Copper Microelectrodes Research Articles

Gold-dispersed hierarchical flower-like copper oxide microelectrodes for the sensitive detection of glucose and lactic acid in human serum and urine.

Herein, we report self-supported gold-dispersed copper oxide microflowers (Au@CuO MFs) on copper microelectrodes (CMEs) as a sensitive platform for the sensing of glucose and lactic acid in human serum and urine samples. The direct growth of a new class of gold-dispersed copper oxide microflowers on Cu microelectrodes involves growing flower-like passivated copper microelectrodes in nitric acid followed by the galvanic replacement of copper atoms with gold atoms without employing any surfactant or polymer or without the use of any catalysts or complicated procedures. The as-fabricated gold-dispersed copper oxide microflower microelectrodes (Au@CuO MFs|CME) were employed as potential signal transducers for the sensitive detection of glucose and lactic acid in practical samples. The present Au@CuO MFs|CME microsensor demonstrates an extensive linear detection range from 5.0 μM to 0.5 mM for glucose with a low limit of detection (LOD) of ∼1.41 μM and a sensitivity of ∼4.14 mA μM-1 cm-2, and from 100 nM to 88.0 μM for lactic acid with a LOD of ∼27.0 nM and a sensitivity of ∼6.19 mA μM-1 cm-2. The present multi-functional nanoarchitectured Au@CuO MFs|CME microsensor is anticipated to offer unique surface characteristics and synergistic effects, and can be exploited in various electrochemical fields.

Segmented manufacturing of micro-electrode based on EDM and its performance evaluation

Micro-EDM is widely used in micro-hole and 3D micro-structures. However, the application of Micro-EDM is limited due to the scarcity of micro-electrodes. Therefore, the preparation of micro-electrodes has been one of the difficult and hot issues in the field of EDM. In this study, EDM is used to make micro-electrodes. In order to ensure the high dimensional accuracy of the micro-electrode, a parametric study is conducted by replicating a copper electrode with a diameter of 1mm to a steel block by the method of segmented manufacturing. The relationships between the drilled cavities on the block and the features on the micro-electrode are established. The effects of machining parameters (current, pulse width and pulse interval) on the response variables (electrode bottom side length, electrode length, material removal rate, surface roughness and side length deviation rate) are investigated. Current and pulse width are found more dominant as compared to other selected process parameters. Using optimized parameters from the parametric study, a copper micro-electrode of 46µm bottom side length and 1773µm length is fabricated. A micro-channel with a length of 1200µm, a width of 85µm and a depth of 35µm was processed on the copper sheet.

Predicting Vodka Adulteration: A Combination of Electronic Tongue and Artificial Neural Networks

An artificial neural network was used to build models caple of predicting and quantifying vodka adulteration with methanol and/or tap water. A voltammetric electronic tongue based on gold and copper microelectrodes was used, and 310 analyses were performed. Vodkas were adulterated with tap water (5 to 50% (v/v)), methanol (1 to 13% (v/v)), and with a fixed addition of 5% methanol and tap water varying from 5 to 50% (v/v). The classification model showed 99.5% precision, and it correctly predicted the type of adulterant in all samples. Regarding the regression model, the root mean squared error was 3.464% and 0.535% for the water and methanol addition, respectively, and the prediction of the adulterant content presented an R2 0.9511 for methanol and 0.9831 for water adulteration.

Arrays of Copper Microelectrodes from Disposable Chips: Fabrication and Characterization

A simple, fast, and low-cost process to fabricate arrays of copper microelectrodes (CuMEs) based on disposable electronic microchips is described. Arrays with 8 to 20 CuMEs were characterized by energy-dispersive X-ray spectroscopy and cyclic voltammetry techniques. The closest interelectrode distance in the arrays is 358 ± 22 μm, and the minor radius ranged from 10.6 to 13.5 μm. The microchips with CuMEs were sealed in epoxy resin to fabricate the rod and flat-shaped platforms, allowing the CuMEs to be addressed separately. Glucose, hydrazine, and nitrate were used as analyte models for voltammetric and amperometric detection at CuMEs arrays, showing excellent performance in batch and flow-through cells. Glucose measurements carried out with flow injection analysis system with amperometric detection at an array of 20 CuMEs showed a wide linear range (0.020-4.0 mmol L-1), high sensitivity (734.1 μA L mmol-1 cm-2), and a limit of detection of 1.7 μmol L-1.

Study of biochip integrated with microelectrodes modified by poly-dopamine-co-chitosan composite gel for separation, enrichment and detection of microbes in the aerosol

As the urgent need for rapid detection of airborne microbes in a specific environment, a biochip which was integrated with the functions of enrichment and detection was designed and developed. It was composed of cover plate, copper microelectrodes modified with poly-dopamine-co-chitosan (PDA-co-CS) composite gel, sealing washer and substrate containing copper sheet electrode. The microbes were enriched due to the good ventilation efficiency and adhesion of the PDA-co-CS composite gel. The enrichment efficiency of microbes was 99.9%. The electrical impedance spectrum (EIS) test system which was composed of the copper electrodes and the copper sheet electrode were used to detect the concentrated microbes and establish the quantitative detection method of single microbe (S. aureus ATCC 6538) and mixed microbes (S. aureus ATCC 6538, E. coli JM109, and Candida albicans). It was shown that the biochip could respond to the aerosol with 1.26 × 103 cfu/m3S. aureus ATCC 6538, which was 25 times as high as the detection limit of natural deposition method. Meanwhile, the Surface-enhanced Raman Spectrum (SERS) of different microbes were detected in-situ with the help of the silver sol. The SERS data of S. aureus, E. coli and Candida albicans had been analyzed to establish recognition model by the principal component analysis (PCA) method and the three microbes were successfully identified. It was demonstrated that the designed biochip could be applied for separation, enrichment and detection of microbes in the aerosol.

The wear of 3D microelectrode in micro electrical discharge machining

Three-dimensional (3D) microelectrodes can be fabricated by laminating multilayer copper microelectrodes. When the 3D microelectrode is used for micro electrical discharge machining (micro-EDM), the 3D microstructure can be obtained with an up-and-down reciprocating motion. The process is simple and the machining efficiency is high. In micro-EDM process, the 3D microelectrode has wear, which affects the shape accuracy and dimensional accuracy of the microstructure. To obtain the wear characteristics and predict the wear of the 3D microelectrode, the paper discretized 3D microelectrode into several microelectrodes with square cross-sections. The discretized 3D microelectrodes comprised a number of α-type electrodes, β-type electrodes, and γ-type electrodes. The wear of these microelectrodes was studied by numerous experiments, and the wear characteristics of individual microelectrodes were integrated to obtain the wear characteristics of the 3D microelectrode. The study found that the wear of these three types of electrodes was linearly related to the machining depth. The fit slope of the α-type electrode was equal to − 0.24071, and it had the most wear. The fit slope of the β-type electrode was equal to − 0.21524, and it had the second-highest wear. The fit slope of the γ-type electrode was equal to − 0.19767, and its wear was the lowest. Finally, a 3D microelectrode with semi-cylindrical features was used for micro-EDM to verify the correctness of the wear characteristics. The experimental results were compared with the theoretical calculation, and the theoretical calculation of the 3D microelectrode wear was basically consistent with the experimental results. The maximum error between the theoretical calculation and the experimental results was 21.85 μm, and the minimum error was 3.16 μm.

An Electrochemically Synthesized Nanoporous Copper Microsensor for Highly Sensitive and Selective Determination of Glyphosate

AbstractA nanoporous copper (NPC) film was electrodeposited on a copper microelectrode, and the generated platform was investigated for electrochemical sensing of glyphosate (Glyp). The as‐deposited NPC film was highly pure and crystalline according to results of energy dispersive spectroscopy and X‐ray diffraction experiments, respectively. Scanning electron microscopy images confirm the NPC films possess a highly porous morphology containing dendrite fractals, and the electrodeposition parameters, particularly potential (Ed) and time (td), exert a remarkable influence on the structure of the films. Such changes in the NPC morphology with Ed and td were also correlated with the electrochemical behavior investigated by cyclic voltammetry. In the presence of Glyp, the anodic oxidation is facilitated because copper ions diffuse easily through the pores of the NPC film and form a complex with the analyte at the electrode interface. On the other hand, as the amount of copper oxides decreases due to the formation of soluble Cu(II) complex with Glyp, less current is obtained during the reverse scan, allowing a relationship between the decrease in the cathodic current and the Glyp concentration to be established. The optimized NPC‐modified Cu microelectrode showed very high sensitivity (14 nA nmol−1 L), low detection limit (4 nmol L−1), excellent reproducibility, and selective response for Glyp. The applicability of the sensor was demonstrated by detecting Glyp in river water samples.

Study on reducing side etching of Copper microelectrode by multi-step etching process

A method for reducing the amount of copper (Cu) electrode side etching at the micro-nano scale by multi-step etching process was proposed. Taking the positive photoresist (PR) BP212 as a masking layer, the Cu electrode was patterned by two etching solutions, which can effectively reduce the side etching. The x-ray diffraction (XRD) test showed that the intermediate product formed on the surface of Cu during the corrosion of FeCl3 solution was cuprous chloride (CuCl). The removal of CuCl by KCl solution instead of FeCl3 solution greatly reduced the residence time of Cu in FeCl3 solution; The effect of different concentrations of FeCl3 solution on reducing the amount of side etching was studied. The result shows that the FeCl3 solution with mass concentration of 0.03 g ml−1 was used for multi-step etching, and the amount of side etching is reduced from 25 μm to 5 μm.

Effects of dissolved gases on partial anodic passivation phenomena at copper microelectrodes immersed in aqueous NaCl

Anodic passivation for copper exposed to aqueous NaCl (model seawater) is rate limited by diffusion of a poorly soluble Cu(I) chloro species. As a result, a protective layer of CuCl forms on copper metal (with approx. 1 μm thickness) that is then put under strain at more positive applied potentials with explosive events causing current spikes and particulate product expulsion. In this report, the mechanism for this explosive film rupture and particle expulsion process is shown to occur (i) in the absence of underlying anodic gas evolution, and (ii) linked to the presence/nature of gaseous solutes. The film rupture event is proposed to be fundamentally dependent on gas bubble nucleation (triggered by the release of interfacial stress) with surface tension effects by dissolved gases affecting the current spike pattern. Oxygen O2, hydrogen H2, and helium He suppress current spikes and behave differently to argon Ar, nitrogen N2, and carbon dioxide CO2, which considerably enhance current spikes. Vacuum-degassing the electrolyte solution results in behaviour very similar to that observed in the presence of helium. The overall corrosion rate for copper microelectrodes is compared and parameters linked to passivation and corrosion processes are discussed.

Copper micro-electrode fabrication using laser printing and laser sintering processes for on-chip antennas on flexible integrated circuits

Recent advances in flexible electronics have highlighted the importance of high throughput, digital additive microfabrication techniques. In this work, we demonstrate the combination of laser printing and laser sintering of a novel copper nanoparticle ink onto flexible substrates in order to produce oxide free conductive copper patterns in ambient atmospheric conditions. The printed patterns exhibit high reproducibility, very low resistivity (about 2x bulk), and negligible oxidation according to Raman spectroscopy. The process has been employed for the fabrication of an on-chip antenna on a flexible substrate for use in combination with a flexible circuit, in applications where a small form factor and simplicity of integration are required alongside ultra-low cost, e.g. consumable tagging.

In situ laser-induced codeposition of copper and different metals for fabrication of microcomposite sensor-active materials

We report one-step in situ laser-induced synthesis of the conductive copper microstructures doped with iron, zinc, nickel, and cobalt with highly developed surface area. It was observed that the presence of chlorides of the aforementioned metals in the solutions used in our experiments increases the deposition rate and the amount of copper in the resulting deposits; it also leads to the deposit miniaturization. The laser deposition from solutions containing cobalt (II) chloride of concentration more than 0.003 M results in fabrication of copper microelectrode with better electrochemical properties than those deposited from solutions containing chlorides of other metals of the same concentration. Moreover, copper microelectrode doped with cobalt has demonstrated good reproducibility and long-run stability as well as sensitivity and selectivity towards determination of hydrogen peroxide (limit of detection-0.2 μM) and d-glucose (limit of detection-2.2 μM). Thus, in this article we have shown the opportunity to manufacture two-phase microcomposite materials with good electrical conductivity and electrochemical characteristics using in situ laser-induced metal deposition technique. These materials might be quite useful in development of new perspective sensors for non-enzymatic detection of such important analytes as hydrogen peroxide and glucose.

USING AN ACTIVATED COPPER MICROELECTRODE FOR VOLTAMMETRIC DETERMINATION OF ALCOHOLS

A method for fabricating a copper microdisk electrode of an original design based on 50 μm diameter wire sealed in borosilicate glass is described. The electrochemical properties of the copper microelectrode were studied by the method of steady-state voltammetry in a 2 M NaOH solution in the potential range from -1.1 to 0.8 V (versus saturated Ag/AgCl-electrode). In order to improve the electrochemical response a method for two-stage electrode activation based on a copper dissolution / redeposition procedure followed by polarization in an alkaline medium is suggested. Morphological and physico-chemical changes on copper surface after activation were examined by atomic force microscopy and X-ray photoelectron spectroscopy. After this procedure, the electrode showed a heterogeneous morphology with coarse texture and high roughness parameters, and a layer of catalytically active Cu(III) species was formed on copper surface. The best results were achieved with an activation time of 60 s and a polarization potential of -0.3 V. The effectiveness of the activation procedure was tested during the chronoamperometric determination of methanol, ethanol and ethylene glycol. Factors affecting the formation of the analytical signal of alcohols were studied, and optimal conditions of amperometric measurements were selected on their basis. Under optimal conditions, the metrological characteristics of the method were determined. The peak current response increases linearly with alcohols concentration over the range 0.01 - 0.45 M (0.04 - 3% v/v). The repeatability of the electrode response was evaluated as 3.8% (n = 10). The activated copper microelectrode was used for the determination of ethanol in pharmaceutical and other products.

Linking the Cu(II/I) potential to the onset of dynamic phenomena at corroding copper microelectrodes immersed in aqueous 0.5 M NaCl

Electrochemical studies have been conducted at copper microelectrodes (125, 50, and 25 μm in diameter) immersed in aqueous 0.5 M NaCl. Cyclic and linear sweep voltammetry were used to explore the corrosion of copper in chloride media. Cyclic voltammetry revealed the reversible Cu(I)/Cu(0) potential at approximately −0.11 V vs. SCE associated with the formation of a dense CuCl blocking layer (confirmed by in situ Raman and fluorescence measurements). Although continuous dissolution of Cu(I) occurs, only an increase in the driving potential into the region of the Cu(II)/Cu(I) potential at approximately +0.14 V vs. SCE started more rapid and stochastic dissolution/corrosion processes. The corrosion process is demonstrated to be linked to two distinct mechanisms based on (A) slow molecular dissolution and (B) fast colloidal dissolution. A polymer of intrinsic microporosity (PIM-EA-TB) is employed to suppress colloidal processes to reveal the underlying molecular processes.

Graphene Encapsulated Copper Microwires as Highly MRI Compatible Neural Electrodes.

Magnetic resonance imaging (MRI) compatible neural electrodes are important for combining high-resolution electrophysiological measurements with more global MRI mapping of brain activity, which is critical for fundamental neuroscience studies, as well as clinical evaluation and monitoring. Copper is a favorable material to use in MRI because it has magnetic susceptibility close to water and tissues. However, the cytotoxicity of copper precludes its direct implantation for neural recording. Here, we overcome this limitation by developing a graphene encapsulated copper (G-Cu) microelectrode. The toxicity of copper is largely eliminated, as evidenced by the in vitro cell tests and in vivo histology studies. Local field potentials and single-unit spikes were recorded from rodent brains with the G-Cu microelectrodes. Notably, the G-Cu microelectrodes show no image artifacts in a 7.0 T MRI scanner, indicating minimal magnetic field distortion in their vicinity. This high MRI compatibility of our G-Cu probes would open up new opportunities for fundamental brain activity studies and clinical applications requiring continuous MRI and electrophysiological recordings.

Ultrasensitive, Label Free, Chemiresistive Nanobiosensor Using Multiwalled Carbon Nanotubes Embedded Electrospun SU-8 Nanofibers.

This paper reports the synthesis and fabrication of aligned electrospun nanofibers derived out of multiwalled carbon nanotubes (MWCNTs) embedded SU-8 photoresist, which are targeted towards ultrasensitive biosensor applications. The ultrasensitivity (detection in the range of fg/mL) and the specificity of these biosensors were achieved by complementing the inherent advantages of MWCNTs such as high surface to volume ratio and excellent electrical and transduction properties with the ease of surface functionalization of SU-8. The electrospinning process was optimized to precisely align nanofibers in between two electrodes of a copper microelectrode array. MWCNTs not only enhance the conductivity of SU-8 nanofibers but also act as transduction elements. In this paper, MWCNTs were embedded way beyond the percolation threshold and the optimum percentage loading of MWCNTs for maximizing the conductivity of nanofibers was figured out experimentally. As a proof of concept, the detection of myoglobin, an important biomarker for on-set of Acute Myocardial Infection (AMI) has been demonstrated by functionalizing the nanofibers with anti-myoglobin antibodies and carrying out detection using a chemiresistive method. This simple and robust device yielded a detection limit of 6 fg/mL.

Characterization of copper microelectrodes, following a homemade lithography, technique, and gold electroless deposition

We report the fabrication and characterization of copper microelectrodes obtained by a homemade lithography technique and after gold electroless deposition. For the fabrication, planes consisting of arrays of electrodes (black in color) with bow tie shape were designed and printed on a transparent paper (Canson ltd.). Using an embroidery frame with a silk fabric, a photographic emulsion was spread on the silk and simultaneously pressing the Canson paper on it. The system was introduced into a closed box and exposed with a UV light. The designed electrode templates prevented direct exposition of the UV light over copper films and indelible ink was spread over it. After the ink was dried, the copper film is immersed into ferric acid to attack the uncovered copper parts (where there is no ink). In this way, we obtained copper electrodes with initial gap separation of ~142μm and subsequently, they followed electroless deposition of gold to make the copper electrodes to contact. For the characterization, electrical measurements were performed. They present ohmic resistance values in the order of 106 Ω produced by surface scattering of the electrons within the gold microwire and enhanced by oxidation of the copper electrodes.

Performance and Limitations of the Conventional Electrode Materials for Erosion of High Aspect Ratio Microcavities

The low electrode wear strategy based on a carbonaceous layer formation on electrodes considerably increases resource efficiency in the conventional die-sinking EDM. However, the smallest electrode projection area Ap for using the strategy is limited to 0.1 mm2 and maximum pulse current 3A, possibly due to the pulse re-opening phenomenon. In this work, using a novel generator circuit, pulse re-openings have been restricted up to pulse durations 100μs and a current of 1A. Hence, the performance of conventional electrode materials is evaluated in order to push the limits of the low wear strategy. However, when using graphite and copper infiltrated graphite microelectrodes, bending of the electrodes is observed, especially in the tip region. The simulation of temperature in the microelectrodes suggests abnormal carbonaceous build up process. This explanation is also concurrent to the observation of a process instability resulting in irreproducible electrode wear behaviour. For copper microelectrodes, another phenomenon is observed where overcuts are produced in the eroded cavities. These overcuts are produced by sparks with high discharge voltage. Sliding of the plasma channel from the electrode corners to the side surfaces is proposed to cause such discharges and overcuts. Thus, underlying mechanisms limiting the low wear strategy in micro-EDM are identified.

Amperometric determination of hydrogen peroxide using a copper microelectrode

The cathodic reduction of hydrogen peroxide at copper microelectrodes was investigated in phosphate buffer solutions.

Influence of Copper Ion Concentration on the Kinetics of Formation of a Protective Layer on Copper in an Acidic CMP Solution Containing BTA and Glycine

Copper chemical mechanical planarization (CMP) depends for its efficacy on many parameters, including the need for the solution to passivate the surface of copper. The influence of copper ions on the formation of such protective layers in an acidic solution containing BTA and glycine was investigated using potential-step chronoamperometry using two types of copper microelectrode, namely a three dimensional and a planar electrode. After stepping the potential of the copper electrodes to 0.6 V SHE, the measured current decayed as the protective layer was progressively formed. However, with concentrations of Cu(NO3)2 exceeding 0.1 mM, the current declined to a minimum, and subsequently increased. This behavior is attributed to the homogeneous nucleation and growth of Cu(II)BTA2 precipitates in the boundary layer near the copper surface. For prolonged chronoamperometry at 0.6 mM of Cu(NO3)2, the current began to decrease again after 100 seconds. This is thought due to the growth of bulk CuBTA2 precipitates toward the copper surface and repassivation of the surface. The increase in current due to homogeneous precipitation implies unsuccessful protection of the copper surface. This situation could easily arise during copper CMP. Thus, for effective CMP it is clearly necessary to control the concentration of copper ions in the solution.

SECM Studies on the Electrocatalytic Oxidation of Glycerol at Copper Electrodes in Alkaline Medium

AbstractThis study aims at analyzing the reaction mechanism of the electrooxidation of glycerol at copper surfaces in NaOH solutions using Scanning Electrochemical Microscopy (SECM) in the substrate generation/tip collection (SG/TC) mode. Experiments showed the dependence of the current at the tip on the distance between generator and tip, as well as on the concentration of the NaOH solution. The current at the tip decreased significantly after addition of glycerol, as a result of the competition between diffusion of the free‐soluble Cu(III) species and its consumption during the diffusion in the solution. The determination of the analyte in a castor biodiesel sample employing a single copper microelectrode was carried out.