an EDLC consisting of Au-coated micro-structured Si electrodes. This EDLC showed capacity of 14.3 mF/cm2, which is about 530 times larger than that of an EDLC consisting of flat Au electrodes.

Prototyping of wrinkled nano-/microstructured electrodes for electrochemical DNA detection.

Biosensing platforms are ideal for addressing the diagnostic needs of resource-poor areas; however, the translation of such systems from the laboratory to the point-of-need has been a slow process. Rapid prototyping methods that enable an application-specific biosensor to be created in a matter of hours from design to fabrication would expedite the clinical and field testing of such systems. Here, we demonstrate a benchtop method based on craft cutting and polymer-induced wrinkling for creating multiplexed electrochemical DNA biosensors. This fabrication method allows multiscale wrinkled electrodes with features in the millimeter to nanometer length scales to be created in a matter of hours. These wrinkled electrodes display an enhanced surface area compared to planar electrodes and are shown to be structurally tunable by changing the film thickness. We demonstrate that structural tunability of these electrodes is translatable to functional tunability as the density of surface-immobilized probe molecules can be manipulated using wrinkled electrodes of different thicknesses. Furthermore, a simple proof-of-concept electrocatalytic DNA biosensor is demonstrated for distinguishing between complementary and noncomplementary oligonucleotides.

Electrochemical performance of laser micro-structured nickel oxyhydroxide cathodes

This study describes the preparation and analysis of laser micro-structured nickel metal electrodes for application as a cathode material in micro-batteries based on the nickel oxyhydroxide chemistry. Using ultra-short pulse length lasers (picoseconds to femtoseconds); surface micro-structures in the form of ripples are rapidly generated at the surface of nickel metal cathodes. These ripple micro-structures, with a periodic spacing approximately equal to the wavelength of laser radiation used, are more commonly referred to as laser-induced periodic plasmonic structures (LIPPS). The electrochemical activity of the LIPPS nickel metal cathodes is investigated in aqueous KOH using cyclic voltammetry. Across a wide range of scan rates, the results of the voltammetry show that the formation of LIPPS yields a considerable enhancement in the electrochemical activity of the nickel surface. The observed enhancement is attributed to both the greater surface area of the rippled surface relative to a planar nickel surface and a thicker NiOx layer generated by the laser process.

Honeycomb-structured porous poly(3,4-ethylenedioxythiophene) composite layers on a gold electrode

Three microstructured electrodes modified with poly(3,4-ethylenedioxythiophene) (PEDOT) were obtained. One electrode was modified with PEDOT doped with poly(4-lithium styrenesulfonic acid) (PSSLi), the second one with a PEDOT+polyacrylic acid composite doped with PSSLi, and the third one with a PEDOT+anthranilic acid composite doped with poly(4-styrenesulfonic acid). The three electrodes were prepared using templates of polystyrene latex spheres (PS). The templates were deposited on the electrode using our dip-coating-like technique that we developed by optimizing key parameters, such as PS and sodium dodecyl sulfate concentration, angle of inclination, and decantation rate. The structure of the templates was verified by optical microscopy. A conducting polymer layer was obtained by electropolymerization from appropriate monomer solutions. In the final stage, the template was dissolved in toluene and the morphology of the resulting honeycomb-structure was examined by atomic force microscopy and scanning electron microscopy methods. The electrochemical properties of the electrodes were tested by cyclic voltammetry and electrochemical impedance spectroscopy.

Micro Blood Pressure Energy Harvester for Intracardiac Pacemaker

This paper presents the design, fabrication, and tests of a microspiral-shaped piezoelectric energy harvester and its associated microfabricated packaging that collects energy from ordinary blood pressure variations in the cardiac environment. This device could become a life-lasting, miniaturized energy source for active implantable medical devices such as leadless pacemakers. We present the concept and tested prototypes of 10 μm thin and ultra-flexible electrodeposited microbellows (6mm diameter, 21mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> volume) as a new type of implant packaging. It enables direct blood pressure harvesting and permits a high efficiency of energy transfer to a transducer operating in quasi-static mode and hence adaptable and unaffected by frequent heartbeat frequency changes. Spiral-shaped piezoelectric transducers are introduced for their flexibility and large incoming mechanical energy. Non-trivial optimal electrodes placement and best spiral design parameters are studied and discussed. Three types of spiral prototypes (11mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> volume each) with doubled-sided microstructured electrode patterns are presented and characterized. A power of 3 μJ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /heartbeat and a transduction efficiency of 5.7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> have been obtained for the best designs at 1.5Hz and we predict that twice as much could be obtained using similar design process and material. Through implementing smart adapted electronic circuits, a potential additional tenfold increase in power output could be achieved, which would be sufficient to power a leadless pacemaker.

Silicon Microwire Arrays for Solar Energy-Conversion Applications

Highly structured silicon microwire (Si MW) arrays have been synthesized and characterized as absorbers for solar energy-conversion systems. These materials are of great interest for applications in solar energy conversion, including solar electricity and solar fuels production, due to their unique materials properties, form factors, ease of fabrication, and device-processing attributes. The Si MW array geometry allows for efficient collection of photogenerated carriers from impure materials that have short minority-carrier diffusion lengths while simultaneously allowing for high optical absorption and high external quantum yields for charge-carrier collection. In addition, Si MW arrays exhibit unique mesoscale optical behavior and can be removed from the growth substrate to provide flexible, processable arrays of Si microwires ordered in a variety of organic polymers and ionomers. The unique photon-management properties of Si MW arrays, combined with their high internal surface area and controlled morphology for catalyst placement and support, allow for the use of earth-abundant electrocatalysts to produce an integrated, functional photoelectrode. These materials therefore also provide an opportunity to explore the 3-dimensional photoelectrochemical behavior of fuel-forming microstructured electrodes.

Liquid silicone rubber (LSR)-based dry bioelectrodes: The effect of surface micropillar structuring and silver coating on contact impedance

Bioelectrode–skin contact impedances need to be minimized to enable high quality recordings of biopotentials. Low contact impedances can be achieved with large, effective bioelectrode–skin contact areas. In this study, novel dry microstructured electrodes based on electrically conductive liquid silicone rubber (LSR) were developed and characterized with electrical impedance spectroscopy (EIS) measurements. Two different micropillar structures with inter-pillar distances of 20μm and 100μm, respectively, were compared with smooth LSR electrodes, as such or coated with silver (Ag). A gelatin gel based skin model was used in EIS measurements to overcome the problems associated with real skin measurements. Both microstructurings were found to significantly decrease the contact impedance modulus. In addition, the Ag coating caused highly significant (p<0.01) decrease in impedance modulus for each surface topography, e.g. for smooth electrodes the impedance drop was roughly from 140±30kΩ to 50±10kΩ at 1Hz. The Ag coating combined with microstructuring expectedly revealed the most superior electrical characteristics as the contact impedance declined even as low as 10±2kΩ at 1Hz. Instead, no statistically significant differences in impedance values were detected between the two microstructurings in the uncoated or Ag-coated electrodes. However, more sparse microstructuring (100) seemed to offer lower variation, i.e. more reproducible results. In conclusion, present microstructured electrodes that do not pierce any layer of skin but improve the contact to skin might be a good alternative to conventional wet electrodes.

Structure and photoelectrochemical properties of silicon microstructures arrays

Two silicon microstructrues of silicon nanowires (SiNWs) and silicon microchannel plates (Si MCP) have been successfully fabricated combined by standard microelectronics technology and electrochemical method. The performances have been investigated for dye-sensitized solar cells (DSSCs) by applying silicon nanowires (SiNWs) and silicon microchannel plates (Si MCP) to the counter electrode, respectively. And the electrocatalytic activities of Si MCP and SiNWs electrodes for triiodide reduction were studied using electrochemical impedance spectroscopy. The two microstructure electrodes consisting of a large number of channels with high surface to volume ratio exhibits a highly interconnected network structure with good catalytic activity. A high photovolatic conversion efficiency of over 7.01% and 7.86% were recorded for DSSCs based on the Si MCP and SiNWs counter electrodes, which is comparatable to the cell based on conventional Pt counter electrode at the same condition. It could be expected that this low cost SiNWs and Si MCP and compatibility with microelectronic technology would make the silicon-based monolithic DSSC available in practical application.

Model Ge microstructures as anodes for Li-ion batteries

We examine the properties of microstructured Ge electrodes for Li-ion battery applications. Model-microfabricated single-crystalline Ge electrode structures are used to investigate the effects of Cu coating and partial discharging on cycle life. Results show that the Ge microstructures insert Li more isotropically than do comparable ones comprised of Si. A model Ge microbar electrode with a Cu coating is capable of 95 % coulombic efficiency after 40 cycles when the amount of charge is limited. The microstructured Ge electrode is found to exhibit poor performance at higher delithiation rates (above C/5) relative to microstructured Si electrodes. These results provide an understanding of the effects of electrochemical processes on model-microstructured Ge electrodes which may ultimately aid in the development of advanced anodes for Li-ion batteries.

Impedance-based cell monitoring: barrier properties and beyond

In multicellular organisms epithelial and endothelial cells form selective permeable interfaces between tissue compartments of different chemical compositions. Tight junctions which connect adjacent cells, control the passage of molecules across the barrier and, in addition, facilitate active transport processes. The cellular barriers are not static but can be deliberately modulated by exposure to specific external stimuli. In vitro models representing the essential absorption barriers of the body are nowadays available, thus allowing investigation of the parameters that control permeability as well as transport processes across those barriers. Independent of the origin of the barrier forming cells, techniques are needed to quantify their barrier integrity. One simple assay is to measure the permeability for given hydrophilic substrates possessing different molecular weights like sucrose or dextrans. However, this technique is time-consuming and labor-intensive. Moreover, radioactive or fluorescently-labeled substrates are needed to allow easy analytical detection. Finally, if transport processes are investigated, the standard permeant may interfere with the transport process under investigation or might even alter the barrier integrity by itself. Thus, independent, non-invasive techniques are needed to quantify the barrier integrity continuously during the experiment. Such techniques are available and are mainly based on the measurement of the transendothelial or transepithelial electrical resistance (TEER) of barrier forming cells grown on porous membranes. Simple devices using two sets of electrodes (so-called Voltohmeters) are widely used. In addition, an easy-to-use physical technique called impedance spectroscopy allows the continuous analysis of both the TEER and the electrical capacitance giving additional information about the barrier properties of cells grown on permeable membranes. This technique is useful as a quality control for barrier forming cells. Another impedance-based approach requires cells to be grown directly on solid, micro-structured electrodes. Here, we will discuss the physical background of the different techniques; advantages, disadvantages, and applications will be scrutinized. The aim is to give the reader a comprehensive understanding concerning the range and limits of the application, mainly focusing on endothelial cells.

Poregenic - Patch on Chip System for Adherent Cellular Networks

Automated patch-clamp setups are applied to investigate dose response relationships and target kinetics in the development of new pharmaceutical agents. Currently, automated systems are limited to investigations of suspended single cells. We pursue the development of assays for detecting the membrane properties in adherent networks because the majority of cells in humans grow adherently. In a first step, we developed PoreGenic®, a novel patch-clamp system for cells growing on a sensor chip with micro-structured needle electrodes arranged in an 8×8 multi-electrode array with a pitch of 100 μm.

Preparation and Characterization of Electrodeposited ZnO on Microstructured Electrode Arrays

Interdigitated microstructured electrode arrays of gold or silver bands were used as substrates for the electrodeposition of crystalline ZnO thin films under pulsed galvanostatic conditions from aqueous Zn(NO3)2 solutions. For current densities below the limiting current density, homogenous films of ZnO were obtained as proven by scanning electron and confocal laser microscopy. For current densities greater than those limited by the diffusion of Zn2+ and NO3−, strongly dendritic structures were formed. Film growth was analyzed based on the duplex diffusion layer model. The influence of convective diffusion was directly observed when only one set of electrode bands was polarized during deposition. By use of an underlying gate electrode in the substrate, field-effect measurements were performed to electrically characterize the samples.

A 1.76 V hybrid Zn-O 2 biofuel cell with a fungal laccase-carbon cloth biocathode

A hybrid biofuel cell has been constructed based on the Zn anode and O 2 biocathode, exploiting fungal Cerrena maxima and Choriolus hirsutus laccases cross-linked onto graphite and microstructured graphitized carbon cloth (GCC) electrodes. Immobilized at the graphite electrodes, laccases exhibited a high similarity in the reaction of direct (in the absence of any mediators) bioelectrocatalytic reduction of O 2 starting from 0.7 V vs. Ag/AgCl, pH 5, which was consistent with a 94% structural homology of the laccases. The efficiency of the bioelectrocatalytic reaction was enhanced by immobilizing laccases on the high-surface area GCC, due to the increased surface concentration of the laccase molecules properly orientated for the direct electron transfer reaction within the micro-structured electrode. The hybrid biofuel cell, based on the battery-type Zn anode and oxygen laccase/GCC biocathode yielded the open-circuit voltage V oc of 1.76 V and the short-circuit current density j sc of 4 mA cm −2 in quiescent aerated solutions. A maximum power density of the cell was 0.44 mW cm −2 at the cell voltage of 0.5 V, pH 5. The hybrid biofuel cell exploiting cross-linked stabilized laccases at GCC was able to power a 1.5 V domestic device for 38 days.

Flexible Three-Dimensional Electrochemical Glucose Sensor with Improved Sensitivity Realized in Hybrid Polymer Microelectromechanical Systems Technique

Continuous glucose monitoring for patients with diabetes is of paramount importance to avoid severe health conditions resulting from hypoglycemia or hyperglycemia. Most available methods require an invasive setup and a health care professional. Handheld devices available on the market also require finger pricking for every measurement and do not provide continuous monitoring. Hence, continuous glucose monitoring from human tears using a glucose sensor embedded in a contact lens has been considered as a suitable option. However, the glucose concentration in human tears is very low in comparison with the blood glucose level (1/10-1/40 concentration). We propose a sensor that solves the sensitivity problem in a new way, is flexible, and is constructed onto the oxygen permeable contact lens material. To achieve such sensitivity while maintaining a small sensor footprint suitable for placement in a contact lens, we increased the active electrode area by using three-dimensional (3-D) electrode micropatterning. Fully flexible 3-D electrodes were realized utilizing ordered arrays of pillars with different shapes and heights. We successfully fabricated square and cylindrical pillars with different height (50, 100, and 200 μm) and uniform metal coverage to realize sensor electrodes. The increased surface area produces high amperometric current that increases sensor sensitivity up to 300% using 200 μm tall square pillars. The sensitivity improvement closely follows the improvement in the surface area of the electrode. The proposed flexible glucose sensors with 3-D microstructure electrodes are more sensitive to lower glucose concentrations and generate higher current signal than conventional glucose sensors.

In Situ, Through-Plane Measurements of Ionic Potential in a PEMFC Catalyst Layer

A novel apparatus for measuring in situ, through-plane, ionic potential distribution within the cathode catalyst layer of a polymer electrolyte membrane (PEM) fuel cell is presented here. This new diagnostic method makes use of a micro-structured electrode scaffold (MES), which is a stack of alternating insulating and sensing layers that surround a 100 µm diameter cylinder of catalyst layer material. Here we present measurements of ionic potential at four points through the thickness of a PEM fuel cell cathode. These preliminary results show significant variations of the ionic potential within the electrode at high currents. In addition, the local ionic potential provides an accurate measure of the local IR-free potential in the catalyst layer. Possible applications of the ionic potential data gathered from the MES include investigating mass and charge transport limitations, spatially characterizing electrode kinetics, and validating porous electrode models.

In Situ Measurement of Oxygen Partial Pressure in a Cathode Catalyst Layer

A micro-structured electrode scaffold (MES) was developed for performing in-situ measurements of through-plane oxygen partial pressure (OPP) distributions in the cathode of a polymer electrolyte membrane fuel cell (PEMFC). Alternating layers of insulating material and platinum are stacked and bonded, and surround a 100 micron diameter hole filled with catalyst layer material. The platinum layers serve as ultra-microelectrodes, allowing the measurement of local OPP at discrete intervals through the catalyst layer thickness. Following an investigation of ultra-microelectrode sensitivity and repeatability, pulsed amperometric detection was selected over potentiostatic operation as the most effective method for performing OPP measurements. Using calibration points at the full air and zero OPPs, the OPP distribution at a fuel cell current density of 450 mA cm-2 was measured.