Imaging of localized enzymatic peroxidase activity over unbiased individual gold nanowires by scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) in the constant-height mode was used to image individual gold nanowires (AuNWs, 2-3 mu m long and similar to 140 nm diameter). High-resolution negative and positive feedback current images of individual AuNWs immobilized on glass and gold-coated glass slides, respectively, were recorded with a Wollaston-based platinum disk ultramicroelectrode (UME) of radius 300 nm at 0.3 V probe potential using ferrocenemethanol as the mediator. The negative and positive feedback current responses were dependent on the effective recycling of the mediator on the unbiased AuNWs. Furthermore, the AuNWs were covalently linked to horseradish peroxidase (HRP) and immobilized on a thin film gold substrate. Positive feedback and localized HRP activity over individual AuNWs were imaged subsequently by switching the probe potential from 0.3 V to 0 V after the addition of H2O2. In this measurement, ferrocenemethanol behaved both as the mediator (feedback response at 0.3 V probe potential) and the electron donor for HRP (in the presence of H2O2 for activity imaging at 0 V).