Preparation Of Microelectrodes Research Articles

Preparation of microelectrode based on molecularly imprinted monolith using ionic liquids as functional monomers for specific separation and enrichment of phenolic acids

Efficient and specific isolation and capture of phenolic acids (PAs) in complex samples is challenging due to its high polarity. In this study, combining the merits of porous monolith, ionic liquids, molecularly imprinted polymer and electroenhanced solid-phase microextraction (EE-SPME), a new sample pretreatment method was developed for the selective isolation and extraction of PAs. Using vanillic acid (VA) as template molecule, mixed ionic liquids including 1-allyl-3-methylimidazoliumbis[(trifluoromethy)sulfonyl]imide and N,N,N-trimethyl-1-(4-vinylphenyl)methanaminium chloride were chosen as dual functional monomers, a molecularly imprinted monolith-based microelectrode (MBM) was in-situ fabricated. Under the EE-SPME format, the extraction behaviors and specific recognition performance of MBM towards VA and its structural analogues were investigated in detail. Results revealed that the exertion of electric field during extraction period increased the imprinted factors from 1.57–1.77 to 1.87–2.23. Under the beneficial parameters, a sensitive and reliable approach for the quantification of PAs contents in water and fruit juice samples by the combination of MBM/EE-SPME with HPLC technique was developed. The achieved limits of detection ranging from 0.012 μg/L to 0.11 μg/L and 0.042 μg/L to 0.15 μg/L for waters and juices, respectively, and the recoveries with different spiked concentrations in actual sample were 83.1–110 %. In comparison with the existing approaches, the established method presented some characteristics in the analysis of PAs, such as simplicity, high cost-effectiveness, good anti-interference performance, satisfactory sensitivity and low consumption of solvent.

Sinking ECDM micro-milling of micro-channels with a customized electrode

ABSTRACT Electrochemical discharge machining (ECDM) micro-milling exhibits enormous machining potential in manufacturing metal microstructures. In this paper, a novel sinking ECDM micro-milling using glycol-based electrolyte is proposed for the high-quality fabrication of metal micro-channel structures. Firstly, a novel combined process is developed for the simple and efficient preparation of micro-electrode. With the proposed method, a micro-electrode with 91.1 μm in diameter and 21.2:1 in aspect ratio is successfully machined in 47.2 minutes. Secondly, experimental research on ECDM micro-milling machining of micro-channels in glycol-based electrolyte is carried out using the fabricated micro-electrode. Experimental results show that the machined voltage significantly affects the machining quality of micro-channels. Wear analysis reveals that the bottom geometry of the micro-electrode exhibits equal wear along the axis direction with processing times increasing, and a constant length compensation strategy (1.52 μm/mm) is adopted. Finally, an S-shaped micro-channel without recast layers (Ra 0.093 μm) was successfully fabricated.

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.

Fabrication of Fe-based metal glass microelectrodes by a vertical liquid membrane electrochemical etching method.

The excellent physical and chemical properties of metallic glasses and the absence of crystal defects make them ideal materials for the preparation of microelectrodes. A vertical liquid membrane electrochemical etching method is proposed here for the fabrication of microelectrodes from the Fe-based metallic glass Fe77.5B15Si7.5. With this method, insoluble electrolysis products are kept away from the processing area, and the nonuniformity of the diffusion layer that occurs in traditional transverse liquid membrane electrochemical etching is reduced. Simulations of the potential distribution and the current density distribution are carried out in COMSOL software, and the simulation results are verified by experiments. The passivation characteristics of the Fe77.5B15Si7.5 metallic glass in H2SO4 and H3PO4 electrolytes are studied. The effects of processing voltage on electrode morphology and surface quality are studied experimentally. Micropins with good tip size can be prepared in the active dissolution stage in 0.1M H2SO4 solution, and high-aspect-ratio cylindrical microtool electrodes with high surface quality can be fabricated in the transpassivation stage in 80% H3PO4 electrolyte with high machining stability.

Nanoparticle Characterization Through Nano-Impact Electrochemistry: Tools and Methodology Development.

The field of nanomaterials has been expanding rapidly into many diverse applications within the last 20years. With this growth, there is a significant need for new method development for the detection and characterization of nanomaterials. Understanding the physical properties of nanoscale entities and their associated reaction kinetics is crucial for monitoring their effect on environmental and human health, and in their use for practical applications. Nano-impact electrochemistry is a novel development in the field of fundamental electrochemistry that provides an ultrasensitive method for analyzing physical and redox properties of nanomaterials and their derivatives. This protocol focuses on the tools required for characterizing silver nanoparticles (AgNPs) by nano-impact electrochemistry, the preparation of microelectrodes and the methodology needed for measurement of the AgNP redox activity. The fabrication of cylindrical carbon fiber as well as gold and platinum microwire electrodes is described in detail. The analysis of nano-impact electrochemistry for the characterization of redox active entities is also outlined with examples of applications.

<i>In Situ</i>: A Novel Approach for the Production of Micro Holes

This work is on the preparation of microelectrodes for μ-EDM operation using μ-WEDG process. Electrodes of Ø500 μm are fabricated with various discharge energy machining conditions. Effects of gap voltage, capacitance & feed rate on the surface finish of the electrodes and overcut of the thus produced micro holes are investigated. The profile of microelectrodes is measured using surface roughness tester with 2μm stylus interfaced with SURFPAK software. The study demonstrated that for brass electrodes an arithmetic average roughness value as low as 1.7μm and an overcut of 3 µm could be achieved. The significant machining parameters are found using ANOVA. Surface of the produced microelectrodes are examined using Scanning Electron Microscope. μ-WEDG process parameters could be adjusted to achieve good surface integrity on microelectrodes. Experimental results showed that the surface roughness of microelectrodes depended primarily on feed rate of the electrode. The observations showed the clear and quantitative correlation existing between the micrometer level surface quality and process parameters. The resulting microelectrodes are found to be of exceptionally high quality and could be used for μ- EDM operation on different types of work materials.

Insulating method using cataphoretic paint for tungsten tips for electrochemical scanning tunnelling microscopy (ECSTM)

A new tip insulating process for active metal tips allowing atomic resolution ECSTM imaging has been developed. This new method using cathodic cataphoretic paint deposition has been tested successfully. The insulating deposited film appears homogeneous under optical microscopy and it has been characterised by infra red and SEM analysis. The depositing layer of the paint is sufficiently dense to effectively resist electrolyte ion penetration and resists corrosion in various acidic, basic aqueous or non-aqueous media. The coating film does not reduce the imaging capability of the ECSTM even to atomic resolution. This new insulating method adds to the approaches available to those preparing tips for ECSTM. This approach would also be of great utility for the preparation of microelectrodes using active metals.

Overcoming the Problem of Non-Ideal Liquid Ion Exchanger Selectivity in Microelectrode Ion Flux Measurements

Ion-selective microelectrodes are a powerful tool in studies on various aspects of cell membrane biology in both animal and plant tissues. Further application of this technique is, however, limited to a large extent by the problem of non-ideal selectivity of the liquid ion exchanger used in the preparation of microelectrodes for ion flux measurements. Because of this problem, which is persistent in many commercial liquid ion exchangers, the microelectrode does not discriminate between the ion of interest and other interfering ions (for example, Mg2+ and Ca2+; Na+ and K+), thereby leading to inaccurate concentration readings and, consequently, inaccurate flux calculations. In this work we show that the existing analytical procedure to overcome this problem, using the inverted Nicolsky-Eisenman equation, is inadequate, and suggest an alternative analytical procedure that can be applied directly to the data obtained with commercially available liquid ion exchangers. We show that this alternative procedure allows accurate measurement of ionic concentrations with non-ideal ion-selective microelectrodes in the presence of interfering ions, and illustrate the method by direct experiment using Ca2+ and Mg2+ as a "case study". Several more examples are given, further illustrating practical applications of the method for study of plant responses to salinity, osmotic and reactive oxygen species stresses.

Microelectrodes for in situ voltammetric determination of pollutants

The toxicity of sediments is often closely bound to the labile toxic elements contents. In porewaters, metal concentrations are generally measured after separation from the solid material by means of pressure or centrifugation. The recent developments of in situ metal measurements by microsensors do not require any pretreatment of the sediment and hence avoid some possible artefacts like oxygen penetration in anoxic sediment and/or temperature modification. The work describes firstly the preparation of microelectrodes based on a thin solid Silver (diameter: 30 μm) or Iridium (diameter: 75 μm) wire, covered at the tip with a fine layer of mercury. Secondly, an analytical procedure (based on cathodic voltammetry) is presented to measure Mn(II), Fe(II) and S(-II) concentrations, which play a relevant role in the metal pollutant cycle in sediments. By anodic stripping voltammetry, such microsensors are able to detect trace heavy metals such as Cd(II) or Pb(II) at relatively low concentration levels (∼1 μg/dm 3 ) with 5 minutes accumulation time. Finally, the most important challenge is to install the microelectrodes in natural media and to follow up metal pollution over a long time period.

Preparation of a Gold‐Sputtered Optical Fiber as a Microelectrode for Electrochemical Microscopy

The preparation of microelectrodes for use in various electrochemical mapping techniques (e.g., scanning electro‐chemical microscopy and photoelectrochemical microscopy) is described. A commercial optical fiber (3.7 μm core diameter with and diam of cladding and coating, respectively) was stripped of its polymer coating at one end. The stripped core was then etched in different concentrations of hydrofluoric acid solution until a tip near 1 μm in diameter was achieved. The resulting optical fiber was coated with gold by de‐sputtering to produce a microelectrode less than 3 μm in total diameter. The optical fiber microelectrode was then coated with an insulating varnish yielding a final tip size normally less than 5 μm in diam. The final microelectrode was tested both for leaks in its polymer insulation and for electrical conductivity of the gold coating. The microelectrode has been used in several studies in our laboratories. Details of the preparation conditions are described here.

Preparation of microelectrodes: comparison of polishing procedures by statistical analysis of voltammetric data

Manual and instrumental procedures for polishing 1 and 6 µm radius platinum microdisc electrodes were compared by performing a statistical evaluation of three basic electrochemical signal characteristics measured from steady-state voltammograms for oxidation of ferrocene in acetonitrile. The three signal characteristics measured were the limiting current Ilim, the half-wave potential E1/2 and the (E3/4–E1/4) potential difference, where E3/4 and E1/4 are the potentials at three quarters Ilim and one quarter Ilim, respectively. Fisher–Snedeckor F-test and Student's t-test statistical data are presented together with corresponding critical values for the three electrochemical parameters obtained in the manual and instrumental polishing modes. The reproducibility of all measured data is significantly improved when the electrode is polished after each experiment. The mean values of the limiting currents were significantly better using the instrumental rather than the manual polishing method. However, with respect to uncertainty of the experimental values, instrumental polishing gave the best estimates of the measured parameters; confidence intervals were very small for E1/2 and (E3/4–E1/4) potential measurements, being ±0.20 and ±0.36 mV for E1/2 values and 0.11 and 0.19 mV for (E3/4–E1/4) at 1 and 6 µm electrodes, respectively. The instrument designed for polishing microelectrodes is also described.

Electrochemical preparation of microelectrodes modified with non-stoichiometric mixed-valent molybdenum oxides

A blue, conductive, compact, mixed-valent Mo(VI, V) oxide film was grown on carbon fiber (CF) microelectrode surface by cycling the potential between + 0.20 and −0.70 V vs. SCE in a fresh prepared Na 2MoO 4 solution (pH = 2, H 2SO 4). The thickness of the oxide film was controlled by charge passing through. X-ray photoelectron energy spectra (XPS) confirmed that the products of molybdenum oxide film coating on the CF electrode surface are mainly a mixture of Mo 6+ and Mo 5+ complex, meanwhile a little of Mo 4+ exists in the film, but the Mo 3+ peak was not observed in XPS. Well-defined redox transitions have been attributed to the reductive formation of hydrogen molybdenum bronzes [MoO 3−x(OH) x] and reoxidation in acidic media. The coating is easily permeable to ions. The molybdenum oxide film catalyses the electroreduction of chlorate to chloride and bromate to bromide in H 2SO 4.

Microperforation with laser beam in the preparation of microelectrodes.

Using a laser beam, spot perforations have been made in the vinyl lacquer insulation of tungsten microelectrodes. To develop the method, the effect of the diffraction of the laser beam on the diameter of the burning point and of the geometric and diffractive conditions in the focusing of the beam have been examined, taking into account the small diameter of the electrode (about 10-15 μm) and the thinness of the insulating layer. Using the burning method described here, it has been possible to decrease the effective divergence angle of the laser beam so that the diameters of the holes which are formed on the electrode are mostly 2 μm or less. The burning point of the laser beam can be localized with the developed optical method to a desired point on the electrode. The perforation has been performed in saline immersion-liquid to protect the objective and to test immediately formed holes electrolytically. The burning apparatus and method have been explained.

Preparation of microelectrode for intracellular measurements: G. A. Kurella, Biofizika, 3, 243–245 (1958)

Preparation of microelectrode for intracellular measurements: G. A. Kurella, Biofizika, 3, 243–245 (1958)