Due to their small size and large surface area-to-volume ratios, nanoparticles (particles with limiting dimensions smaller than 100 nm) have been widely applied as catalysts. Metal nanoparticles are typically produced in suspensions from metal ion precursors, reducing agents, and organic ligands called capping agents. Capping agents help prevent particle agglomeration, fix nanoparticle size, and promote monodispersity. However, capping agents also affect the morphology and the physico-chemical surface properties of nanoparticles, which can influence catalytic properties in unpredictable ways. While there have been extensive studies focused on examining the relationship between nanoparticle size, shape, composition and catalytic activity, relatively few have investigated the effects of capping agent properties on catalysis, and most studies involving nanoparticle catalysts have been conducted on collections, ensembles, or arrays of particles rather than single nanoparticles. Results obtained for systems composed of multiple nanoparticles dispersed on solid surfaces can be difficult to interpret due to variations in particle loading and interparticle distance, which are often challenging or impossible to control and characterize. The complexity of these unavoidable experimental variables may explain some of the seemingly inconsistent conclusions that have been drawn between nanoparticle properties and catalytic activity in recent reports. Single nanoparticle studies should help overcome limitations associated with investigations based on collections of nanoparticles by helping uncover direct relationships between nanoparticle size, surface properties, and catalytic activity that are unobscured by complex factors such as interparticle distance and particle loading. In this work, we aim to use nitrided carbon fiber ultramicroelectrodes to examine electrocatalytic properties of bare (uncapped) and capped gold nanoparticles at the single nanoparticle level.

Due to enhanced properties such as large surface area-to-volume ratio, metal nanoparticles are often employed as catalysts for various applications. However, most studies involving nanoparticle catalysts have been conducted on collections of particles rather than single nanoparticles. Results obtained for ensemble systems can be difficult to interpret due to variations in particle loading and interparticle distance, which are often challenging to control and characterize. In this study, two immobilization strategies for incorporating gold nanoparticles (AuNPs) on carbon fiber ultramicroelectrodes (UMEs) were compared with the goal of extending these techniques to nanoelectrodes for studies of single AuNPs. Both layer-by-layer deposition of AuNPs on natural carbon fiber UMEs and direct reduction of AuNPs on nitrided carbon fiber UMEs were explored. Although both methods proved feasible, the direct reduction method seemed to be more effective and should better enable direct comparisons of bare and capped AuNPs.