Scanning Electrochemical Microscopy (SECM):  An Investigation of the Effects of Tip Geometry on Amperometric Tip Response

Abstract

Transient and steady-state amperometric tip responses were simulated with an alternating direction implicit algorithm. Compared with previous publications, the simulation domain was designed to account for the diffusion of the redox species around the corner of the insulating sheath. Expanding space and time grids were used to optimize the algorithm, and the simulation was validated by comparison with published data for the microdisk electrode. Tip responses were simulated for a wide range of tip substrate distances over conducting and insulating substrates. The shape of the approach curves was investigated for several electroactive disk to insulator radii ratios. Diffusion around the edge of the insulating sheath was found to have a pronounced effect on the approach curves. In contrast to the findings of earlier studies, tip currents for conducting substrates were found to significantly depend on the tip geometry. The parameters of functions used to describe approach curves in the SECM literature were studied for several tip geometries commonly used experimentally. Simulated results were also used to assess the topographical sensitivity (the rate of change of tip current with respect to tip−substrate distance) and spatial resolution (the ability of the microdisk to distinguish two conducting islands inlaid into an insulating substrate) of the scanning electrochemical microscope (SECM).

Topographical and electrochemical nanoscale imaging of living cells using voltage-switching mode scanning electrochemical microscopy

“…1B) were used to produce theoretical approach curves for the same tip geometric parameters. The current profiles were fitted to established theoretical curves for a simple disk geometry (30)(31)(32). Good correlation was observed between theory and experiment.…”

Shape-selective transport through rectangle-based molecular materials: Thin-film scanning electrochemical microscopy studies

“…where L is the ratio of tip height above the substrate to tip radius, and k 1 , k 2 , k 3 , and k 4 are geometric factors that depend on the relative radii of the tip electrode and its insulating sheath (35,36). For the quantitative measurements described below, L was generally 1, as in previous work (17).…”

“…Based on well-established current-distance ''approach curves'' and associated theory (23,(29)(30)(31)(32)(33)(34)(35)(36), the controlled attenuation serves to position the tip electrode at a well-defined and highly reproducible distance above the platform. With the distance fixed, the SECM electrode potentials were switched to positive feedback mode, and the tip current was recorded.…”

“…Under feedback conditions, with the tip electrode close to the generation electrode, i ϱ is enhanced as follows (35,36):…”

Quantitative Local Photosynthetic Flux Measurements at Isolated Chloroplasts and Thylakoid Membranes Using Scanning Electrochemical Microscopy (SECM)

“…19 The geometry of the SECM tip, and the ability to place it at a defined distance from a sample, allows the flux of the redox-active species at the sample to be calculated from the current measured, by solving the underlying mass transport problem. [20][21][22] SECM is proving increasingly popular for studying living cell monolayers and individual cells. [23][24][25][26][27][28][29][30][31][32][33][34] Particularly relevant to this study are previous reports on aspects of photosynthesis, 35,36 for example, measurements of the local oxygen flux from single stomata of Brassica juncea 37 and the local oxygen flux above individual guard cells in intact plant leaves.…”