Electrochemical deposition of gold nanoparticles on carbon ultramicroelectrode arrays

Electrode surfaces functionalized with gold nanoparticles (AuNP) are widely used in electroanalysis, electrocatalysis, and electrochemical biosensing due to their increased surface area and conductivity. Electrochemical deposition of AuNPs offers advantages over chemical synthesis, including better control over AuNP size, dispersion, and morphology. This study examines the electrodeposition of AuNPs on carbon ultramicroelectrode arrays (CUAs) focusing on electrodeposition parameters, such as deposition potential, deposition time, and gold ion concentration. Detailed analysis based on scanning electron microscopy revealed that higher reductive potentials and shorter deposition times result in smaller AuNP particle sizes and greater particle counts. Unlike previous studies using planar, macro-sized electrodes and millimolar concentrations of gold ion, as well as longer deposition times (e.g., 100-300 s), this research employed micromolar concentration ranges (25-50 μM) of gold ion solution and shorter deposition times (5-60 s) for successful electrodeposition of AuNPs on the array-based CUAs. This is attributed to the physical properties of the ultramicroelectrodes in the array geometry and the distinct material composition of the CUAs. The gold amounts deposited on the CUA electrodes were determined (88.73 ± 0.06 nmol cm^-2), which were in correlation with the electrocatalytic responses for the hydrogen evolution reaction (HER) measured on AuNP-modified CUAs. Overall, the array-based geometry, nanometer-scale electrode sizes, and unique material composition of the CUAs significantly influence AuNP electrodeposition. This study underscores the importance of systematically characterizing the electrodeposition parameters on novel electrode surfaces.