Scanning Electrochemical Microscopy Analyses of Surfaces Using Ferrocenated Gold Nanoparticle Mediators

High Resolution Image Download MS PowerPoint Slide Small ferrocenated gold nanoparticles, meaning ferrocenyl-functionalized nanoparticles with an approximate radius of 2 nm, were evaluated as redox mediators for surface analysis in scanning electrochemical microscopy (SECM) experiments in feedback mode. In the presence of a bulky anion electrolyte (BarF – ), these nanoparticles are sufficiently soluble in dichloromethane (CH 2 Cl 2 ) in both their reduced and oxidized states for such analyses in organic media. The SECM approach curves were analyzed using the Cornut–Lefrou approximations on several types of substrates. When the nanoparticles are used to probe either a conducting substrate, such as carbon, or an insulating substrate, such as glass, the experimental results are in good agreement with the theoretical behavior expected for diffusion-controlled processes. On a modified substrate coated with a COOH-terminated organic layer, interactions between the nanoparticles and the surface were detected. These interactions led to an enhancement of the positive feedback response of the approach curve due to lateral charge transport at the interface, while electron transfer through the organic layer remained negligible. All curves were quantified using the Cornut–Lefrou equation. This simple treatment of nanoparticle–surface interactions using the SECM approach curves associated with analytical approximations appears as an effective way to probe the affinity of redox nanoparticles for a surface, as reflected by an increase in the positive feedback response. Since the method does not require an electrical connection to the sample, and considering the versatility of the nanoparticle preparation, this approach could be applied to a wide range of substrates, whether conducting or insulating.