Scanning electrochemical microscopy: a new way of making electrochemical experiments

A short review is given on scanning electrochemical microscopy (SECM). The historic background of the technique is briefly summarized and the basic principles outlined. The three different directions of its use: chemical microscopic imaging, the measuring of physicochemical constants and coefficients, and use as a micromachining tool are briefly discussed. The general built-up of the SECM apparatus is described. Preparation and use of several different measuring tips are introduced. A few examples are given of the application of SECM measurement in different studies.     

Scanning electrochemical microscopy-development of instrumentation utilizing piezo-bimorph X-Y scanners

The development of the instrumentation of a scanning electrochemical microscopy (SECM) is presented. The core of the SECM sensing system is constructed based on piezobimorph scanners, a mechanical micropositioner of multi-dimensional adjustment and ultramicroelectrodes. The control of the electrochemical cell and the SECM system is realized by a battery powered bipoteniostat and analog control circuits respectively with the control of a microcomputer work station. The demonstrations of SECM experiments are given on both a standard IDA sample and a silver electrode. Discussions on the resolution and quality of SECM image are made.     

Scanning electrochemical microscopy for biosurface imaging

Scanning electrochemical microscopy (SECM) is a powerful technique that can provide chemical identity, quantification, and spatiotemporal information on biosurfaces. The ability of SECM for noninvasive and high-resolution electrochemical imaging has made it valuable for the study of cell phenotypes and functions. This review focuses on the latest advances of SECM technique for the biosurface imaging. The SECM measurements of different biomarkers, including oxygen consumption rate and enzyme activity of cell aggregates, redox state of cardiomyocytes, and bacterial metabolic activity, are introduced. The applicability of SECM on membrane permeability measurements, neurotransmitter measurements, and intracellular measurements is discussed.     

Chemical imaging of biological systems with the scanning electrochemical microscope

A brief overview on recent advances in the application of scanning electrochemical microscopy (SECM) to the investigation of biological systems is presented. Special emphasis is given to the mapping of local enzyme activity by SECM, which is exemplified by relevant original systems.     

Localised electrochemical impedance spectroscopy with high lateral resolution by means of alternating current scanning electrochemical microscopy

A new method for measuring local interfacial impedance properties with high lateral resolution was developed by combination of electrochemical impedance spectroscopy (EIS) with scanning electrochemical microscopy (SECM). Alternating current scanning electrochemical microscopy (AC-SECM) allowed to identify and visualise microscopic domains of different conductivity/electrochemical activities on solid/liquid interfaces immersed into an electrolyte. The performance of the method was illustrated by imaging an array of Pt-band microelectrodes in solutions of low conductivity in the absence of any redox mediator.     

Scanning electrochemical microscopy determination of organic soluble MPC electron-transfer rates

In this paper, we describe a novel method for measuring the forward heterogeneous electron-transfer rate constant (kf) through the thiol monolayer of gold monolayer protected clusters (MPCs) in solution using scanning electrochemical microscopy (SECM). Applying the equations for mixed mass-transfer and electron-transfer processes, we develop a new formula using only the diffusion coefficient and the tip radius and use it as part of a new method for evaluating SECM approach curves. This method is applied to determine the electron-transfer rates from a series of SECM approach curves for monodisperse hexanethiol MPCs and for polydisperse hexanethiol, octanethiol, decanethiol, dodecanethiol, and 2-phenyethylthiol gold MPCs. Our results show that as the alkanethiol length increases the rate of electron transfer decreases in a manner consistent with the previously proposed tunneling mechanism for the electron transfer in MPCs. However, the effective tunneling coefficient, Beta, is found to be only 0.41 A-1 for alkanethiol passivated MPCs compared to typical values of 1.1 A-1 for alkanethiols as self-assembled monolayers on two-dimensional gold substrates. Similar SECM approach curve results for Pt and Au MPCs indicate that the electron-transfer rate is dependent mostly on the composition of the thiol layer and not on differences in the core metal.     

Fabricating and imaging carbon-fiber immobilized enzyme ultramicroelectrodes with scanning electrochemical microscopy.

The scanning electrochemical microscope (SECM) is used to image the activity of enzymes immobilized on the surfaces of disk-shaped carbon-fiber electrodes. SECM was used to map the concentration of enzymatically produced hydroquinone or hydrogen peroxide at the surface of a 33-microm diameter disk-shaped carbon-fiber electrode modified by an immobilized glucose-oxidase layer. Sub-monolayer coverage of the enzyme at the electrode surface could be detected with micrometer resolution. The SECM was also employed as a surface modification tool to produce microscopic regions of enzyme activity by using a variety of methods. One method is a gold-masking process in which microscopic gold patterns act as mask for producing patterns of chemical modification. The gold masks allow operation in both a positive or negative process for patterning enzyme activity. A second method uses the direct mode of the SECM to produce covalently attached amine groups on the carbon surface. The amine groups are anchors for attachment of glucose oxidase by use of a biotin/avidin process. The effect of non-uniform enzyme activity was investigated by using the SECM tip to temporarily damage an immobilized enzyme surface. SECM imaging can observe the spatial extent and time-course of the enzyme recovery process.     

Quantitative characterization of shear force regulation for scanning electrochemical microscopy

The quest for higher spatial resolution in scanning electrochemical microscopy (SECM) calls for the application of smaller probe electrodes. When electrodes are to be used in the feedback mode, smaller electrodes require higher intrinsic kinetics at the sample. The fabrication of nanoelectrodes, as well as their use as SECM probes at constant distance, are reported. The properties of shear force regulation system are characterized quantitatively. Simultaneous topography and reactivity imaging were demonstrated using gold microstructures on a glass substrate.     

The local electrochemical behavior of the AA2098-T351 and surface preparation effects investigated by scanning electrochemical microscopy

In this work, scanning electrochemical microscopy (SECM) measurements were employed to characterize the electrochemical activities on polished and as-received surfaces of the 2098-T351 aluminum alloy (AA2098-T351). The effects of the near surface deformed layer (NSDL) and its removal by polishing on the electrochemical activities of the alloy surface were evaluated and compared by the use of different modes of SECM. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were also employed to characterize the morphology of the surfaces. The surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS). The surface generation/tip collection (SG/TC) and competition modes of the SECM were used to study hydrogen gas (H₂) evolution and oxygen reduction reactions, respectively. H₂ evolution and oxygen reduction were more pronounced on the polished surfaces. The feedback mode of SECM was adopted to characterize the electrochemical activity of the polished surface that was previously corroded by immersion in a chloride-containing solution, in order to investigate the influence of the products formed on the active/passive domains. The precorroded surface and as-received surfaces revealed lower electrochemical activities compared with the polished surface showing that either the NSDL or corrosion products largely decreased the local electrochemical activities at the AA2098-T351 surfaces.     

有机涂层／金属界面腐蚀的微区电化学

以扫描开尔文探针，局部交流阻抗和扫描电化学显微镜为代表的微区电化学技术以其高精度、高空间解析度的定域分析优势被广泛应用。本文简要介绍了这三种技术的测量原理和关键问题，并着重归纳了这些技术应用于有机涂层／金属界面腐蚀行为的研究成果，包括界面微区表观形貌的获取，不同界面腐蚀机制的推理验证及其影响因素的作用机理等，并对三种技...     

Tip current/positioning close-loop mode of scanning electrochemical microscopy for electrochemical micromachining

Scanning electrochemical microscopy (SECM) has been approved as a prospective electrochemical micromachining (ECMM) technique soon after its birth. However, it still remains challenge for SECM to fabricate arbitrary three-dimensional (3D) microstructures because of the limitation of positioning system. To solve this problem, we proposed a tip current signal/positioning close-loop mode in which the tip current signal is fed back to the positioning system in order to program the motion trial of SECM tip. Both the triedge-cone and sinusoidal microstructures were obtained by the close-loop positioning mode. The static-state etching process was demonstrated not to be disturbed by the slow motion rate of SECM tip. The unique positioning mode would be significant for both ECMM and electrochemical imaging.     

扫描电化学显微镜在生物医学领域的应用研究进展

研究病变细胞和组织的异常表现可为理解重大疾病发生发展的病理机理和新型药物筛选提供重要参考.扫描电化学显微镜(Scanning electrochemical microscopy, SECM)是一种基于电化学原理的扫描探针显微镜,通过记录探针在样品表面扫描时的电流或电位等信息,对活细胞的形态和多种化学信息进行原位、实时...     

Photosystem I patterning imaged by scanning electrochemical microscopy

We report the first directed adsorption of Photosystem I (PSI) on patterned surfaces containing discrete regions of methyl- and hydroxyl-terminated self-assembled monolayers (SAMs) on gold. SAM and PSI patterns are characterized by scanning electrochemical microscopy (SECM). The insulating protein complex layer blocks the electron transfer of the SECM mediator, thereby reducing the electrochemical current significantly. Uniformly and densely packed adsorbed protein layers are observed with SECM. Pattern images correlate with our previous studies where we showed that low-energy surfaces (e.g., CH3-terminated) inhibit PSI adsorption in the presence of Triton X-100, whereas high-energy surfaces (e.g., OH-terminated) enable adsorption. Therefore, a SAM pattern with alternating methyl and hydroxyl surface regions allows PSI adsorption only on the hydroxyl surface, and this is demonstrated in the resulting SECM images.     

Investigation of ion-bombarded conducting polymer films by scanning electrochemical microscopy (SECM)

Scanning electrochemical microscopy (SECM) was used to investigate the effect of ion bombardment on thin films of the conducting polymers poly[3-ethoxy-thiophene] (PEOT) and poly[ethylenedioxy-thiophene] (PEDT). Bombardment with Ar+-ions converts the topmost 30 nm thick layer to an essentially insulating material. SECM approach curves as well as two dimensional scans prove the existence of regions of different conductivity within the irradiated regions that did not show a significant dependence on ion dosage. PEDT layers patterned by ion bombardment through microscopic masks are investigated as prototypes of miniaturized printed circuit boards that can be formed by galvanic copper deposition onto conducting PEDT. Defects in conducting polymer patterns were analyzed by SECM imaging before any deposition of copper. Appropriate representations of SECM images for the evaluation of this technologically important question are discussed.     

Investigation of ion-bombarded conducting polymer films by scanning electrochemical microscopy (SECM)

Scanning electrochemical microscopy (SECM) was used to investigate the effect of ion bombardment on thin films of the conducting polymers poly[3-ethoxy-thiophene] (PEOT) and poly[ethylenedioxy-thiophene] (PEDT). Bombardment with Ar⁺-ions converts the topmost 30 nm thick layer to an essentially insulating material. SECM approach curves as well as two dimensional scans prove the existence of regions of different conductivity within the irradiated regions that did not show a significant dependence on ion dosage. PEDT layers patterned by ion bombardment through microscopic masks are investigated as prototypes of miniaturized printed circuit boards that can be formed by galvanic copper deposition onto conducting PEDT. Defects in conducting polymer patterns were analyzed by SECM imaging before any deposition of copper. Appropriate representations of SECM images for the evaluation of this technologically important question are discussed.     

Characterization of carboxylic acid-terminated self-assembled monolayers by electrochemical impedance spectroscopy and scanning electrochemical microscopy

Electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) are used to monitor changes in the ionization of monolayers of 11-mercaptoundecanoic acid. When using an anionic redox probe, Fe(CN)6(-4), the charge-transfer resistance of the 11-mercaptoundecanoic acid monolayer-modified interface increases in a sigmoidal fashion as the solution is made basic. The opposite effect is observed when using a cationic redox probe. The inflection points of these two titration curves, however, differ when using the different redox probes. This result is taken as being characteristic of the influence that applied potential has on the ionization of the monolayer. The role of substrate potential on the ionization of the monolayer is further investigated by SECM. The SECM measurement monitors the concentration of Ru(NH3)6(+3) as the potential of the substrate is varied about the potential of zero charge. For monolayers of 11-mercaptoundecanoic acid in solutions buffered near the pKa of the terminal carboxylic acid, potential excursions positive of the PZC cause an increase in the concentration of Ru(NH3)6(+3) local to the interface, and potential excursions negative of the PZC cause a decrease in the local concentration of Ru(NH3)6(+3). Similar experiments conducted with an interface modified with 11-undecanethiol had no impact on the local concentration of Ru(NH3)6(+3). These results are interpreted in terms of the influence that applied potential has on the pH of the solution local to the interface and the impact that this has on the ionization of the monolayer.     

Biological applications of scanning electrochemical microscopy: chemical imaging of single living cells and beyond

Recent applications of scanning electrochemical microscopy (SECM) to studies of single biological cells are reviewed. This scanning probe microscopic technique allows the imaging of an individual cell on the basis of not only its surface topography but also such cellular activities as photosynthesis, respiration, electron transfer, single vesicular exocytosis and membrane transport. The operational principles of SECM are also introduced in the context of these biological applications. Recent progress in techniques for high-resolution SECM imaging are also reviewed. Future directions, such as single-channel detection by SECM, high-resolution imaging with nanometer-sized probes, and combined SECM techniques for multidimensional imaging are also discussed.     

Modification and characterization of artificially patterned enzymatically active surfaces by scanning electrochemical microscopy

This review summarizes the characterization of localized enzymatic activity by scanning electrochemical microscopy (SECM). After introducing the concepts of feedback imaging and generator-collector experiments with enzyme-modified solid surfaces, a comparison of the merits and limitations of both approaches is given and further illustrated by selected applications. They include enzyme-modified patterned monolayers, enzyme-modified polymer microstructures and enzyme-modified metal microstructures. Such configurations are important for the development of miniaturized bioanalytical systems with proteins, such as miniaturized enzyme electrode arrays. SECM has emerged as an ideal tool for prototyping of such systems. It also offers several mechanisms for local surface modifications under conditions compatible with conservation of protein functionality of enzymes and antibodies. The subsequent imaging of the immobilized activity provides direct information about local immobilized enzyme activity. The range of biotechnological applications can be expanded by labeling other biomolecules, such as monoclonal antibodies, with appropriate enzymes. Miniaturized electrochemical enzyme immunoassays that apply the sandwich format and SECM as the detection method are reviewed. They have been performed on microstructured supports after reagent spotting or on agglomerates of surface-modified magnetic microbeads. Finally, current challenges are listed with indications of ongoing research to overcome current limitations by means of instrumental improvements.     

Constant-distance mode scanning electrochemical microscopy (SECM)--Part I: Adaptation of a non-optical shear-force-based positioning mode for SECM tips

A non-optical shear-force-based detection scheme for accurately controlling the tip-to-sample distance in scanning electrochemical microscopy (SECM) is presented. With this approach, the detection of the shear force is accomplished by mechanically attaching a set of two piezoelectric plates to the scanning probe. One of the plates is used to excite the SECM tip causing it to resonate, and the other acts as a piezoelectric detector of the amplitude of the tip oscillation. Increasing shear forces in close proximity to the sample surface lead to a damping of the vibration amplitude and a phase shift, effects that are registered by connecting the detecting piezoelectric plate to a dual-phase analogue lock-in amplifier. The shear force and hence distance-dependent signal of the lock-in amplifier is used to establish an efficient, computer-controlled closed feedback loop enabling SECM imaging in a constant-distance mode of operation. The details of the SECM setup with an integrated piezoelectric shear-force distance control are described, and approach curves are shown. The performance of the constant-distance mode SECM with a non-optical detection of shear forces is illustrated by imaging simultaneously the topography and conductivity of an array of Pt-band microelectrodes.     

Scanning Electrochemical Microscopy (SECM) Investigation of 3D Printed Parts Produced by CMT Welding Technology

In the field of manufacturing technology an exciting revolution is in progress today. The different methods of the so called additive manufacturing (AM) technologies are under fast developments. Several versions of them are called 3D printing. Less interest has been given to study the corrosion resistance character of the differently made 3D printed metal alloy items. In this work corrosion behaviour of 3D printed AlMg4.5Mn0.7 alloy samples were investigated. Conventional methods like open circuit potential measurements, Tafel plots taking and scanning electrochemical microscopy (SECM) – with pH measuring tungsten micro‐tip and micro‐disc type Pt electrode were used. The metal samples were embedded in epoxy resin. 2D SECM images and line scans were made to see the local changes of oxygen concentration. Flame atomic absorption spectroscopy was used for measuring the metal composition of manufacturing wire and printed sample. The local activity of the surface spots were measured using approach curves recorded in case of ferrocene methanol mediator.