Multi-principal element alloys (MPEAs) are gaining interest in corrosion and electrocatalysis research due to their electrochemical stability across a broad pH range and the design flexibility they offer. Using the equimolar CrCoNi alloy, we observe significant metal dissolution in a corrosive electrolyte (0.1 M NaCl, pH 2) concurrently with the oxygen evolution reaction (OER) in the transpassive region, despite the absence of hysteresis in polarization curves or other obvious corrosion indicators. We present a characterization scheme to delineate the contribution of OER and alloy dissolution, using scanning electrochemical microscopy (SECM) for OER-onset detection, and quantitative chemical analysis with inductively coupled-mass spectrometry (ICP-MS) and ultraviolet visible light (UV/Vis) spectrometry to elucidate metal dissolution processes. In situ electrochemical atomic force microscopy (EC-AFM) revealed that the transpassive metal dissolution on CrCoNi is dominated by intergranular corrosion. These results have significant implications for the stability of MPEAs in corrosion systems, emphasizing the necessity of analytically determining metal ions released from MPEA electrodes into the electrolyte when evaluating Faradaic efficiencies of OER catalysts. The release of transition metal ions not only reduces the Faradaic efficiency of electrolyzers but may also cause poisoning and degradation of membranes in electrochemical reactors.

Heterogeneous nature is a pivotal aspect of cancer, rendering treatment problematic and frequently resulting in recurrence. Therefore, advanced techniques for identifying subpopulations of a tumour in an intact state are essential to develop novel screening platforms that can reveal differences in treatment response among subpopulations. Herein, we conducted a non-invasive analysis of oxygen metabolism on multiple subpopulations of patient-derived organoids, examining its potential utility for non-destructive identification of subpopulations. We utilised scanning electrochemical microscopy (SECM) for non-invasive analysis of oxygen metabolism. As models of tumours with heterogeneous subpopulations, we used patient-derived cancer organoids with a distinct growth potential established using the cancer tissue-originated spheroid methodology. Scanning electrochemical microscopy measurements enabled the analysis of the oxygen consumption rate (OCR) for individual organoids as small as 100 µm in diameter and could detect the heterogeneity amongst studied subpopulations, which was not observed in conventional colorectal cancer cell lines. Furthermore, our oxygen metabolism analysis of pre-isolated subpopulations with a slow growth potential revealed that oxygen consumption rate may reflect differences in the growth rate of organoids. Although the proposed technique currently lacks single-cell level sensitivity, the variability of oxygen metabolism across tumour subpopulations is expected to serve as an important indicator for the discrimination of tumour subpopulations and construction of novel drug screening platforms in the future.

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.

We report quantitative determination of extracellular H2O2 released from single COS-7 cells with high spatial resolution, using scanning electrochemical microscopy (SECM). Our strategy of depth scan imaging in vertical x-z plane was conveniently utilized to a single cell for obtaining probe approach curves (PACs) to any positions on the membrane of a live cell by simply drawing a vertical line on one depth SECM image. This SECM mode provides an efficient way to record a batch of PACs, and visualize cell topography simultaneously. The H2O2 concentration at the membrane surface in the center of an intact COS-7 cell was deconvoluted from apparent O2, and determined to be 0.020 mM by overlapping the experimental PAC with the simulated one having a known H2O2 release value. The H2O2 profile determined in this way gives insight into physiological activity of single live cells. In addition, intracellular H2O2 profile was demonstrated using confocal microscopy by labelling the cells with a luminomphore, 2\',7\'-dichlorodihydrofluorescein diacetate. The two methodologies have illustrated complementary experimental results of H2O2 detection, indicating that H2O2 generation is centered at endoplasmic reticula.

Conducting polymers show attractive characteristics as electrode materials for micro-electrochemical energy storage (MEES). However, there is a lack of characterization techniques to study conjugated/conducting polymer-based nanostructured electrodes. Here, scanning electrochemical microscopy (SECM) is introduced as a new technique for in situ characterization and acceleration of degradation processes of conducting polymers. Electrodes of PEDOT:PSS on flat silicon, silicon nanowires (SiNWs) and silicon nanotrees (SiNTrs) are analyzed by SECM in feedback mode with approach curves and chronoamperometry. The innovative degradation method using SECM reduces the time required to locally degrade polymer samples to a few thousand seconds, which is significantly shorter than the time usually required for such studies. The degradation rate is modeled using Comsol Multiphysics. The model provides an understanding of the phenomena that occur during degradation of the polymer electrode and describes them using a mathematical constant A0 and a time constant τ.

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.

Development of ultramicroelectrodes and nanoelectrodes opened interesting possibilities in the investigation electron transfer phenomena, including their application as probe electrodes in scanning electrochemical microscopy (SECM). Analytical prowess of SECM was often shadowed by long operation times required for analysis of a wide sample area. In this report, we developed a multi-channel nanoelectrode bundle for simultaneous electroanalysis of multiple orthogonal redox reactions in one bath. Four nanoelectrodes of diameters 100-400 nm were shown to be bundled in a 2 μm disk area. The nanoelectrode assembly was implemented as a tip electrode for multi-channel SECM, dramatically improving the time efficiency of SECM operations. The nanoelectrode bundle was also demonstrated as a stand-alone microprobe for electroanalytical investigations in small volumes such as ceramic confinements and biologically important compartments. The development reported in this work should benefit electrochemical analyses of various systems, especially those involving SECM and fine spatial control.

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.

Because of their high specific capacity and rather low operating potential, silicon-based negative electrode materials for lithium-ion batteries have been the subject of extensive research over the past 2 decades. Although the understanding of the (de)lithiation behavior of silicon has significantly increased, several major challenges have not been solved yet, hindering its broad commercial application. One major issue is the low initial Coulombic efficiency and the ever-present self-discharge of silicon electrodes. Self-discharge itself affects the long-term stability of electrochemical storage systems and, additionally, must be taken into consideration for inevitable prelithiation approaches. The impact of the crystalline Li15Si4 phase is of great interest as the phase transformation between crystalline (c) and amorphous (a) phases not only increases the specific surface area but also causes huge polarization. Moreover, there is the possibility for electrochemical over-lithiation toward the Li15+aSi4 phase because of the electron-deficient Li15Si4 phase, which can be highly reactive toward the electrolyte. This poses the question about the impact of the c-Li15Si4 phase on the self-discharge behavior in comparison to its amorphous counterpart. Here, silicon thin films used as model electrodes are lithiated to cut-off potentials of 10 mV and 50 mV versus Li|Li+ (U10mV and U50mV) in order to systematically investigate their self-discharge mechanism via open-circuit potential (UOCP) measurements and to visualize the solid electrolyte interphase (SEI) growth by means of scanning electrochemical microscopy. We show that the c-Li15Si4 phase is formed for the U10mV electrode, while it is not found for the U50mV electrode. In turn, the U50mV electrode displays an almost linear self-discharge behavior, whereas the U10mV electrode reaches a UOCP plateau at ca. 380 mV versus Li|Li+, which is due to the phase transition from c-Li15Si4 to the a-LixSi phase. At this plateau potential, the phase transformation at the Si|electrolyte interface results in an electronically more insulating and more uniform SEI (U10mV electrode), while the U50mV electrode displays a less uniform SEI layer. In summary, the self-discharge mechanism of silicon electrodes and, hence, the irreversible decomposition of the electrolyte and the corresponding SEI formation process heavily depend on the structural nature of the underlying lithium-silicon phase.

Herein we report the use of scanning electrochemical microscopy (SECM) together with electrochemical and spectroscopic techniques to develop and characterise a stable and uniformly reactive chemically modified platinum electrode for NADH electrocatalysis. In order to achieve this, a range of different approaches for thionine entrapment within an electropolymerised poly (3,4-ethylendioxythiophene) (PEDOT) film were evaluated using SECM imaging in the presence of NADH, demonstrating the uniformity of the reactive layer towards NADH oxidation. The effect of electrolyte type and time scale employed during PEDOT electropolymerisation was examined with respect to thionine loading and the resulting charge transport diffusion coefficient (DCT) estimated via chronoamperometry. These studies indicated a decrease in DCT as thionine loading increased within the PEDOT film, suggesting that charge transport was diffusion limited within the film. Additionally, thionine functionalised nanotubes were formed, providing a stable support for lactate dehydrogenase entrapment while lowering the rate of thionine leaching, determined via SECM imaging. This enabled lactate determination at Eapp = 0.0 V vs Ag/AgCl over the range 0.25-5 mM in the presence of 1 mM NAD+.