Competitive Attachment of Gold Nanoparticles on an Indium Tin Oxide Electrode.

Fundamental aspects of the attachment of gold nanoparticles (AuNPs) onto a 3-aminopropyltrimethoxysilane (APTMS) modified indium tin oxide (ITO) electrode were explored using commercially available Au colloid solutions of 5, 10 and 20 nm. In particular, competitive attachments of AuNPs were observed using mixed solutions of two Au colloids. Consequently, it was found that smaller AuNPs are easily attached on an APTMS modified ITO. On the other hand, the result of the stepwise attachments showed that after the surface was modified by the first AuNPs, the second AuNPs have difficulty attaching. This means, if surface connecting -NH2 terminals of APTMS are once occupied, further modification or exchange of the attached AuNPs would not be easy. From the present results, a contaminant amount of smaller AuNPs is considered to be a practical problem in modifying ITO surfaces by AuNPs.