Microelectrochemical devices and methods for investigation of complex surface modifications and electroactive thin-films

Here we report on the development of microelectrochemical generation-collection flow devices and techniques for studies of complex electrode surface modifications and electroactive thin films. First we outline a new technique for microfluidic surface titrations (MSTs) of electroactive thin-films. One significant outcome of this project is that simple fabrication techniques can be used to prepare microelectrochemical generation-collection systems that have collection efficiencies up to 97%. Proof-of-concept studies of MSTs were initially performed by evaluating electrogenerated Au₂O₃. These studies show that MST is comparable to conventional methods for measuring electroactive surface adsorbed species, such as cyclic voltammetry. The technique was then optimized by performing MSTs of electrodeposited Cu. After the optimization we were able to measure surface concentrations of Cu as low as 30 pmol cm⁻². These studies were further extended to fundamental studies of electroactive self-assembled monolayers, demonstrating that in some cases we are able to detect electroactive moieties that are not close enough to the electrode surface to be detected by conventional methods. We also introduce a flow cell design which allows for complex ex situ surface modification of electrode substrates that would be difficult to implement and analyze using other bulk generation-collection techniques. Specifically, the flow cell allows us to study electrodes which have been modified using techniques that have been optimized for silicon wafers or glass slides. This is illustrated by proof of concept studies of the mechanisms of reactions at Pt dendrimer encapsulated nanoparticle (DENs) deposited on ultrathin Al₂O₃ films formed by atomic layer deposition. Pt DENs are studied in the presence and absence of ultrathin Al₂O₃ films. Additionally, DENs are studied before and after the dendrimers are removed using UV generated O₃. These studies suggest that evaluation of DENs can be performed after complex electrode surface modification, and that the dendrimer can be removed from the DENs without damaging the underlying Al₂O₃ layer. We hope that the methods and devices developed here advance the field of electroanalytical chemistry by complimenting well established techniques commonly performed by scanning electrochemical microscopy and rotating ring-disk voltammetry.