Scanning Electrochemical Microscopy Research Articles

Solution-processed asymmetry conjugated reticular oligomers for large-area panel photoelectrodes in photoelectrochemical devices

Covalent organic frameworks (COFs) show potential in photoelectrochemical (PEC) water reduction. Herein, we synthesize solution-processed benzoxazole-based conjugated reticular oligomers (BBO-CROs) in micelle nanoreactors, acting as an “electronic paint” for fabricating consecutive panel-type photoelectrodes for PEC water reduction. The small-molecule BBO-CROPDA, BBO-CRODHTA, and BBO-CROBPY exhibit a narrower energy bandgap and prolong the fluorescence lifetimes of photoinduced charge carriers compared to bulk BBO-COFs. Colloidal COFs in PEC water reduction are illustrated through the creation of flexible full devices via spinning coating. The optimized photoelectrode CuI/BBO-CROBPY+P27/SnO2/Pt result in ΔJ of 86.5 μA cm−2 at 0.4 V vs. RHE, which is 86.5 times higher than that of bulk BBO-COFBPY. The CuI/BBO-CROBPY+P27/SnO2/Pt photoelectrode with an area of 100 cm² displays an impressive ΔJ of 82.0 μA cm−2 with good durability. A flat photoelectrode surface and the generation of photogenerated charge carriers under light are observed using scanning electrochemical microscopy (SECM) as an in-situ technique. Density Functional Theory (DFT) calculation indicates that the asymmetry of the BBO unit prompts electrons to preferentially move in a defined direction upon light excitation in the small-molecular framework, thereby suppressing electron backflow. This work overcomes COF processability limitations in PEC water reduction and paves the way for using flexible devices.

Pulse Electrolysis Turns on CO2 Methanation through N‐Confused Cupric Porphyrin

AbstractBreaking the D4h symmetry in the square‐planar M−N4 configuration of macrocycle molecular catalysts has witnessed enhanced electrocatalytic activity, but at the expense of electrochemical stability. Herein, we hypothesize that the lability of the active Cu−N3 motifs in the N‐confused copper (II) tetraphenylporphyrin (CuNCP) could be overcome by applying pulsed potential electrolysis (PPE) during electrocatalytic carbon dioxide reduction. We find that applying PPE can indeed enhance the CH4 selectivity on CuNCP by 3 folds to reach the partial current density of 170 mA cm−2 at >60 % Faradaic efficiency (FE) in flow cell. However, combined ex situ X‐ray diffraction (XRD), transmission electron microscope (TEM), and in situ X‐ray absorption spectroscopy (XAS), infrared (IR), Raman, scanning electrochemical microscopy (SECM) characterizations reveal that, in a prolonged time scale, the decomplexation of CuNCP is unavoidable, and the promoted water dissociation under high anodic bias with lowered pH and enriched protons facilitates successive hydrogenation of *CO on the irreversibly reduced Cu nanoparticles, leading to the improved CH4 selectivity. As a key note, this study signifies the adaption of electrolytic protocol to the catalyst structure for tailoring local chemical environment towards efficient CO2 reduction.

Pulse Electrolysis Turns on CO2 Methanation through N-Confused Cupric Porphyrin.

Breaking the D4h symmetry in the square-planar M-N4 configuration of macrocycle molecular catalysts has witnessed enhanced electrocatalytic activity, but at the expense of electrochemical stability. Herein, we hypothesize that the lability of the active Cu-N3 motifs in the N-confused copper (II) tetraphenylporphyrin (CuNCP) could be overcome by applying pulsed potential electrolysis (PPE) during electrocatalytic carbon dioxide reduction. We find that applying PPE can indeed enhance the CH4 selectivity on CuNCP by 3 folds to reach the partial current density of 170 mA cm-2 at >60 % Faradaic efficiency (FE) in flow cell. However, combined ex situ X-ray diffraction (XRD), transmission electron microscope (TEM), and in situ X-ray absorption spectroscopy (XAS), infrared (IR), Raman, scanning electrochemical microscopy (SECM) characterizations reveal that, in a prolonged time scale, the decomplexation of CuNCP is unavoidable, and the promoted water dissociation under high anodic bias with lowered pH and enriched protons facilitates successive hydrogenation of *CO on the irreversibly reduced Cu nanoparticles, leading to the improved CH4 selectivity. As a key note, this study signifies the adaption of electrolytic protocol to the catalyst structure for tailoring local chemical environment towards efficient CO2 reduction.

Study of gold electrodissolution by scanning electrochemical microscopy in different modes

The electrodissolution of gold has already been widely studied by several methods, but no consensus concerning the reaction mechanism has been reached. In this work, the scanning electrochemical microscopy (SECM) has been used in transient condition for studying the electrodissolution of gold in H2SO4 solutions, with different concentration of chloride added, in order to elucidate the elementary steps of this mechanism. The electroactive species generated during Au dissolution, namely AuCl2−, AuCl3− and AuCl4−, were detected using a Pt microelectrode positioned at various distances from the Au electrode. Additionally, the SECM in transient mode (AC-SECM), which allows several transfer functions to be determined, has been used to characterize the presence and the relaxation time-constants of adsorbed intermediates formed at the Au electrode during its dissolution. The interpretation of the results is presented and discussed according to the different mechanisms reported in the literature, and subsequently, a new reaction mechanism is proposed.

In-situ pH monitoring of pre-notched X80 pipeline steel using an all-solid-state Pt/RuOx ultra-micro pH sensor

In the notch microenvironment caused by the stress corrosion of pipeline steel, the local pH value changes mediated by anodic-cathodic corrosion reactions played an important role in comprehending the local corrosion behavior. To address this issue, a radius 5 µm all-solid-state Pt/RuOx ultra-micro pH sensor was developed using cyclic voltammetry deposition method, which was combined with scanning electrochemical microscopy (SECM) to achieve in-situ monitoring the local pH distribution and evolution of the pre-notched X80 pipeline steel. The micro-sensor demonstrates a near Nernstian slope of −60.0 ± 3 mV/pH within the pH value range of 2.00–12.00, accompanied by an exceptionally rapid response time of 200 ms. Moreover, it exhibits high accuracy, strong long-term monitoring ability and remarkable resistance to the interference of common ions in seawater and ferrous ions generated by the corrosion of pipeline steel. Through monitoring the local pH distribution in simulated seawater solution at the notch of X80 pipeline steel, it was found that obvious pH alkalization occurs first on both the surface and inside of the notch, followed by gradual acidification, and this phenomenon is more obvious at the front of the notch. Combined with other characterization methods, a possible corrosion reaction mechanism at the notch of stress corrosion was proposed.

Au Micro‐ and Nanoelectrodes as Local Voltammetric pH Sensors During Oxygen Evolution at Electrocatalyst‐Modified Electrodes

The scarcity of state‐of‐the‐art oxygen evolution reaction (OER) electrocatalysts has led to intensive research on alternative viable electrocatalytic materials. While activity and cost are the main factors to be sought after, the catalyst stability under harsh acidic conditions is equally crucial. Considering that OER is a proton‐coupled electron‐transfer reaction that involves local acidification of the reaction environment by liberation of H+, the catalyst stability can be largely compromised in such conditions. Consequently, probing the pH value near the catalyst surface under operation leads to a deeper understanding of this process. The applicability of bare Au microelectrodes and nanoelectrodes as sensitive local pH probes during OER is shown in this work by using scanning electrochemical microscopy (SECM). Two case studies are presented, including the state‐of‐the‐art OER catalyst (IrO2) in acidic media and a ZnGa2O4 catalyst in alkaline buffered solution, demonstrating the suitability of the Au probe to accurately determine the local pH value in a wide pH range.

Porous membranes integrated into electrochemical systems for bioanalysis

AbstractPorous membranes have emerged as promising platforms for bioanalysis because of their unique properties including high surface area, selective permeability, and compatibility with electrochemical techniques. This minireview presents an overview of the development and applications of porous membrane‐based electrochemical systems for bioanalysis. First, we discuss the existing fabrication methods for porous membranes. Next, we summarize electrochemical detection strategies for bioanalysis using porous membranes. Electrochemical biosensors and cell chips fabricated from porous membranes are discussed as well. Furthermore, porous micro‐/nanoneedle devices for bioapplications are described. Finally, the utilization of scanning electrochemical microscopy for cell analysis on porous membranes and electrochemiluminescence sensors is demonstrated. Future perspectives of the described membrane detection strategies and devices are outlined in each section. This work can help enhance the performance of porous membrane‐based electrochemical systems and expand the range of their potential applications.

Revealing the Heterogeneous Bubble Nucleation at Individual Silica Nanoparticles.

Deep understanding of the bubble nucleation process is universally important in systems, from chemical engineering to materials. However, due to its nanoscale and transient nature, effective probing of nucleation behavior with a high spatiotemporal resolution is prohibitively challenging. We previously reported the measurement of a single nanobubble nucleation at a nanoparticle using scanning electrochemical cell microscopy, where the bubble nucleation and formation were inferred from the voltammetric responses. Here, we continue the study of heterogeneous bubble nucleation at interfaces by regulating the local nanostructures using silica nanoparticles with a distinct surface morphology. It is demonstrated that, compared to the smooth spherical silica nanoparticles, the raspberry-like nanoparticles can further significantly reduce the nucleation energy barrier, with a critical peak current about 23% of the bare carbon surfaces. This study advances our understanding of how surface nanostructures direct the heterogeneous nucleation process and may offer a new strategy for surface engineering in gas involved energy conversion systems.

Redox-active green-electrode: Plant-extract based rutin and caffeic acid functionalized MWCNT for scanning electrochemical microscopy imaging and selective electrocatalytic oxidative sensing of dopamine

A straightforward, environmentally friendly, and rapid in-situ electrochemical functionalization of Rutin (Rut) and Caffeic acid (Caf) on a multiwalled carbon nanotube-modified glassy carbon electrode, denoted as GCE/MWCNT@Herb-Redox (Herb-Redox =redox active species from the plant extract), has been demonstrated. This method utilizes an eco-friendly, plant-based water extract from Indian Borage (Coleus amboinicus), referred to as IBE, as a precursor sample. The as-prepared molecular bio-electrode showed a well-defined and stable surface-confined redox response at standard electrode potentials, Eo’ = 0.160 and 0.200 V vs Ag/AgCl in pH 7 phosphate buffer solution. By performing physicochemical and molecular characterisations using TEM, SEM, UV–Vis, FTIR, high-performance thin-layer chromatographic techniques, it has been confirmed that Rut and Caf from the Herbal-plant were selectively immobilized on the MWCNT-modified electrode. Using scanning electrochemical microscopy (SECM), the electroactive sites of the molecular-electrode were mapped. The electrocatalytic function of the GCE/MWCNT@Herb-Redox was demonstrated by performing a dopamine (DA) oxidation reaction as a model system in pH 7 PBS using CV and amp-it techniques. The results showed 100—10,000 times increase in the DA- oxidation current response over the values quoted with many of the literature reports highlighting the efficient functionality of the new molecular electrocatalytic system. As a proof of concept, batch injection analysis based elegant dopamine sensing using screen-printed electrode/MWCNT@Herb-Redox as an electrochemical detector has been demonstrated and there is no biochemical interference was observed. Since the electrochemical approach follows a green chemistry route for the modification, this bioelectrode showed a new platform for eco-friendly electrocatalytic applications.

Corrosion Investigation by Scanning Electrochemical Microscopy of AISI 446 and Ti-Coated AISI 446 Ferritic Stainless Steel as Potential Material for Bipolar Plate in PEMWE

AbstractThe components of proton exchange membrane water electrolysers frequently experience corrosion issues, especially at high anodic polarization, that restrict the use of more affordable alternatives to titanium. Here, we investigate localized corrosion processes of bare and Ti-coated AISI 446 ferritic stainless steel under anodic polarization by scanning electrochemical microscopy (SECM) in sodium sulphate and potassium chloride solutions. SECM approach curves and area scans measured at open-circuit potential (OCP) of the samples in the feedback mode using a redox mediator evidence a negative feedback effect caused by the surface passive film. For the anodic polarization of the sample, the substrate generation-tip collection mode enables to observe local generation of iron (II) ions, as well as formation of molecular oxygen. For the uncoated AISI 446 sample, localized corrosion is detected in sodium sulphate solution simultaneously with oxygen formation at anodic potentials of 1.0 V vs. Ag/AgCl, whereas significant pitting corrosion is observed even at 0.2 V vs. Ag/AgCl in potassium chloride solution. The Ti-coated AISI 446 sample reveals enhanced corrosion resistance in both test solutions, without any evidence of iron (II) ions generation at anodic potentials of 1.2 V vs. Ag/AgCl, where only oxygen formation is observed.

Determining kinetics of electrochemical carbon dioxide reduction to carbon monoxide with scanning electrochemical microscopy

This study reports on determining kinetics of electrochemical reduction CO2 to CO on Au catalysts using the substrate generation/tip collection (SG/TC) mode of scanning electrochemical microscopy (SECM). We introduced a simple but effective method based on transient technique to obtain a series of apparent heterogeneous rate constants k based on Fick’s second law by controlling the tip-substrate distance and the voltage of the substrate electrode within the SECM framework. By analysis the transient current recorded during the chronoamperometric characterization, we can successfully determine the apparent rate constant k for the simplified total conversion process of CO2 + 2H+ + 2e- → CO + H2O onto Au catalyst electrode serving as an example, which increases from 5.02 × 10–2 cm⋅s−1 to 7.16 × 10–2 cm⋅s−1 in the low potential range of −2.2 to −2.6 V (vs. Pt/PPy) and decreases to 6.54 × 10-2 cm⋅s−1 at –2.8 V (vs. Pt/PPy). The method proposed here can be applied to quantitatively analyze the kinetic of CO2 electrochemical reduction reaction, and thus provide a useful tool to guide the synthesis of catalyst as well as in-situ performance evaluation.

Simultaneous Scanning Ion Conductance and Electrochemical Microscopy in Lithium‐Ion Battery Research

AbstractDeeper understanding of processes involved in operation of lithium‐ion batteries (LIBs) is necessary to further optimize them for future applications. Extensive research was conducted on the formation of a solid electrolyte interphase (SEI) on negative battery electrodes, still leaving several questions unanswered. Scanning probe microscopies (SPMs) enable in situ and operando investigations and have the potential to explain some phenomena. Scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM) could be employed in LIB studies. A novel SICM method based on the redox couple ferrocene/ferrocenium is introduced for applications in carbonate solvents widely used in LIBs. Proof of concept measurements were conducted with a micro milled copper circuit board as model substrate. Furthermore, the proposed SICM approach was hyphenated with feedback mode SECM resulting in the simultaneous mapping of morphology and electrochemical activity. A flexible dual‐probe arrangement was developed enabling usage of both SPM techniques at the same time, and furthermore, an easy replacement of both individual probes if needed. The setup was applied in the characterisation of commercial graphite electrodes for LIBs before and after conducting a pre‐charging protocol. Changes in electrochemical activity and topography of the graphite electrode were resolved in simultaneously generated SECM/SICM recordings.

Unravelling microstructure-electroactivity relationships in free-standing polycrystalline boron-doped diamond: A mapping study

In this work, four different techniques were concurrently applied to study the interplay between local electroactivity and electrode surface characteristics of free-standing, polycrystalline boron-doped diamond (BDD). Scanning electron microscopy, electron back-scatter diffraction, Raman mapping and scanning electrochemical microscopy were used to probe the electrode morphology, grain orientation and boundaries, composition, and local electrochemical activity, respectively. Both nucleation and growth BDD surfaces together with the cross-section area were carefully investigated for the first time in a single study using the combination of all four techniques. This enabled us to obtain significant insights into the highly heterogeneous nature of the polycrystalline BDD material. Notably, boron dopants were confirmed to be non-uniformly distributed over the BDD material, which is characterized by a distinct columnar structure and composition of grains of various orientations. Particularly, the highest electrochemical activity was recorded on the highest doped (111) crystal orientation. In contrast, the averagely boron-doped (100)-oriented facet showed non-conductive nature. This highlights that the local electrochemical activity of the BDD surface is strongly grain-dependent and the most significant factors governing the obtained responses are crystallographic orientation and boron doping. Moreover, increased boron and sp2 carbon content in the boundary regions was recognized by Raman mapping. However, such localized enrichment in impurities did not translate into enhanced electrochemical activity, which implies that boron atoms at the inter-grain areas are predominantly inactive. Finally, it is crucial to consider all characteristics of the polycrystalline BDD including crystal orientation, which is particularly relevant if micro- and nanoscale probing is intended.

Multifunctional graphitic carbon nitride/manganese dioxide/epoxy nanocomposite coating on steel for enhanced anticorrosion, flame retardant, mechanical, and hydrophobic properties

Benzidine (Bz) was used to modify the nanofiller, manganese dioxide (MnO2), and the resulting Bz/MnO2 was then encased in pure epoxy resin (EP) with graphitic carbon nitride (GCN). The effectiveness of epoxy-coated mild steel in protecting against varying concentrations of GCN/Bz-MnO2 was assessed through the use of electrochemical techniques in natural seawater. The flame retardancy capabilities of the epoxy coating were significantly improved by the incorporation of GCN/Bz-MnO2. The EP-GCN-Bz/MnO2 nanocomposites display peak heat release rate (PHRR) and total heat release (THR) values which are 79 % and 62 % lesser than that of pure EP, respectively. When compared to a pure epoxy coating, the results of salt spray tests indicated that the addition of GCN/Bz-MnO2 improved corrosion protection and decreased water absorption. Electrochemical impedance spectroscopy (EIS) studies showed that the epoxy-GCN/Bz-MnO2 coating still had an improved resistance of 6.40E10 Ω.cm2 even after 30 days of exposure to seawater. Scanning electrochemical microscopy (SECM) displayed lowest ferrous ion dissipation (1.0 I/nA) in the EP-GCN/Bz-MnO2 nanocomposite coated steel. Potentiodynamic polarization testing showed that EP-GCN-Bz/MnO2 had a lower current density (icorr: 0.03 µA/cm2) in comparison with other coatings. This is mainly because the Bz alteration of the MnO2 nanoparticles and their successful coordination with GCN sheets result in a noticeably more compact nanostructure that lowers aggregation and increases binding capacity. Surface-modified GCN was found to be improved in its breakdown products, leading to the production of a strong, inert nanolayered covering, according to Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) analysis. Water contact angle (WCA) of 160° demonstrates the exceptional water resistance of the recently developed EP-GCN/Bz-MnO2 coating. In terms of hardness and adhesion strength, Bz/MnO2 wrapped in GCN had good mechanical characteristics on the epoxy substrate. The improved adhesive strength (18.3 MPa) for mild steel coated with EP-GCN/Bz-MnO2 was attained prior to being immersed in seawater. The EP-GCN/Bz-MnO2 crystallizes form a robust, inert coating that prevents ions from accessing the specimen. The coating has increased adhesive strength as a result, and it can withstand deep immersions without losing its integrity. Hence, the EP-GCN/Bz-MnO2 nanocomposite might work as a useful coating component in the automotive industry.

Investigating the Role of Extracellular Matrix Stiffness in Modulating the Ferroptosis Process in Hepatocellular Carcinoma Cells via Scanning Electrochemical Microscopy.

Extracellular matrix (ECM) stiffness modulates a variety of cellular processes, including ferroptosis, a process with significant potential implications for hepatocellular carcinoma (HCC) fibrosis and cirrhosis. However, the exact relationship between ECM stiffness and HCC ferroptosis is yet unclarified, partially due to the lack of in situ information on key parameters of the ferroptosis process of living HCC cells. This study pioneers the use of in vitro mechanical microenvironment models of HCC and the scanning electrochemical microscopy (SECM) technique for understanding this interplay. We first cultured HuH7 cells on 4.0, 18.0, and 44.0 kPa polyacrylamide (PA) gels to simulate early, intermediate, and advanced HCC ECM stiffness, respectively. Then, we used SECM to in situ monitor changes in cell membrane permeability, respiratory activity, and reactive oxygen species (ROS) levels of erastin-induced HuH7 cells on PA gels, finding that increasing ECM stiffness potentiates ferroptosis, including increased membrane permeabilization and H2O2 release as well as reduced respiratory activity. Through further transcriptome sequencing and molecular biology measurements, we identified a critical role for focal adhesion kinase (FAK)-mediated yes-associated protein (YAP) in regulating the ferroptosis process dependent on ECM stiffness, which provides novel insights into the mechanical regulation of ferroptosis in HCC cells and may pave the way for innovative therapeutic strategies.

Scanning electrochemical probe microscopy: towards the characterization of micro- and nanostructured photocatalytic materials.

Platinum-black (Pt-B) has been demonstrated to be an excellent electrocatalytic material for the electrochemical oxidation of hydrogen peroxide (H2O2). As Pt-B films can be deposited electrochemically, micro- and nano-sized conductive transducers can be modified with Pt-B. Here, we present the potential of Pt-B micro- and sub-micro-sized sensors for the detection and quantification of hydrogen (H2) in solution. Using these microsensors, no sampling step for H2 determination is required and e.g., in photocatalysis, the onset of H2 evolution can be monitored in situ. We present Pt-B-based H2 micro- and sub-micro-sized sensors based on different electrochemical transducers such as microelectrodes and atomic force microscopy (AFM)-scanning electrochemical microscopy (SECM) probes, which enable local measurements e.g., at heterogenized photocatalytically active samples. The microsensors are characterized in terms of limits of detection (LOD), which ranges from 4.0 μM to 30 μM depending on the size of the sensors and the experimental conditions such as type of electrolyte and pH. The sensors were tested for the in situ H2 evolution by light-driven water-splitting, i.e., using ascorbic acid or triethanolamine solutions, showing a wide linear concentration range, good reproducibility, and high sensitivity. Proof-of-principle experiments using Pt-B-modified cantilever-based sensors were performed using a model sample platinum substrate to map the electrochemical H2 evolution along with the topography using AFM-SECM.

Effects of media composition and light exposure on the electrochemical current response during scanning electrochemical microscopy live cell imaging.

Scanning Electrochemical Microscopy (SECM) has been used as a non-invasive electrochemical technique for studying cellular processes. SECM enables the quantification of cellular metabolites in real-time providing a deeper understanding of cellular responses to external stimuli. SECM imaging of living cells requires maintaining an ideal physiological environment to ensure reliable data collection on cellular reactivity. The cellular response can be directly influenced by physicochemical parameters including cell media composition, temperature and light exposure. This research demonstrates the effect of media composition on the electrochemical current signal of adenocarcinoma cervical cancer (HeLa) cells during SECM measurements using ferrocenemethanol as a redox mediator. Investigated media that are commonly used as electrolyte, are phosphate buffered saline (PBS), and Dulbecco's modified Eagle's medium (DMEM) in the absence and presence of fetal bovine serum (FBS). In addition, this research demonstrates that fluctuating light illumination impacts the stability of the cellular electrochemical current response. Our findings reveal that media composition and illumination are important parameters that must be carefully considered and monitored during SECM live cell imaging.

Transient theory for scanning electrochemical microscopy of biological membrane transport: uncovering membrane-permeant interactions.

Scanning electrochemical microscopy (SECM) has emerged as a powerful method to quantitatively investigate the transport of molecules and ions across various biological membranes as represented by living cells. Advantageously, SECM allows for the in situ and non-destructive imaging and measurement of high membrane permeability under simple steady-state conditions, thereby facilitating quantitative data analysis. The SECM method, however, has not provided any information about the interactions of a transported species, i.e., a permeant, with a membrane through its components, e.g., lipids, channels, and carriers. Herein, we propose theoretically that SECM enables the quantitative investigation of membrane-permeant interactions by employing transient conditions. Specifically, we model the membrane-permeant interactions based on a Langmuir-type isotherm to define the strength and kinetics of the interactions as well as the concentration of interaction sites. Finite element simulation predicts that each of the three parameters uniquely affects the chronoamperometric current response of an SECM tip to a permeant. Significantly, this prediction implies that all three parameters are determinable from an experimental chronoamperometric response of the SECM tip. Complimentarily, the steady-state current response of the SECM tip yields the overall membrane permeability based on the combination of the three parameters. Interestingly, our simulation also reveals the optimum strength of membrane-permeant interactions to maximize the transient flux of the permeant from the membrane to the tip.

Matrix stiffness-dependent microglia activation in response to inflammatory cues: in situ investigation by scanning electrochemical microscopy.

Microglia play a crucial role in maintaining the homeostasis of the central nervous system (CNS) by sensing and responding to mechanical and inflammatory cues in their microenvironment. However, the interplay between mechanical and inflammatory cues in regulating microglia activation remains elusive. In this work, we constructed in vitro mechanical-inflammatory coupled microenvironment models of microglia by culturing BV2 cells (a murine microglial cell line) on polyacrylamide gels with tunable stiffness and incorporating a lipopolysaccharide (LPS) to mimic the physiological and pathological microenvironment of microglia in the hippocampus. Through characterization of activation-related proteins, cytokines, and reactive oxygen species (ROS) levels, we observed that the LPS treatment induced microglia on a stiff matrix to exhibit overexpression of NOX2, higher levels of ROS and inflammatory factors compared to those on a soft matrix. Additionally, using scanning electrochemical microscopy (SECM), we performed in situ characterization and discovered that microglia on a stiff matrix promoted extracellular ROS production, leading to a disruption in their redox balance and increased susceptibility to LPS-induced ROS production. Furthermore, the respiratory activity and migration behavior of microglia were closely associated with their activation process, with the stiff matrix-LPS-induced microglia demonstrating the most pronounced changes in respiratory activity and migration ability. This work represents the first in situ and dynamic monitoring of microglia activation state alterations under a mechanical-inflammatory coupled microenvironment using SECM. Our findings shed light on matrix stiffness-dependent activation of microglia in response to an inflammatory microenvironment, providing valuable insights into the mechanisms underlying neuroinflammatory processes in the CNS.

Scanning gel electrochemical microscopy (SGECM): Elaboration and cross-linking of chitosan-based gel probes

Scanning gel electrochemical microscopy (SGECM) is based on gel probes that are in soft contact with the sample for local electrochemical analysis without needing an additional electrolyte solution. The reproducibility and reliability of the SGECM measurements call for high quality gel probes. In this work, the elaboration of gel probe by electrodeposition of chitosan on microelectrode is detailed, with the key parameters discussed, for the sake of achieving better shape control. For the gel probe fabricated with electrodeposited chitosan on a 25 μm disk microelectrode, deposition solutions with a pH of ca. 5.5 and microelectrodes with the Rg of 2∼3 are suggested. Cyclic voltammetry of the gel probe in contact with Pt surface shows lower current than that measured in solution by ‘classical’ scanning electrochemical microscopy, which may be related to the confinement effect. Moreover, an attempt to cross-link the gel by glutaraldehyde after electrodeposition is proposed. After cross-linking for 2 or 4 h, the strength of the chitosan hydrogel increases as supported by force sensing and SGECM approach-retract curves, while the electrochemical behavior of the gel probe is not significantly changed when immersed in 1 mM ferrocenedimethanol solution.