Micrometer-sized Electrodes Research Articles

Optimizing Ni–Cr patterned boron-doped diamond band electrodes: Doping effects on electrochemical efficiency and posaconazole sensing performance

There is growing interest in developing diamond electrodes with defined geometries such as, for example, micrometer-sized electrode arrays to acquire signals for electroanalysis. For electroanalytical sensing applications, it is essential to achieve precise conductive patterns on the insulating surface. This work provides a novel approach to boron-doped diamond patterning using nichrome masking for selective seeding on an oxidized silicon substrate. The optimized process involves nichrome deposition, sonication, chemical etching, seeding, and tailored chemical vapor deposition of boron-doped diamond with an intrinsic layer to suppress boron diffusion. Through a systematic investigation, it was determined that isolated boron-doped diamond band electrodes can be efficiently produced on non-conductive silica. Additionally, the influence of boron doping on electrochemical performance was studied, with higher doping enhancing the electrochemical response of band electrodes. To demonstrate sensing capabilities, boron-doped diamond bands were used to detect posaconazole, an antifungal drug, exploiting its electroactive behaviour. A linear correlation between posaconazole concentration and oxidation peak current was observed over 1.43 × 10−8 – 5.71 × 10−6 M with a 1.4 × 10−8 M detection limit. The developed boron-doped diamond microbands could significantly impact the field of electroanalysis, facilitating detection of diverse biologically relevant molecules. Overall, this diamond patterning approach overcomes major challenges towards all-diamond electrochemical sensor chips.

(Invited) Whisker Growth during Adsorbate Suppressed Electrodeposition

Anisotropic electrochemical deposition and whisker growth is shown to be a consequence of operating a bistable active-passive critical system under galvanostatic control. Specifically, whisker growth is examined during galvanostatic Cu electrodeposition from an electrolyte containing suppressor additives. Disruption of the passivating polyether-halide bilayer triggered by metal deposition leads to positive feedback and highly localized deposition. On macroscale electrodes active-passive Turing patterns develop while on micrometer-sized electrodes the bifurcation is frustrated and proceeds as a single active zone reinforced by hemispherical transport fields. Extended electrodeposition leads to symmetry breaking and lateral propagation of a single whisker. An increasing fraction of the applied current supports expansion of the passive sidewall area and eventually results in termination of anisotropic deposition. The dynamic range between passive versus active growth determines the shape and extent of whisker formation. Similar critical behavior may account for reports of whisker growth in certain metal/metal ion battery systems.

Filament Growth and Related Instabilities during Adsorbate Suppressed Electrodeposition

Anisotropic growth of a single filament on a microelectrode is demonstrated by galvanostatic electrodeposition in a bistable passive-active critical system. Specifically, a Cu filament is formed by disruption of a passivating polyether-halide bilayer triggered by metal deposition with positive feedback guiding highly localized deposition. For macroscale electrodes, complex passive-active Turing patterns develop, while for micrometer-sized electrodes, bifurcation is frustrated and a single active zone develops, which is reinforced by hemispherical transport. As deposition proceeds, hemispherical symmetry is broken with lateral propagation of a single filament while an increasing fraction of the applied current supports expansion of the passive sidewall area that eventually leads to termination of anisotropic growth. Different polyether suppressors alter the dynamic range between passive and active growth that determines the shape and extent of filament formation. The impact of electrode area, geometry, and applied current on morphological evolution was also briefly examined. The results highlight the utility of appropriately scaled microelectrodes in the study of growth instabilities during breakdown of additive suppressed layers in critical electrodeposition systems.

Microbatteries with twin-Swiss-rolls redefine performance limits in the sub-square millimeter range.

To maintain the downscaling of microelectronic devices with footprints less than one square millimeter, next-generation microbatteries should occupy the same area and deliver adequate energy for running a new generation of multi-functional microautonomous systems. However, the current microbattery technology fails in accomplishing this task because the micrometer-sized electrodes are not compatible with on-chip integration protocols and technologies. To tackle this critical challenge, an on-chip Swiss-roll microelectrode architecture is employed that exploits the self-assembly of thin films into ultra-compact device architectures. A twin-Swiss-roll microelectrode on a chip occupies a footprint of 0.045 mm2 and delivers an energy density up to 458 μW h cm-2. After packaging, the footprint of a full cell increases to 0.11 mm2 with a high energy density of 181 μW h cm-2. The volumetric energy density excluding the chip thickness is 16.3 mW h cm-3. These results open opportunities for deploying microbatteries as energy and power sources to drive smart dust microelectronics and microautonomous systems.

A flexible protruding microelectrode array for neural interfacing in bioelectronic medicine

Recording neural signals from delicate autonomic nerves is a challenging task that requires the development of a low-invasive neural interface with highly selective, micrometer-sized electrodes. This paper reports on the development of a three-dimensional (3D) protruding thin-film microelectrode array (MEA), which is intended to be used for recording low-amplitude neural signals from pelvic nervous structures by penetrating the nerves transversely to reduce the distance to the axons. Cylindrical gold pillars (Ø 20 or 50 µm, ~60 µm height) were fabricated on a micromachined polyimide substrate in an electroplating process. Their sidewalls were insulated with parylene C, and their tips were optionally modified by wet etching and/or the application of a titanium nitride (TiN) coating. The microelectrodes modified by these combined techniques exhibited low impedances (~7 kΩ at 1 kHz for Ø 50 µm microelectrode with the exposed surface area of ~5000 µm²) and low intrinsic noise levels. Their functionalities were evaluated in an ex vivo pilot study with mouse retinae, in which spontaneous neuronal spikes were recorded with amplitudes of up to 66 µV. This novel process strategy for fabricating flexible, 3D neural interfaces with low-impedance microelectrodes has the potential to selectively record neural signals from not only delicate structures such as retinal cells but also autonomic nerves with improved signal quality to study neural circuits and develop stimulation strategies in bioelectronic medicine, e.g., for the control of vital digestive functions.

Electrolithic Memory: A New Device for Ultrahigh-Density Data Storage

We propose a storage memory device that enables bit densities of >1 Tbit/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> based on the electro- deposition and electrodissolution of multilayered metal stacks in deep nanometer-sized wells. This device addresses the challenge of bit density scaling slowdown expected for 3-D NAND flash beyond 2030. We describe in detail the operating principles and discuss the response time, bandwidth, retention, and cycling endurance requirements for the device to be viable. As a proof-of-principle, we provide a first demonstration of the write/read (W/R) mechanism on millimeter- and micrometer-sized electrodes and show the device’s potential for reaching very high bit densities. To evaluate how the response time scales for the envisioned nanometer-sized electrodes, we derive simple analytical expressions based on finite element simulations that relate the well depth, radius, and electrolyte composition to the deposition/dissolution rate.

Probing the oscillating Belousov-Zhabotinskii reaction with micrometer-sized electrodes: the effect of C, Pt, and Au

Probing the oscillating Belousov-Zhabotinskii reaction with micrometer-sized electrodes: the effect of C, Pt, and Au

Converting Any Faradaic Current Generated at an Electrode under Potentiostatic Control into a Remote Fluorescence Signal.

We describe the development of an original faradaic current-to-fluorescence conversion scheme. The proposed instrumental strategy consists of coupling the electrochemical reaction of any species at an electrode under potentiostatic control with the fluorescence emission of a species produced at the counter electrode. In order to experimentally validate this scheme, the fluorogenic species resazurin is chosen as a fluorescent reporter molecule, and its complex reduction mechanism is first studied in unprecedented detail. This kinetic study is carried out by recording simultaneous cyclic voltammograms and voltfluorograms at the same electrode. Numerical simulations are used to account for the experimental current and fluorescence signals, to analyze their degree of correlation, and to decipher their relation to resazurin reduction kinetics. It is then shown that, provided that the reduction of resazurin takes place at a micrometer-sized electrode, the fluorescence emission perfectly tracks the faradaic current. By implementing this ideal configuration at the counter electrode of a potentiostatic setup, it is finally demonstrated that the oxidation reaction of a nonfluorescent species at the working electrode can be quantitatively transduced into simultaneous emission of fluorescence.

Correction to "Direct Electrochemical Measurements of Reactive Oxygen and Nitrogen Species in Nontransformed and Metastatic Human Breast Cells".

The production of reactive oxygen and nitrogen species (ROS and RNS) in human cells is implicated in various diseases, including cancer. Micrometer-sized electrodes coated with Pt black and platinized Pt nanoelectrodes have previously been used for the detection of primary ROS and RNS in biological systems. In this Article, we report the development of platinized carbon nanoelectrodes with well-characterized geometry and use them as scanning electrochemical microscopy (SECM) tips to measure ROS and RNS inside noncancerous and metastatic human breast cells. By performing time-dependent quantitative amperometric measurements at different potentials, the relative concentrations of four key ROS/RNS in the cell cytoplasm and their dynamics were determined and used to elucidate the chemical origins and production rates of ROS/RNS in nontransformed and metastatic human breast cells.

Direct Electrochemical Measurements of Reactive Oxygen and Nitrogen Species in Nontransformed and Metastatic Human Breast Cells.

The production of reactive oxygen and nitrogen species (ROS and RNS) in human cells is implicated in various diseases, including cancer. Micrometer-sized electrodes coated with Pt black and platinized Pt nanoelectrodes have previously been used for the detection of primary ROS and RNS in biological systems. In this Article, we report the development of platinized carbon nanoelectrodes with well-characterized geometry and use them as scanning electrochemical microscopy (SECM) tips to measure ROS and RNS inside noncancerous and metastatic human breast cells. By performing time-dependent quantitative amperometric measurements at different potentials, the relative concentrations of four key ROS/RNS in the cell cytoplasm and their dynamics were determined and used to elucidate the chemical origins and production rates of ROS/RNS in nontransformed and metastatic human breast cells.

Facile fabrication of carbon ultramicro- to nanoelectrode arrays with tunable voltammetric response.

The voltammetric response for nano- to micrometer-sized electrode arrays are represented by two major regimes: a sigmoidal shaped i-v response for arrays acting as individual electrodes in parallel and peak-shaped i-v response for arrays acting as an ensemble in concert. Here, we present a facile and versatile technique to fabricate ultramicro- to nanoelectrode arrays using atomic layer deposition of insulating Al2O3 on conductive carbon films masked by 1.54, 11, or 90-μm-diameter polystyrene spheres (PSS). The ratio between the interelectrode distance and the electrode radii of the electrode arrays is a predictable function of the PSS radius used in fabrication, resulting in electrode arrays with a tunable voltammetric response. Arrays are characterized utilizing cyclic voltammetry and electrochemical impedance spectroscopy, which provides the critical scan rate, νcrit, the scan rate at which the radial diffusion layers of the individual electrodes overlap and appear as a single linear diffusion layer. Thus, below ν(crit), the electrode has a peak-shaped i-v response associated with semi-infinite linear diffusion, whereas above this critical scan rate, the i-v response is sigmoidal as a result of hemispherical radial diffusion. Results indicate that the critical scan rates are 6.6, 1.0, and 0.01 V/s for the 1.54, 11, and 90 μm PSS prepared electrode arrays, respectively.

A platform for in-situ multi-probe electronic measurements and modification of nanodevices inside a transmission electron microscope

We developed a new platform that enables in-situ four-probe electronic measurements, in-situ three-probe field-effect measurements, nanomanipulation, and in-situ modification of nanodevices inside a transmission electron microscope (TEM). The platform includes a specially designed chip-holder and a silicon (Si) chip with suspended metal electrodes. The chip-holder can hold one Si chip with a size up to 3 mm × 3 mm and provides four electrical connections that can be connected to the micrometer-sized electrodes on the Si chip by wire-bonding. The other side of the electrical connections on the chip-holder is connected to the electronic instruments outside the TEM through a commercial Nanofactory SPM-TEM holder. The Si chip with suspended metal electrodes on one of its edges was fabricated by lithography and wet etching. Carbon nanotubes (CNTs), InAs nanowires, and tungsten disulfide nanowires were placed to stride over and connect to the suspended electrodes on the Si chip by nanomanipulations inside a scanning electron microscope (SEM). By using the platform, I-V curves of an individual single-walled CNT connecting to four electrodes were in-situ measured between any two of the four suspended electrodes, and a high-resolution TEM image of the same CNT was obtained. Furthermore, four-terminal I-V measurement on an InAs nanowire was achieved on this platform, and with a movable probe used as a gate electrode, field-effect measurement on the same InAs nanowire device was accomplished in SEM. In addition, by using the movable probe on the SPM-TEM holder, we could further in-situ modify nanomaterial and nanodevices. The present work demonstrates a method that allows a direct correlation between the atomic-level structure and the electronic property of nanomaterials or nanodevices whose structure can be further modified in-situ.

Nanoelectrodes for determination of reactive oxygen and nitrogen species inside murine macrophages.

Reactive oxygen and nitrogen species (ROS and RNS) produced by macrophages are essential for protecting a human body against bacteria and viruses. Micrometer-sized electrodes coated with Pt black have previously been used for selective and sensitive detection of ROS and RNS in biological systems. To determine ROS and RNS inside macrophages, one needs smaller (i.e., nanometer-sized) sensors. In this article, the methodologies have been extended to the fabrication and characterization of Pt/Pt black nanoelectrodes. Electrodes with the metal surface flush with glass insulator, most suitable for quantitative voltammetric experiments, were fabricated by electrodeposition of Pt black inside an etched nanocavity under the atomic force microscope control. Despite a nanometer-scale radius, the true surface area of Pt electrodes was sufficiently large to yield stable and reproducible responses to ROS and RNS in vitro. The prepared nanoprobes were used to penetrate cells and detect ROS and RNS inside macrophages. Weak and very short leaks of ROS/RNS from the vacuoles into the cytoplasm were detected, which a macrophage is equipped to clean within a couple of seconds, while higher intensity oxidative bursts due to the emptying of vacuoles outside persist on the time scale of tens of seconds.

Open-cell recording of action potentials using active electrode arrays

The investigation of complex communication in cellular networks requires superior measurement tools than those available to date. Electrode arrays integrated onto silicon electronics are increasingly used to measure the electrical activity of cells in an automated and highly parallelized fashion, but they are restricted to recording extracellular potentials. Here, we report on an array of TiN electrodes built using standard silicon electronics for intracellular action potential recording. Intracellular access, possible at each of the 16 384 electrodes on the chip, was accomplished by local membrane electroporation using electrical stimulation with subcellular, micrometer-sized electrodes. Access to the cell interior was transient and could be tuned in duration by adapting the electroporation protocol. Intracellular sensing was found to be minimally invasive in the short and long-term, allowing consecutive intracellular recordings from the same cell over the course of days. Finally, we applied this method to investigate the effect of an ion channel blocker on cardiac electrical activity. This technique opens the door to massively parallel, long-term intracellular recording for fundamental electrophysiology and drug screening.

A simple approach for fabrication of dual-disk electrodes with a nanometer-radius electrode and a micrometer-radius electrode

We developed a new simple approach to fabricate dual-disk electrodes with a nanometer-radius electrode and a micrometer-radius electrode. First, nanometer-sized electrodes and micrometer-sized electrodes were constructed using 10-μm-radius metal wires, respectively. To fabricate the nanometer-sized electrode, after the apex of the 10-μm-radius metal wire was electrochemically etched to an ultrafine point with a nanometer-radius, the metal wire was electrochemically coated with a phenol–allyphenol copolymer film. The micrometer-sized electrode was fabricated by directly electrochemical coating the metal wire with an extremely thin phenol–allyphenol copolymer film. Then, the nanometer-radius electrode (the first electrode) and the 10-μm-radius electrode (the second electrode) were inserted into two sides of a thick-septum borosilicate theta ( θ) tubing, respectively. The second electrode protruded from the top of the θ tubing. The top of the θ tubing was sealed with insulating ethyl α-cyanoacrylate. The top of the θ tubing with both electrodes was ground flat and polished successively with fine sandpaper and aluminum oxide powder until the tip of the first electrode was exposed. Since the second electrode protruded from the top of the θ tubing, its 10-μm-radius tip was naturally formed during polishing. The dual-disk electrodes were characterized by scanning electron microscopy and cyclic voltammetry. The success rate for fabrication of the dual-disk electrodes is ∼80% due to double insurance from two coating layers of different polymers.

High Frequency Faradaic Rectification Voltammetry at Microelectrodes

An experimental setup for carrying out faradaic rectification measurements at micrometer-sized electrodes under potential control is described. A new method of data analysis is proposed that allows the determination of the standard rate constant and the electron-transfer coefficient of a fast charge transfer process without knowing the impedance of the microelectrode. This method is based on the frequency dependence of the shape of the faradaic rectification voltammograms (i.e., the average width of the peaks and the ratio of the peak heights) rather than on the magnitude of the faradaic rectification signal. The method was tested in the determination of heterogeneous electron transfer kinetics of Fe(CN)6(3-/4-) and Ru(NH3)6(2+/3+) in aqueous solutions on a platinum microelectrode (12.5 microm in radius) and ferrocene/ferrocinum redox couple in a dimethylformamide solution on a gold microelectrode (12.5 microm in radius).

Hydrodynamics and Mass Transport in Wall Tube and Microjet Electrodes. Simulation and Experiment for Micrometer-Scale Electrodes

Mass transport to micrometer-sized electrodes in a microjet (wall-tube) electrode configuration is examined experimentally and through finite element modeling. Electrochemical imaging experiments reveal that local mass transport is highly sensitive to the lateral position of the nozzle with respect to the electrode. When these two components are arranged coaxially, there is a pronounced minimum in the mass transfer rate to the electrode, as determined from transport-limited current measurements. Small lateral displacements of the nozzle from the coaxial position lead first to an increase in mass transport, with the current reaching a maximum at a displacement of around one nozzle radius (50 μm). For larger lateral displacements of the nozzle from the coaxial position, the limiting current gradually decreases with increasing distance. The implications of these observations for practical applications of the microjet electrode are considered. Voltammetric measurements on the oxidation of IrCl63- in aqueous solution, with the electrode and nozzle coaxial are shown to be in good agreement with simulation of mass transport. Increasing the solution viscosity dramatically decreases mass transport to the electrode, with the reduction in the diffusion coefficient of the redox species as the major factor.

EVEN FLOW BUILDS MICROSTRUCTURES

Gentle motions of reactive fluids flowing through capillaries form the basis of a new microfahrication procedure that offers great simplicity compared with other methods. The new method, which may be applied to materials that aren't amenable to other fabrication techniques, has been used with high precision to build micrometer-sized electrode systems and other devices [ Science , 285 , 83 (1999)]. The procedure was developed by Harvard University chemistry professor George M. Whitesides and postdoctoral associates Paul J. A. Kenis and Rustem F. Ismagilov. By selecting conditions that promote a mild and nonturbulent type of mass transport known as laminar flow, the Harvard researchers carry out chemical reactions strictly at the interface between streams of solutions flowing side-by-side through minuscule channels or at the interface of tiny reagent streams and capillary walls. These reactions leave in their wake lines of metal atoms or other products that can serve as microelectronic devices. It's a real...

High-Frequency Impedance Spectroscopy of Platinum Ultramicroelectrodes in Flowing Solutions

A method for studying impedance spectroscopy of micrometer-sized electrodes in the frequency range from 5 kHz to 5 MHz has been developed and tested. Details of the electronic circuit and the data processing method are provided. Since the method involves high-speed data acquisition and fast Fourier transformation, the impedance data can be obtained within a 5-ms time window. This enables measurement of changes in the electrode impedance caused by rapid changes in the solution composition. In particular, the method is well suited to studying the performance of electrochemical microdetectors in flowing solutions. The performance of the method was tested in a brief study of the competitive adsorption of hydrogen and methionine on a Pt ultramicroelectrode. It has been shown that proper electrochemical conditioning can prevent any long-term changes in the properties of the electrode caused by its exposure to common organic or inorganic substances. Hence, it provides means for making an ultramicroelectrode with...

Molecular dielectrophoresis of biopolymers

Dielectrophoresis (DEP) has found wide applications in manipulations of micrometer-sized particles such as biological cells. However, it has been considered less effective for nanometer-sized particles such as biological macromolecules where DEP effects may be overwhelmed by Brownian motion. Here, the authors use the fluid integrated circuit (FIC) concept to fabricate micrometer-sized electrodes, with which a very high-intensity, steady-state, high-frequency field, over 1/spl times/10/sup 6/ V/m at 1 kHz to 10 MHz, is created. The observation of molecular DEP using avidin (68 kD) and other biopolymers is made, and it is found that DEP occurs at the field strength of 0.4-1.0/spl times/10/sup 6/ V/m, which is substantially lower than DEP theory predicts. As applications of molecular DEP, a novel molecular patterning method and "dielectrophoretic chromatography" are proposed. In the latter, biopolymer solution is moved through a high-intensity field region created in a FIC, and the polymer is analyzed and/or separated by the difference in the DEP attraction.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>