Immobilization and surface functionalization of gold nanoparticles monitored via streaming current/potential measurements.

A streaming current/potential method is optimized and used for the analysis of the variation of the surface potential upon chemical modifications of a complex interface consisting of different organic molecules and gold nanoparticles (AuNPs). The surfaces of Si/SiO2 substrates modified with 3-aminopropyltriethoxysilane (APTES), AuNPs, and 11-amino-1-undecanethiol (aminothiols) are analyzed via pH and time dependent ζ potential measurements that reveal the stability and modification of the surface and identify crucial parameters for each individual preparation step. For instance, surface activation and especially molecular adsorbate layers tend not to be stable in time, whereas the substrate and the AuNPs provide a stable surface potential as long as impurities are avoided. It is shown that the streaming potential/current technique represents an ideal tool to analyze and monitor the complex surfaces and their modification.