Search Results (34)

The toxicity of emerging organic pollutants to photosystems of aquatic plants is still not well clarified. This study aimed to develop a novel ecotoxicological experimental protocol based on nanoscale electrochemical mapping of photosynthetic oxygen evolution of aquatic plants by scanning electrochemical microscopy (SECM). The protocol was also checked by confocal laser scanning microscopy (CLSM), the traditional Clark oxygen electrode method, and the chlorophyll fluorescence technique. The typical persistent organic pollutant 2,4-dichlorophenol (2,4-DCP) in a water environment and the common aquatic Microsorium pteropus (M. pteropus) were chosen as the model organic pollutant and tested plant, respectively. It was found that the SECM method could discriminate the responses of stoma micromorphology and spatial pattens of photosynthetic oxygen evolution on single stoma well. The shape of stoma blurred with increasing 2,4-DCP concentration, which was in good agreement with the CLSM images. The dose–response curves and IC₅₀ values obtained from the SECM data were verified by the data measured by the traditional Clark oxygen electrode method and chlorophyll fluorescence test. The IC₅₀ value of single-stoma oxygen emission of plant leaves exposed for 24 h, which was derived from the SECM current data (32,535 μg L⁻¹), was close to those calculated from the maximum photosynthetic efficiency (Fv/Fm) measured by the chlorophyll fluorescence test (33,963 μg L⁻¹) and the Clark oxygen electrode method photosynthetic oxygen evolution rate (32,375 μg L⁻¹). The 72 h and 96 h 2,4-DCP exposure data further confirmed the reliability of the nanoscale stoma oxygen emission mapping methodology for ecotoxicological assessment. In this protocol, the procedures for how to collect effective electrochemical data and how to extract useful information from the single-stoma oxygen emission pattern were well established. This study showed that SECM is a feasible and reliable ecotoxicological tool for evaluation of toxicity of organic pollutants to higher plants with a unique nanoscale visualization advantage over the conventional methods. Full article

Chemical imaging of corrosion processes involving copper species using scanning electrochemical microscopy has been hampered by the lack of soluble oxidation states for copper that can be achieved by amperometric conversion at the tip. Indeed, the only possibility is to reduce the corrosion products at the tip, thus modifying the chemical response of the electrode material and requiring subsequent redissolution of the copper deposits. Consequently, the limitations arising from the system prevented a full-scale quantification, requiring the development of new methodologies or the optimisation of those currently available, as we pursued with the present work. Therefore, the voltammetric behaviours of gold macro- and microelectrodes were evaluated with respect to the collection and redissolution of Cu²⁺ ions, with the aim of using them as sensing probes in scanning electrochemical microscopy (SECM) to investigate the activity of copper surfaces in acidic chloride-containing environments. Cyclic and square-wave voltammetric techniques were explored for copper collection and subsequent stripping on Au microelectrode tips in SECM with the objective to capture in situ image electrochemical reactivity distributions across copper surfaces undergoing corrosion. Full article

Scanning electrochemical microscopy (SECM) is a type of scanning probe microscopy (SPM) where an electrochemical reaction at a microelectrode is used to generate information about an electrochemically (in)active surface in its immediate vicinity. Careful preparation and knowledge of the microelectrode response as well as the application of a suitable method enable the study of spatially resolved electrochemical kinetics or the electrocatalytic activity of any structure or material. In addition to a wide range of other applications, the method has become particularly well established in the research field of electrochemical energy storage and conversion. Full article

This work demonstrates an approach towards the understanding of multi-scale and open-circuit localised electrochemical processes of AA2024-T3 in the presence and absence of an environmentally friendly rare-earth inhibitor; cerium diphenyl phosphate (Ce(dpp)₃). At high temporal resolution, a wire bean electrode (WBE) made from 100 identical AA2024-T3 wires revealed sudden increases in galvanic anodic and cathodic activities immediately after dosing of 50 and 100 ppm of the inhibitor and an overall suppression of macro-scale activities by increasing the inhibitor concentration to 200 ppm, suggesting it as a fast-screening tool for inhibitors and measuring inhibition efficiency. At high spatial resolutions, scanning probe electrochemical techniques confirmed local activation of corroding microstructures on individual AA2024-T3 wires similarly by dosing the inhibitor up to 100 ppm. In agreement with WBE findings, the effective shutdown of both anodic and cathodic activities occurred after increasing the inhibitor concentration to 200 ppm confirming the optimal concentration of the Ce(dpp)₃ and the mixed mode inhibition mechanism of this selected inhibitor on AA2024-T3. Full article

This paper evaluated the use of soft-probe scanning electrochemical microscopy complementarily with confocal laser scanning microscopy to study the effects of different antimicrobial agents and treatments on E. coli DH5α biofilm. The antimicrobial agents were sodium azide, silver nanoparticles, and a flashlight. The effects of these agents were monitored by measuring the change in biofilm properties, such as biofilm biomass, live/dead studies, and surface activity. The results showed that sodium azide, silver nanoparticles, and the flashlight effectively killed E. coli biofilms and explained the mode of action for each treatment. Sodium azide was more effective in killing the biofilm after a short treatment time by blocking the ATPase, while silver nanoparticles were more effective at killing the biofilm after longer treatment times through several antibiofilm actions. This work showed that scanning electrochemical microscopy (SECM) is a very valuable tool for studying the effects of antimicrobial agents on biofilms. SECM is a sensitive technique that can be used to monitor the changes in biofilm properties in real-time. Additionally, SECM does not require any sample preparation, which makes it a convenient and efficient technique. Overall, the results of this study could be used to develop new strategies for treating E. coli biofilm infections and provide valuable insights into the use of SECM to study the effects of antimicrobial agents on E. coli biofilms. Full article

Bacteria are similar to social organisms that engage in critical interactions with one another, forming spatially structured communities. Despite extensive research on the composition, structure, and communication of bacteria, the mechanisms behind their interactions and biofilm formation are not yet fully understood. To address this issue, scanning probe techniques such as atomic force microscopy (AFM), scanning electrochemical microscopy (SECM), scanning electrochemical cell microscopy (SECCM), and scanning ion-conductance microscopy (SICM) have been utilized to analyze bacteria. This review article focuses on summarizing the use of electrochemical scanning probes for investigating bacteria, including analysis of electroactive metabolites, enzymes, oxygen consumption, ion concentrations, pH values, biofilms, and quorum sensing molecules to provide a better understanding of bacterial interactions and communication. SECM has been combined with other techniques, such as AFM, inverted optical microscopy, SICM, and fluorescence microscopy. This allows a comprehensive study of the surfaces of bacteria while also providing more information on their metabolic activity. In general, the use of scanning probes for the detection of bacteria has shown great promise and has the potential to provide a powerful tool for the study of bacterial physiology and the detection of bacterial infections. Full article

In this paper, the applicability of Ti6Al7Nb as a more biocompatible alternative for bone and dental implants than Ti6Al4V and pure titanium in terms of corrosion resistance and electrochemical inertness is investigated. The chemical inertness and corrosion resistance of the Ti6Al7Nb biomaterial were characterized by a multi-scale electrochemical approach during immersion in simulated physiological environments at 37 °C comparing its behavior to that of c.p. Ti, Ti6Al4V, and stainless steel. The establishment of a passive regime for Ti6Al7Nb results from the formation of a thin layer of metal oxide on the surface of the material which prevents the action of aggressive species in the physiological medium from direct reaction with the bulk of the alloy. Conventional electrochemical methods such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) provide quantified information on the surface film resistance and its stability domain that encompasses the potential range experienced in the human body; unfortunately, these methods only provide an average estimate of the exposed surface because they lack spatial resolution. Although local physiological environments of the human body are usually simulated using different artificial physiological solutions, and changes in the electrochemical response of a metallic material are observed in each case, similar corrosion resistances have been obtained for Ti6Al7Nb in Hank’s and Ringer’s solutions after one week of immersion (with a corrosion resistance of the order of MΩ cm²). Additionally, scanning electrochemical microscopy (SECM) provides in situ chemical images of reactive metal and passive dielectric surfaces to assess localized corrosion phenomena. In this way, it was observed that Ti6Al7Nb exhibits a high corrosion resistance consistent with a fairly stable passive regime that prevents the electron transfer reactions necessary to sustain the metal dissolution of the bulk biomaterial. Our results support the proposition of this alloy as an efficient alternative to Ti6Al4V for biomaterial applications. Full article

Scanning electrochemical microscopy (SECM) is a versatile scanning probe technique that allows monitoring of a plethora of electrochemical reactions on a highly resolved local scale. SECM in combination with atomic force microscopy (AFM) is particularly well suited to acquire electrochemical data correlated to sample topography, elasticity, and adhesion, respectively. The resolution achievable in SECM depends critically on the properties of the probe acting as an electrochemical sensor, i.e., the working electrode, which is scanned over the sample. Hence, the development of SECM probes received much attention in recent years. However, for the operation and performance of SECM, the fluid cell and the three-electrode setup are also of paramount importance. These two aspects received much less attention so far. Here, we present a novel approach to the universal implementation of a three-electrode setup for SECM in practically any fluid cell. The integration of all three electrodes (working, counter, and reference) near the cantilever provides many advantages, such as the usage of conventional AFM fluid cells also for SECM or enables the measurement in liquid drops. Moreover, the other electrodes become easily exchangeable as they are combined with the cantilever substrate. Thereby, the handling is improved significantly. We demonstrated that high-resolution SECM, i.e., resolving features smaller than 250 nm in the electrochemical signal, could be achieved with the new setup and that the electrochemical performance was equivalent to the one obtained with macroscopic electrodes. Full article

Myocardial fibrosis progression and imbalanced redox state are closely associated with increased extracellular matrix (ECM) stiffness. Candesartan (CAN), an angiotensin II (Ang II) receptor inhibitor, has shown promising anti-fibrosis and antioxidant efficacy in previous cardiovascular disease studies. However, the effect of ECM stiffness on CAN efficacy remains elusive. In this study, we constructed rat models with three different degrees of myocardial fibrosis and treated them with CAN, and then characterized the stiffness, cardiac function, and NADPH oxidase-2 (NOX2) expression of the myocardial tissues. Based on the obtained stiffness of myocardial tissues, we used polyacrylamide (PA) gels with three different stiffness to mimic the ECM stiffness of cardiac fibroblasts (CFs) at the early, middle, and late stages of myocardial fibrosis as the cell culture substrates and then constructed CFs mechanical microenvironment models. We studied the effects of PA gel stiffness on the migration, proliferation, and activation of CFs without and with CAN treatment, and characterized the reactive oxygen species (ROS) and glutathione (GSH) levels of CFs using fluorometry and scanning electrochemical microscopy (SECM). We found that CAN has the best amelioration efficacy in the cardiac function and NOX2 levels in rats with medium-stiffness myocardial tissue, and the most obvious anti-fibrosis and antioxidant efficacy in CFs on the medium-stiffness PA gels. Our work proves the effect of ECM stiffness on CAN efficacy in myocardial anti-fibrosis and antioxidants for the first time, and the results demonstrate that the effect of ECM stiffness on drug efficacy should also be considered in the treatment of cardiovascular diseases. Full article

Monitoring pH changes at the micro/nano scale is essential to gain a fundamental understanding of surface processes. Detection of local pH changes at the electrode/electrolyte interface can be achieved through the use of micro-/nano-sized pH sensors. When combined with scanning electrochemical microscopy (SECM), these sensors can provide measurements with high spatial resolution. This article reviews the state-of-the-art design and fabrication of micro-/nano-sized pH sensors, as well as their applications based on SECM. Considerations for selecting sensing probes for use in biological studies, corrosion science, in energy applications, and for environmental research are examined. Different types of pH sensitive probes are summarized and compared. Finally, future trends and emerging applications of micro-/nano-sized pH sensors are discussed. Full article

The corrosion behavior and mechanism of 13Cr stainless steel in the solution with 1 mol/L NaCl and 5 mmol/L KI were investigated by weight loss method, scanning electrochemical microscopy (SECM), the phase analysis (XRD) of inclusions, and surface analysis technique (SEM and EDS). Results showed that the corrosion rate was a linear relationship with the time and Cl⁻ concentration. The corrosion became serious with the increase in time and Cl⁻ concentration. The corrosion occurred in the unstable electroactive points that contained aluminum oxide and metallic phase inclusions. The generation and disappearance of the electroactive points simultaneously occurred with the corrosion. The active dissolved level on different areas of the surface of 13Cr stainless-steel sample was different. The oxidation current peak of the sample presented the strip shape. The corrosion dissolution was mainly caused by aluminum oxide inclusions (Al₂O₃) and FeAl phase. Full article

In the present work, the localized electrochemical behavior of redox molecule in ionic liquid has been investigated using scanning electrochemical microscopy. The electrochemical response of ferrocenyl-imidazolium redox mediator was studied by recording approach curves over a conducting and insulating substrate in an undiluted ionic liquid. The SECM approach curve over the conducting substrate displays a positive feedback, as observed in classical solvent. However, in the case of the insulating substrate, the approach curve reveals different shapes, depending on the used approach speed. In this configuration, low approach speed is necessary to reach the expected negative feedback. Interestingly, at a very close distance between the UME and the insulating substrate, a thin film behavior is revealed. In addition, the approach curves on both insulator and conducting substrates can be reconstructed from punctual responses at different distance tip-substrate. The latter match perfectly with the expected theoretical curves over conducting and insulating under diffusion control. Full article

Scanning Electrochemical Microscopy (SECM) is increasingly used in the study and characterization of thin surface films as well as organic and inorganic coatings applied on metals for the collection of spatially- and chemically-resolved information on the localized reactions related to material degradation processes. The movement of a microelectrode (ME) in close proximity to the interface under study allows the application of various experimental procedures that can be classified into amperometric and potentiometric operations depending on either sensing faradaic currents or concentration distributions resulting from the corrosion process. Quantitative analysis can be performed using the ME signal, thus revealing different sample properties and/or the influence of the environment and experimental variables that can be observed on different length scales. In this way, identification of the earlier stages for localized corrosion initiation, the adsorption and formation of inhibitor layers, monitoring of water and specific ions uptake by intact polymeric coatings applied on metals for corrosion protection as well as lixiviation, and detection of coating swelling—which constitutes the earlier stages of blistering—have been successfully achieved. Unfortunately, despite these successful applications of SECM for the characterization of surface layers and coating systems applied on metallic materials, we often find in the scientific literature insufficient or even inadequate description of experimental conditions related to the reliability and reproducibility of SECM data for validation. This review focuses specifically on these features as a continuation of a previous review describing the applications of SECM in this field. 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

Spatially resolved information on corrosion reactions operating at the cut edges of coated metals can be obtained using microelectrochemical scanning techniques using a suitable selection of operation modes and scanning probes. The scanning vibrating electrode technique (SVET) provides current density maps with a spatial resolution of the order of the dimensions of the sample, which allows the temporal evolution of the corrosion reactions to be followed over time. This leads to the identification and localization of cathodic and anodic sites, although the technique lacks chemical specificity for the unequivocal identification of the reactive species. The application of scanning electrochemical microscopy (SECM) was previously limited to image cathodic reaction sites, either due to oxygen consumption in the amperometric operation or by the alkalinisation of the electrolyte in potentiometric operation. However, it is shown that anodic sites can be effectively monitored using an ion-selective microelectrode (ISME) as a probe. The ISME probes detected differences in the local concentrations of Zn²⁺ and OH⁻ ions from the cut edges of a complete coil coating system compared to the same system after the polymeric layers were removed. In this way, it has been shown that the inhibitor loading in the polymer layers effectively contributes to reducing the corrosion rates at the cut edge, thus helping to extend the useful life of the sacrificial galvanized layer bonded directly to the steel matrix. Additionally, these two probe configurations can be integrated into a multi-electrode tip for potentiometric operation to simultaneously monitor localized changes in pH values and metal ion dissolution in a single scan. Spatial and temporal distributions were further investigated using different rastering procedures, and the potential of constructing pseudomaps for 2D-imaging is described. Full article