Imaging Transient Formation of Diffusion Layers with Fluorescence-Enabled Electrochemical Microscopy

Abstract

Fluorescence-enabled electrochemical microscopy (FEEM) is demonstrated as a new technique to image transient concentration profiles of redox species generated on ultramicroelectrodes (UMEs). FEEM converts an electrical signal into an optical signal by electrically coupling a conventional redox reaction to a fluorogenic reporter reaction on a closed bipolar electrode. We describe the implementation of FEEM for diffusion layer imaging and use an array of thousands of parallel bipolar electrodes to image the diffusion layers of UMEs in two and three dimensions. This new technique provides a way to image an entire 2-dimensional lateral cross section of a dynamic diffusion layer in a single experiment. By taking several of these lateral cross sections at different axial positions in the diffusion layer, a 3-dimensional image of the diffusion layer can be built. We image the diffusion layer of a 10 μm diameter carbon fiber electrode over the course of a cyclic voltammetry experiment and compare the FEEM-generated images to concentration profiles generated from numerical simulation. We also image the diffusion layer of a two electrode array consisting of two 10 μm diameter carbon fibers over the course of a potential step experiment.

Electrogenerated Chemiluminescence Reporting on Closed Bipolar Microelectrodes and the Influence of Electrode Size

“…We also chose to focus our studies on bipolar microelectrodes (loosely defined here as having a critical dimension of less than ≈100 μm), as we believe that one of the more promising uses of closed BPEs is their microelectrode array‐based use in electrochemical imaging. Our group recently demonstrated this in a method we call fluorescence‐enabled electrochemical microscopy (FEEM), which uses a fluorogenic redox reaction to report faradaic current through closed BPEs and large‐scale arrays thereof . It is easy to imagine an analogous method, in which ECL is used as the optical reporter in place of a fluorogenic reaction.…”

Active Junctions to Improve Sensitivity and Detection Limit of a Microdevice Based on Coulometry Coupled with Silver Metallization

“…Thus, if the liquid junction can be replaced by a metal junction, it will facilitate device fabrication. Metal junctions have been used in some electrochemical systems of conventional sizes , incorporating the techniques developed in closed bipolar electrochemistry .…”

Detection of Transient Nanoparticle Collision Events Using Electrochemiluminescence on a Closed Bipolar Microelectrode

“…Massive parallel arrays containing tens to hundreds of thousands c-BPEs can be used and simultaneously monitored using ECL or fluorescence. [24][25][26][27][28] Their utilization has become a unique strategy for monitoring large-scale heterogeneous electron-transfer events. When redox-generated light is used to measure the faradaic response, each electrode in a large array serves as an equivalent optical pixel for wide-scale spatial resolution of electrochemical processes.…”

“…Previous BPE-based imaging applications have mainly focused on long-timescale and steady-state measurements. [24,26,30] Although ECL and fluorescence have been used to study nanoparticle collision, light was not generated across a closed-bipolar electrode. Instead, the optical signal was produced directly from the particle itself.…”