Scanning Electrochemical Microscopy
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Scanning electrochemical microscopy (SECM) is a method of local probe microscopy based on the displacement of an ultramicroelectrode (UME) in the vicinity of an interface. The UME has at least one dimension in the micrometer range. It is extremely useful in modern electroanalysis for the characterization of surfaces by imaging electroactive and non-electroactive materials or for obtaining quantitative data on specific analytes or processes by studying the reactions occurring on the surface of a substrate. It operates through several modes (feedback, generation/collection, penetration etc…) and allows evaluating kinetics of chemical reactions, studying biological cells, achieving localized surface modifications or imaging surfaces. More recently, scanning electrochemical cell microscopy (SECCM) was developed to allow obtaining high spatial resolution images. SECCM is derived from SECM and consists of a probe which is a sharp double barrel capillary (nanopipette), with both compartments containing a quasi-reference electrode or quasi-reference counter electrode (QRCE) and filled with an electrolytic solution.Keywords:
Scanning Electrochemical Microscopy
Ultramicroelectrode
Scanning Probe Microscopy
Chemical Imaging
Micrometer
Characterization
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Abstract Scanning electrochemical microscopy (SECM) involves the measurement of current through an ultramicroelectrode (UME) tip when it is held or moved in a solution in the vicinity of a substrate. The substrate perturbs the electrochemical response of the tip, and this perturbation provides information about the nature and properties of the substrate. SECM has the advantage of very high spatial resolution and versatility for the detection of both electroactive and nonelectroactive species. It combines the virtues of electrochemistry at UMEs with those of an adjustable thin‐layer cell and allows one to make steady‐state measurements of the type carried out with the rotating ring‐disk electrode (RRDE), but with greater ease in fabrication, comparable rates of mass transfer, and without the requirement of forced convection. SECM has been applied to studies involving many different kinds of systems including electrode surfaces, liquid–liquid interfaces, and biological samples with micrometer and nanometer resolution. Commercial SECM systems exist, which facilitate such investigations.
Scanning Electrochemical Microscopy
Ultramicroelectrode
Micrometer
Nanometre
Electrochemical cell
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The incorporation of a shear-force (SF) feedback in scanning electrochemical microscopy (SECM) hardware has enabled topographically resolved electrochemical imaging of electroactive substrates. Despite the versatility of SECM-SF imaging, structural response of the ultra-microelectrode (UME) to various excitation inputs is poorly understood and predictive mathematical models for characterizing dynamic behavior, particularly at high operating frequencies (>100 kHz), are absent. In this article, we present a finite element model to characterize SF behavior by modeling the UME as a rigid cantilever with two distributed piezoelectric wafers (dither and receiver) and demonstrate the model’s ability to predict experimentally observed SF behavior. The obtained SF response under different dither-to-receiver distances for various UME geometries and loading conditions provides insight to the optimum placement of piezoelectric wafers on the UME for achieving a high SF amplitude at SF-sensitive frequencies. In addition, the variations in SF response under different dither-to-receiver orientations indicate the existence of a system transfer function that is dependent on the operating modes of the receiver. The agreement between simulated and experimental results suggests that the finite element model along with the experimental methodology can be extended to automated SF imaging using SECM hardware.
Dither
Scanning Electrochemical Microscopy
SIGNAL (programming language)
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Scanning Electrochemical Microscopy
Scanning Probe Microscopy
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Scanning electrochemical microscopy is a scanning probe technique that is based on faradaic current changes as a small electrode is moved across the surface of a sample. The images obtained depend on the sample topography and surface reactivity. The response of the scanning electrochemical microscope is sensitive to the presence of conducting and electroactive species, which makes it useful for imaging heterogeneous surfaces. The principles and instrumentation used to obtain images and surface reaction-kinetic information are discussed, and examples of applications to the study of electrodes, minerals, and biological samples are given.
Scanning Probe Microscopy
Scanning Electrochemical Microscopy
Instrumentation
Faradaic current
Chemical Imaging
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We describe voltage-switching mode scanning electrochemical microscopy (VSM-SECM), in which a single SECM tip electrode was used to acquire high-quality topographical and electrochemical images of living cells simultaneously. This was achieved by switching the applied voltage so as to change the faradaic current from a hindered diffusion feedback signal (for distance control and topographical imaging) to the electrochemical flux measurement of interest. This imaging method is robust, and a single nanoscale SECM electrode, which is simple to produce, is used for both topography and activity measurements. In order to minimize the delay at voltage switching, we used pyrolytic carbon nanoelectrodes with 6.5–100 nm radii that rapidly reached a steady-state current, typically in less than 20 ms for the largest electrodes and faster for smaller electrodes. In addition, these carbon nanoelectrodes are suitable for convoluted cell topography imaging because the RG value (ratio of overall probe diameter to active electrode diameter) is typically in the range of 1.5–3.0. We first evaluated the resolution of constant-current mode topography imaging using carbon nanoelectrodes. Next, we performed VSM-SECM measurements to visualize membrane proteins on A431 cells and to detect neurotransmitters from a PC12 cells. We also combined VSM-SECM with surface confocal microscopy to allow simultaneous fluorescence and topographical imaging. VSM-SECM opens up new opportunities in nanoscale chemical mapping at interfaces, and should find wide application in the physical and biological sciences.
Scanning Electrochemical Microscopy
Fluorescence-lifetime imaging microscopy
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Amperometry
Scanning Probe Microscopy
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Scanning Electrochemical Microscopy
Micropatterning
Characterization
Scanning Probe Microscopy
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Gold electrodes integrated into silicon scanning force microscopy (SFM) probes allow the acquisition of spatially correlated data for sample morphology (via SFM) and local electrochemical reactivity via scanning electrochemical microscopy (SECM). The lateral resolution of both techniques is controlled by different properties of the integrated probes. The topographic tracking provided by the SFM mechanism allows the realization of very small working distances for the SECM measurements. Microfabrication technology was used in order to reduce the size of the active electrode area of the tip into the sub-100 nm regime. The functionality of the probes was tested using electrochemical methods. Experiments revealed that the response could be quantitatively compared to numerical simulation. The low working distance, in combination with the small size of the active electrode area, allows for high lateral resolution in the SECM images. This is illustrated with different model substrates that cover a range of different rate constants and illustrate the dependence of the SECM contrast on the local kinetics of the sample in the sub-micrometre size range.
Scanning Electrochemical Microscopy
Scanning Probe Microscopy
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Scanning Electrochemical Microscopy
Scanning Probe Microscopy
Pipette
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