Search Results (28)

Four tertiary amines (tributylamine, tripentylamine, trihexylamine, triethanolamine) were investigated with a 25 μm platinum disc microelectrode in more organic solvents. In the commonly used inert solvent acetonitrile, the sigmoidal-shaped curves used were recorded, except for triethanolamine, which showed two current plateaus close to each other, indicating temporal blocking in this case. The really surprising results arose from studies in acetic acid and ethyl acetate. Due to the complete protonation in acetic acid, the significant shifts of oxidation potentials led to the acquisition of lower currents only with the rising parts also using the same potential window as in ethyl acetate, where the voltammograms had a sigmoidal shape. Triethanolamine exhibited significant electrode deactivation in ethyl acetate, leading to the appearance of peak-shaped curves, and the difference between the first and second voltammograms was large. The current difference between the first and second scans allowed consequences for acetic acid content in cases where it was small, as the choice of this parameter proved to be the best for the analytical task. On the other hand, the differences in the shape of voltammograms allowed for quantitative approximations. The observed phenomenon could be utilized only for the estimation of acetic acid content. Full article

The development of laminations and mineral composition significantly determine the quality of shale oil reservoirs. The quantitative characterization of lamination development indicators and accurate calculation of mineral composition are key issues in logging evaluation. The Shahejie Formation continental shale oil reservoir in the Nanpu Sag, Bohai Bay Basin, was taken as a case study. Based on electrical imaging logging data, a high-pass filter was designed using the Chebyshev optimal approximation method to extract high-frequency information from the microelectrode curves of the electrical images. A high-resolution quantitative characterization method for millimeter-scale laminated structures of laminae was established, which improved the resolution by 2 to 3 times compared to the static and dynamic image resolutions of electrical imaging. By constructing lamination indices to characterize the sedimentary structural features of reservoirs, we effectively enhanced the fine recognition capability of electrical imaging logging data for sedimentary structures. Utilizing stratigraphic elemental well-log data, we employed an elemental–mineral component conversion model and optimized iterative techniques for accurate mineral composition calculation. We constructed a lithofacies classification scheme based on well-log data using the “rock types + sedimentary structures “approach, combined with research findings on lithofacies identification from well logs, and we identified 12 lithofacies types in the continental shale oil reservoirs of the Nanpu Sag, achieving fine-grained lithofacies logging identification across the entire area. The detailed lithofacies logging classification results were consistent with fine core descriptions. Full article

Various organic compounds susceptible to anodic polymerization were selected to study the effects of two solvents: acetic acid and ethyl acetate. Phenol and most of its derivatives, as well as resorcinol and 3,5-dihydroxybenzoic acid, exhibited typical electrode deactivation similar to other solvents; however, a continuous decrease in peak currents was not observed for 4-tert-butylphenols or salicylic aldehyde. Similar behavior was noted for monomers unrelated to phenols. In general, peaks were observed only for certain compounds and not in the initial voltammogram. Significant differences between the two solvents were observed in the subsequent voltammetric curves for some monomers. Microelectrode studies using 4-methoxyphenol as a model compound revealed notable differences between acetic acid and ethyl acetate in terms of curve shapes and the onset potentials of the plateaus. Plateau currents were used to estimate the solvent composition, demonstrating relatively high sensitivity to the acetic acid content. Full article

Molybdenum is an important material in modern industry, widely used in extreme environments such as rocket engine nozzles and microelectrodes due to its high melting point, excellent mechanical properties, and thermal conductivity. However, as a difficult-to-machine metal, traditional machining methods struggle to achieve the desired microstructures in molybdenum. Electrochemical machining (ECM) offers unique advantages in manufacturing fine structures from hard-to-machine metals. Studies have shown that molybdenum exhibits a fast corrosion rate in alkaline or acidic solutions, posing significant environmental pressure. Therefore, this study investigates the electrochemical machining of molybdenum in neutral salt solutions to achieve high-precision microstructure fabrication. First, the polarization curves and electrochemical impedance spectroscopy (EIS) of molybdenum in NaNO3 solutions of varying concentrations were measured to determine its electrochemical reaction characteristics. The results demonstrate that molybdenum exhibits good electrochemical reactivity in NaNO3 solutions, leading to favorable surface erosion morphology. Subsequently, a mask electrochemical machining technique was employed to fabricate arrayed microstructures on the molybdenum surface. To minimize interference between factors, an orthogonal experiment was used to optimize the parameter combination, determining the optimal machining process parameters. Under these optimal conditions, an array of micro-groove structures was successfully fabricated with an average groove width of 110 μm, a depth-to-width ratio of 0.21, an aspect ratio of 9000, and a groove width error of less than 5 μm. Full article

Neurotoxic heavy metals, such as Cd²⁺, pose a significant global health concern due to their increased environmental contamination and subsequent detrimental health hazards they pose to human beings. These metal ions can breach the blood-brain barrierblood–brain barrier, leading to severe and often irreversible damage to the central nervous system and other vital organs. Therefore, developing a highly sensitive, robust, and rapid in vivo detection method for these hazardous heavy metal ions is of the utmost importance for early detection, thus initiating timely therapeutics. Detecting ultra-low levels of toxic metal ions in vivo and obtaining accurate speciation information remains a challenge with conventional analytical techniques. In this study, we fabricated a novel carbon carbon-fiber microelectrode (CFM)-based sensor that can detect Cd²⁺ ions using fast-scan cyclic voltammetry by electrodepositing gold nanoparticles (AuNP). We optimized electrochemical parameters that generate a unique cyclic voltammogram (CV) of Cd²⁺ at a temporal resolution of 100 ms with our novel sensor. All our experiments were performed in tris buffer that mimics the artificial cerebellum fluid. We established a calibration curve resulting in a limit of detection (LOD) of 0.01 µM with a corresponding sensitivity of 418.02 nA/ µM. The sensor’s selectivity was evaluated in the presence of other metal ions, and it was noteworthy to observe that the sensor retained its ability to produce the distinctive Cd²⁺ CV, even when the concentration of other metal ions was 200 times higher than that of Cd²⁺. We also found that our sensor could detect free Cd²⁺ ions in the presence of complexing agents. Furthermore, we analyzed the solution chemistry of each of those Cd²⁺–ligand solutions using a geochemical model, PHREEQC. The concentrations of free Cd²⁺ ions determined through our electrochemical data align well with geochemical modeling data, thus validating the response of our novel sensor. Furthermore, we reassessed our sensor’s LOD in tris buffer based on the concentration of free Cd²⁺ ions determined through PHREEQC analysis, revealing an LOD of 0.00132 µM. We also demonstrated the capability of our sensor to detect Cd²⁺ ions in artificial urine samples, showcasing its potential for application in actual biological samples. To the best of our knowledge, this is the first AuNP-modified, CFM-based Cd²⁺ sensor capable of detecting ultra-low concentrations of free Cd²⁺ ions in different complex matrices, including artificial urine at a temporal resolution of 100 ms, making it an excellent analytical tool for future real-time, in vivo detection, particularly in the brain. Full article

We propose to study the nonlinear stroke and lower-order modal interactions of a clamped–clamped shallow-arch flexible micro-electrode. The flexible electrode is electrically actuated through an in-plane parallel-plates field superimposed over out-of-plane electrostatic fringing fields. The in-plane electrostatic fields result from a difference of potential between the initially curved flexible electrode and a lower stationary parallel-grounded electrode. Moreover, the out-of-plane fringing fields are mainly due to the out-of-plane asymmetry of the flexible shallow arch and two respective surrounding stationary side electrodes (left and right). A nonlinear beam model is first introduced, consisting of a nonlinear partial differential equation governing the flexible shallow-arch in-plane deflection. Then, a resultant reduced-order model (ROM) is derived assuming a Galerkin modal decomposition with mode-shapes of a clamped–clamped beam as basis functions. The ROM coupled modal equations are numerically solved to obtain the static deflection. The results indicate the possibility of mono-stable and bi-stable structural behaviors for this particular device, depending on the flexible electrode’s initial rise and the size of its stationary side electrodes. The eigenvalue problem is also derived and examined to estimate the variation of the first three lower natural frequencies of the device when the microbeam is electrostatically actuated. The proposed micro-device is tunable with the possibility of pull-in-free states in addition to modal interactions through linear coupled mode veering and crossover processes. Remarkably, the veering zone between the first and third modes can be electrostatically adjusted and reach $22.6$kHz for a particular set of design parameters. Full article

The rise in diabetes cases is a growing concern due to the aging of populations. This not only places a strain on healthcare systems but also creates serious public health problems. Traditional blood tests are currently used to check blood sugar levels, but they are invasive and can discourage patients from regularly monitoring their levels. We recently developed nano-sensing probes that integrate Au microelectrodes and conductivity meters, requiring only 50 μL of saliva for measurement. The usage of the co-planar design of coating-free Au electrodes makes the measurement more stable, precise, and easier. This study found a positive correlation between the participant’s fasting blood sugar levels and salivary conductivity. We observed a diabetes prevalence of 11.6% among 395 adults under 65 years in this study, using the glycated hemoglobin > 6.5% definition. This study found significantly higher salivary conductivity in the diabetes group, and also a clear trend of increasing diabetes as conductivity levels rose. The prediction model, using salivary conductivity, age, and body mass index, performed well in diagnosing diabetes, with a ROC curve area of 0.75. The study participants were further divided into low and high groups based on salivary conductivity using the Youden index with a cutoff value of 5.987 ms/cm. Individuals with higher salivary conductivity had a 3.82 times greater risk of diabetes than those with lower levels, as determined by the odds ratio calculation. In conclusion, this portable sensing device for salivary conductivity has the potential to be a screening tool for detecting diabetes. Full article

Liquid biopsy is a rapidly emerging field that involves the minimal/non-invasive assessment of signature somatic mutations through the analysis of circulating tumor DNA (ctDNA) shed by tumor cells in bodily fluids. Broadly speaking, the unmet need in liquid biopsy lung cancer detection is the lack of a multiplex platform that can detect a mutation panel of lung cancer genes using a minimum amount of sample, especially for ultra-short ctDNA (usctDNA). Here, we developed a non-PCR and non-NGS-based single-droplet-based multiplexing microsensor technology, “Electric-Field-Induced Released and Measurement (EFIRM) Liquid Biopsy” (m-eLB), for lung cancer-associated usctDNA. The m-eLB provides a multiplexable assessment of usctDNA within a single droplet of biofluid in only one well of micro-electrodes, as each electrode is coated with different probes for the ctDNA. This m-eLB prototype demonstrates accuracy for three tyrosine-kinase-inhibitor-related EGFR target sequences in synthetic nucleotides. The accuracy of the multiplexing assay has an area under the curve (AUC) of 0.98 for L858R, 0.94 for Ex19 deletion, and 0.93 for T790M. In combination, the 3 EGFR assay has an AUC of 0.97 for the multiplexing assay. Full article

The success rate in vitro fertilization is significantly linked to the quality of the oocytes. The oocyte’s membrane is encapsulated by a shell of gelatinous extracellular matrix, called zona pellucida, which undergoes dynamic changes throughout the reproduction cycle. During the window of highest fertility, the zona pellucida exhibits a softening phase, while it remains rigid during oocyte maturation and again after fertilization. These variations in mechanical properties facilitate or inhibit sperm penetration. Since successful fertilization considerably depends on the state of the zona pellucida, monitoring of the hardening process of the zona pellucida is vital. In this study, we scrutinized two distinct genetic mouse models, namely, fetuin-B wild-type and fetuin-B/ovastacin double deficient with normal and super-soft zona pellucida, respectively. We evaluated the hardening with the help of a microfluidic aspiration-assisted electrical impedance spectroscopy system. An oocyte was trapped by a microhole connected to a microfluidic channel by applying suction pressure. Transient electrical impedance spectra were taken by microelectrodes surrounding the microhole. The time-depending recovery of zona pellucida deflections to equilibrium was used to calculate the Young’s modulus and, for the first time, absolute viscosity values. The values were obtained by fitting the curves with an equivalent mechanical circuit consisting of a network of dashpots and springs. The observer-independent electrical readout in combination with a fitting algorithm for the calculation of the viscoelastic properties demonstrates a step toward a more user-friendly and easy-to-use tool for the characterizing and better understanding of the rheological properties of oocytes. Full article

The thermal insulation and integrity of the thermal barrier coating is hampered by the formation of mixed oxide at intermediate bond coat. The existing reported work correlates growth of mixed oxide to the microstructural and phase changes. The track mostly used to study these changes is scanning electron microscopy, X-ray diffraction, and electrochemical testing. Oxide growth is principally an electrochemical process; hence a thirst exists to study this aspect by using advanced electrochemical techniques. In this study scanning electrochemical microscopy is used to reveal the electrochemical activity in the closest vicinity of the surface. A raster scan of 500 µm area was carried out by microelectrode in an electrolyte at a distance of 5 µm above the surface to record the current profile. The activity at the surface was confirmed by current distance curves. The tip of the microelectrode was approached from 60 µm height to 2 µm above the surface. The current–distance curves for the coating without heat-treatment show an active surface while the heat-treated one show non active surface. The average coating electrochemical response was further studied by polarization curves impedance spectroscopy. The X-ray photoelectron spectroscopy results show that oxidation and formation of the mixed oxide increase with polarization. Full article

Cathodic protection efficiency of complex carbon steel structures in confined seawater environment was studied using a specific experimental device. Schematically, this device consisted of a Plexiglas matrix, crossed by a channel 50 cm long, 5 mm deep, 1.5 to 5 cm wide, which moreover included four bends at 90°. Seawater flowed continuously inside the channel over 12 steel coupons embedded in the Plexiglas matrix. Cathodic protection was applied at a constant potential of −1060 mV vs. Ag/AgCl-seawater with respect to a reference electrode located outside the channel, at the seawater flow entry. The potential of four selected coupons was monitored over time via a microelectrode set close to each coupon. It varied significantly with the distance separating the coupons from the channel entry. At the end of the 3.5-month experiment, a polarization curve was acquired. The residual corrosion rate under cathodic protection was estimated via the extrapolation of the anodic Tafel line. It varied from <1 µm yr⁻¹ to 16 µm yr⁻¹, depending on the potential reached by the coupon (between −900 and −1040 mV vs. Ag/AgCl-seawater) at the end of the experiment and on the properties of the calcareous deposit formed on the steel surface. Full article

The method to diagnose mastitis is generally the somatic cell count (SCC) by flow cytometry measurement. When the number of somatic cells in raw milk is 2.0 × 10⁵ cells/mL or more, the condition is referred to as mastitis. In the current study, we created a milk cell chip that serves as an electrochemical method that can be easily produced and used utilizing scanning electrochemical microscopy (SECM). The microelectrode present in the cell chip scans, and the difference between the oxygen concentration near the milk cell chip and in bulk is measured as the oxygen (O₂) reduction current. We estimated the relationship between respiratory activity and the number of somatic cells in raw milk as a calibration curve, using scanning electrochemical microscopy-somatic cell count (SECM-SCC). As a result, a clear correlation was shown in the range of 10⁴ cells/mL to 10⁶ cells/mL. The respiration rate (F) was estimated to be about 10–16 mol/s per somatic cell. We also followed the increase in oxygen consumption during the respiratory burst using differentiation inducer phorbol 12-myristate 13-acetate (PMA) as an early stage of mastitis, accompanied with an increase in immune cells, which showed similar results. In addition, we were able to discriminate between cattle with mastitis and without mastitis. Full article

Scanning electrochemical microscopy (SECM) used in the feedback mode is one of the most powerful versatile analytical tools used in the field of battery research. However, the application of SECM in the field of lithium-ion batteries (LIBs) faces challenges associated with the selection of a suitable redox mediator due to its high reactivity at low potentials at lithium metal or lithiated graphite electrodes. In this regard, the electrochemical/chemical stability of 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB) is evaluated and benchmarked with ferrocene. This investigation is systematically carried out in both linear and cyclic carbonates of the electrolyte recipe. Measurements of the bulk current with a microelectrode prove that while DBDMB decomposes in ethyl methyl carbonate (EMC)-containing electrolyte, bulk current remains stable in cyclic carbonates, ethylene carbonate (EC) and propylene carbonate (PC). Ferrocene was studied as an alternative redox mediator, showing superior electrochemical performance in ethyl methyl carbonate-containing electrolytes in terms of degradation. The resulting robustness of ferrocene with SECM is essential for a quantitative analysis of battery materials over extended periods. SECM approach curves depict practical problems when using the decomposing DBDMB for data acquisition and interpretation. This study sheds light towards the use of SECM as a probing tool enabled by redox mediators. Full article

The double-layer blanket (DLB) reverse offset is a newly designed printing process for patterning electronic circuits on a 3D curved surface. Unlike the existing reverse offset process, the DLB reverse offset utilizes an offset roll composed of two layers comprising polydimethylsiloxane (PDMS) and a thick, soft cushioned rubber to print microelectrode patterns and transparent electrodes on a curved surface. The optimal printing process was determined by adjusting the printing pressure and printing speed for horizontal and vertical micropatterns, based on which transparent electrodes with metal mesh and honeycomb structures with a line width of 30 μm and pitch of 600 μm with micropatterns ranging from 30 μm to 60 μm were printed on a curved surface. Ag ink was used, and the 3D curved surface indicated a print quality similar to that of the flat surface for both the vertical and horizontal patterns and transparent electrodes. The DLB reverse offset technique demonstrated the possibility of printing on a 3D curved surface and is expected to broaden the range of printed electronics to applications such as smart glasses and 3D shape sensors. Full article

Small; lithographically-defined and closely-spaced metallic features of dimensions and separation in the micrometer range are of strong interest as working and counter electrodes in compact electrochemical sensing devices. Such micro-electrode systems can be integrated with microfluidics and optical biosensors, such as surface plasmon waveguide biosensors, to enable multi-modal sensing strategies. We investigate lithographically-defined gold and platinum micro-electrodes experimentally, via cyclic voltammetry (CV) measurements obtained at various scan rates and concentrations of potassium ferricyanide as the redox species, in potassium nitrate as the supporting electrolyte. The magnitude of the double-layer capacitance is estimated using the voltammograms. Concentration curves for potassium ferricyanide are extracted from our CV measurements as a function of scan rate, and could be used as calibration curves from which an unknown concentration of potassium ferricyanide in the range of 0.5–5 mM can be determined. A blind test was done to confirm the validity of the calibration curve. The diffusion coefficient of potassium ferricyanide is also extracted from our CV measurements by fitting to the Randles–Sevcik equation (D = 4.18 × 10⁻¹⁰ m²/s). Our CV measurements were compared with measurements obtained using macroscopic commercial electrodes, yielding good agreement and verifying that the shape of our CV curves do not depend on micro-electrode geometry (only on area). We also compare our CV measurements with theoretical curves computed using the Butler–Volmer equation, achieving essentially perfect agreement while extracting the rate constant at zero potential for our redox species (k^o = 10⁻⁶ m/s). Finally, we demonstrate the importance of burn-in to stabilize electrodes from the effects of electromigration and grain reorganization before use in CV measurements, by comparing with results obtained with as-deposited electrodes. Burn-in (or equivalently, annealing) of lithographic microelectrodes before use is of general importance to electrochemical sensing devices Full article