Scanning electrochemical microscopy (SECM): localized glucose oxidase immobilization via the direct electrochemical microspotting of polypyrrole–biotin films

Visualizing Electrochemical CO2 Conversion via the Emerging Scanning Electrochemical Microscope: Fundamentals, Applications and Perspectives

With the rapid development and maturity of electrochemical CO2 conversion involving cathodic CO2 reduction reaction (CO2RR) and anodic oxygen evolution reaction (OER), conventional ex situ characterizations gradually fall behind in detecting real-time products distribution, tracking intermediates, and monitoring structural evolution, etc. Nevertheless, advanced in situ techniques, with intriguing merits like good reproducibility, facile operability, high sensitivity, and short response time, can realize in situ detection and recording of dynamic data, and observe materials structural evolution in real time. As an emerging visual technique, scanning electrochemical microscope (SECM) presents local electrochemical signals on various materials surface through capturing micro-current caused by reactants oxidation and reduction. Importantly, SECM holds particular potentials in visualizing reactive intermediates at active sites and obtaining instantaneous morphology evolution images to reveal the intrinsic reactivity of active sites. Therefore, this review focuses on SECM fundamentals and its specific applications toward CO2RR and OER, mainly including electrochemical behavior observation on local regions of various materials, target products and onset potentials identification in real-time, reaction pathways clarification, reaction kinetics exploration under steady-state conditions, electroactive materials screening and multi-techniques coupling for a joint utilization. This review undoubtedly provides a leading guidance to extend various SECM applications to other energy-related fields.

Fast detection of micro-objects using scanning electrochemical microscopy based on visual recognition and machine learning

Scanning electrochemical microscopy (SECM) is a scanning probe microscope with an ultramicroelectrode (UME) as a probe. The technique is advantageous in the characterization of the electrochemical properties of surfaces. However, the limitations, such as slow imaging and many functions depending on the user, only allow us to use some of the possibilities. Therefore, we applied visual recognition and machine learning to detect micro-objects from the image and determine their electrochemical activity. The reconstruction of the image from several approach curves allows it to scan faster and detect active areas of the sample. Therefore, the scanning time and presence of the user is diminished. An automated scanning electrochemical microscope with visual recognition has been developed using commercially available modules, relatively low-cost components, design, software solutions proven in other fields, and an original control and data fusion algorithm.

Operando Scanning Electrochemical Probe Microscopy during Electrocatalysis

Scanning electrochemical probe microscopy (SEPM) techniques can disclose the local electrochemical reactivity of interfaces in single-entity and sub-entity studies. Operando SEPM measurements consist of using a SEPM tip to investigate the performance of electrocatalysts, while the reactivity of the interface is simultaneously modulated. This powerful combination can correlate electrochemical activity with changes in surface properties, e.g., topography and structure, as well as provide insight into reaction mechanisms. The focus of this review is to reveal the recent progress in local SEPM measurements of the catalytic activity of a surface toward the reduction and evolution of O₂ and H₂ and electrochemical conversion of CO₂. The capabilities of SEPMs are showcased, and the possibility of coupling other techniques to SEPMs is presented. Emphasis is given to scanning electrochemical microscopy (SECM), scanning ion conductance microscopy (SICM), electrochemical scanning tunneling microscopy (EC-STM), and scanning electrochemical cell microscopy (SECCM).

Scanning electrochemical microscopy in the development of enzymatic sensors and immunosensors

Scanning electrochemical microscopy (SECM) is very useful, non-invasive tool for the analysis of surfaces pre-modified with biomolecules or by whole cells. This review focuses on the application of SECM technique for the analysis of surfaces pre-modified with enzymes (horseradish peroxidase, alkaline phosphatase and glucose oxidase) or labelled with antibody-enzyme conjugates. The working principles and operating modes of SECM are outlined. The applicability of feedback, generation-collection and redox competition modes of SECM on surfaces modified by enzymes or labelled with antibody-enzyme conjugates is discussed. SECM is important in the development of miniaturized bioanalytical systems with enzymes, since it can provide information about the local enzyme activity. Technical challenges and advantages of SECM, experimental parameters, used enzymes and redox mediators, immunoassay formats and analytical parameters of enzymatic SECM sensors and immunosensors are reviewed.

Electrochemically "writing" graphene from graphene oxide

A novel approach of patterning graphene on conductive surfaces based on local electrochemical reduction of graphene oxide is reported. Graphene is "written" from typical graphene oxide dispersion by applying negative potential on conductive surfaces vs. a micrometer-sized counter electrode "pen" with scanning electrochemical microscopy (SECM). Micrometer scaled patterns are successfully generated on gold and stainless steel surfaces.

Detection of hydrogen peroxide produced during the oxygen reduction reaction at self-assembled thiol-porphyrin monolayers on gold using SECM and nanoelectrodes

Porphyrin molecules were immobilized on polycrystalline gold and glassy carbon by coordinating cobalt(II) 5,10,15,20-tetraphenyl-21H,23H-porphine to a 4-aminothiophenol self-assembled monolayer. The resulting electrocatalytic activity of the metalloporphyrin-modified substrates with regard to the oxygen reduction reaction was characterized by means of cyclic voltammetry and scanning electrochemical microscopy (SECM) using nanoelectrodes of well-defined geometry. From substrate generation tip collection (SG-TC) mode SECM measurements performed under steady-state conditions and at different applied substrate potentials, it is possible to extract kinetic information relevant to electrocatalyst substrates such as metalloporphyrin-modified gold and glassy-carbon electrodes. Such an approach allows for the isolation of the unique contribution of the electrocatalyst to the oxygen reduction reaction and peroxide formation.

Scanning electrochemical microscopy (SECM) as a tool in biosensor research

Scanning electrochemical microscopy (SECM) is discussed as a versatile tool to provide localized (electro)chemical information in the context of biosensor research. Advantages of localized electrochemical measurements will be discussed and a brief introduction to SECM and its operation modes will be given. Experimental challenges of the different detection modes of SECM and its applicability for different fields in biosensor research are discussed. Among these are the evaluation of immobilization techniques by probing the local distribution of biological activity, the visualization of diffusion profiles of reactants, cofactors, mediators, and products, and the elucidation of (local) kinetic parameters. The combination of SECM with other scanning-probe techniques allows to maximize the information on a given biosensing system. The potential of SECM as a tool in micro-fabrication aiming for the fabrication of microstructured biosensors will be shortly discussed.

Theory of Polymer Entrapped Enzyme Ultramicroelectrodes: Fundamentals

We have developed a theoretical description of the amperometric response of ultramicroelectrode (UME) biosensors formed via enzyme entrapment. Our model allows for multiple enzymes and co-substrates, and results in a closed-form analytical expression for the steady-state current response of the disk ultramicroelectrode. It captures the effects of enzyme-entrapment domain size, species transport properties (which can be different in the polymer and surrounding electrolyte), enzyme kinetics, and axisymmetric diffusion. Assumptions inherent in the derivation are carefully explained, as are the resulting limits on the applicability of the results. The ability to theoretically predict the response of enzyme entrapped UMEs should enable improved design, operation, and data interpretation for this important class of biosensors.

Advances in the application of scanning electrochemical microscopy to bioanalytical systems

Scanning electrochemical microscopy (SECM) is a powerful surface characterisation technique that allows for the electrochemical profiling of surfaces with sub micrometer resolution. While SECM has been most widely used to electrochemically study and profile non-biological surfaces and processes, the technique has in recent years, been increasingly used for the study of biological systems - and this is the focus of this review. An overview of SECM and how the technique may be applied to the study of biological systems will first be given. SECM and its application to the study of cells, enzymes and DNA will each be considered in detail. The review will conclude with a discussion of future directions and scope for further developments and applications.

Scanning electrochemical microscopy in the 21st century

The fundamentals of and recent advances in scanning electrochemical microscopy (SECM) are described. The focus is on applications of this method to studies of systems and processes of active current interest ranging from nanoelectrochemistry to electron transfer reactions and electrocatalysis to biological imaging.

Imaging of DNA hybridization on microscopic polypyrrole patterns using scanning electrochemical microscopy (SECM): the HRP bio-catalyzed oxidation of 4-chloro-1-naphthol

We illustrate in this paper the successful combination of the direct and feedback mode of scanning electrochemical microscopy (SECM) for the writing of oligonucleotide patterns on thin gold films alongside the imaging of DNA hybridization. The patterning process was achieved using the direct mode of SECM, where the electrical field established between the SECM tip and the gold interface was used to drive the local deposition of micrometre sized polypyrrole spots to which a 15(mer) oligonucleotide (ODN) strand was linked covalently. Imaging of the deposited polypyrrole-ODNs was achieved by means of the feedback mode of SECM using Ru(NH(3))(6)(3+) as the mediator. The detection of the hybridization reaction of the ODN probes with their biotinylated complementary strands using SECM was possible after subsequent reactions with streptavidin and biotinylated horseradish peroxidase (HRP). The HRP-biocatalyzed oxidation of 4-chloro-1-naphthol (1) in the presence of H(2)O(2), and the precipitation of the insoluble product 4-chloro-1-naphthon (2) on the hybridized areas on the gold film caused a local alteration of conductivity. Such a change in conductivity was sensitively detected by the SECM tip and allowed imaging of DNA arrays in a fast and straightforward way.