Simultaneous Interfacial Reactivity and Topography Mapping with Scanning Ion Conductance Microscopy

Abstract

Scanning ion conductance microscopy (SICM) is a powerful technique for imaging the topography of a wide range of materials and interfaces. In this report we develop the use and scope of SICM, showing how it can be used for mapping spatial distributions of ionic fluxes due to (electro)chemical reactions occurring at interfaces. The basic idea is that there is a change of ion conductance inside a nanopipette probe when it approaches an active site, where the ionic composition is different to that in bulk solution, and this can be sensed via the current flow in the nanopipette with an applied bias. Careful tuning of the tip potential allows the current response to be sensitive to either topography or activity, if desired. Furthermore, the use of a distance modulation SICM scheme allows reasonably faithful probe positioning using the resulting AC response, irrespective of whether there is a reaction at the interface that changes the local ionic composition. Both strategies (distance modulation or tuned bias) allow simultaneous topographyactivity mapping with a single channel probe. The application of SICM reaction imaging is demonstrated on several examples, including voltammetric mapping of electrocatalytic reactions on electrodes and high-speed electrochemical imaging at rates approaching 4 s per image frame.These two distinct approaches provide movies of electrochemical current as a function of potential with hundreds of frames (images) of surface reactivity, to reveal a wealth of spatiallyresolved information on potential (and time) -dependent electrochemical phenomena. The experimental studies are supported by detailed finite element method modeling that places the technique on a quantitative footing.

Face-Discriminating Dissolution Kinetics of Furosemide Single Crystals: In Situ Three-Dimensional Multi-Microscopy and Modeling

“…have been used to acquire images of the topography of soft surfaces36,64 and for local ion current measurements [65][66][67]. Most recently, a new method based on the application of an oscillating bias between both QRCEs to generate an alternating ion current (AC) feedback signal, bias modulated SICM (BM─SICM), 47 has been introduced.…”

Nanopore Sensing

“…221 An elegant approach reported by Unwin and co-workers has demonstrated use of a bare nanopipette for dynamic visualization of interfacial reactivity without further electrode fabrication procedures. 222 The basic principle is simple yet intriguing: the ion current recorded by the pipet sensor is extremely sensitive to local conductivity change, and local conductivity depends on the ion composition in the solution. Therefore, as the probe is positioned in close proximity to an electrochemical reaction center that produces or consumes specific ions, the dynamic process can be sensed by the probe in the form of ion current as the conductivity changes.…”

Multifunctional scanning ion conductance microscopy

“…Constantdistance scanning is usually performed in a raster scan pattern [1,2,4,48], where line-by-line maps are generated, with a typical scan profile shown in figure 2b. More recently, a spiral scan profile has been introduced into SICM experiments [43,49], also depicted in figure 2b, greatly increasing image acquisition rates. In this configuration, the piezo positioners used to control the nanopipette (or sample) movement in the x-y plane are moving continuously.…”

“…The nanopipette current has been normalized by the value at the point of the closest approach (at each individual pixel) with the substrate potential held at −0.2 V (no substrate reaction). Adapted with permission from [43]. Copyright © 2016 American Chemical Society.…”