Stochastic Impact Electrochemistry of Alkanethiolate-Functionalized Silver Nanoparticles

This study uses single-impact experiments to explore how the nanoparticles' surface chemistry influences their redox activity. 20 and 40 nm-sized silver nanoparticles are functionalized with alkanethiol ligands of various chain lengths (n = 3, 6, 8, and 11) and moieties (carboxyl ─COOH / hydroxyl ─OH), and the critical role of the particle shell is systematically examined. Short COOH-terminated ligands enable efficient charge transfer, resulting in higher impact rates and fast, high-amplitude transients. Even elevated potentials fail to overcome tunneling barriers for ligand lengths of n ≥ 6 and risk oxidizing the electrode, forming an insulating layer. Electrostatic interactions play a key role in governing reaction dynamics. In general, particles with a COOH-group exhibit higher impact rates and current amplitudes in KCl than those with an OH-group. This effect is more pronounced for 40 nm-sized particles; although, they rarely oxidize completely. The influence of electrolyte composition-concentration, pH, and a biologically relevant electrolyte-reveals that its impact on the redox activity can be as critical as that of the particle shell, with both determining particle adsorption and electron tunneling. These findings provide insights into the complex interdependencies at the electrode-particle-electrolyte interface, aiding the design of custom redox-active (silver) nanoparticles for ultrasensitive electrochemical sensing.