DISSERTATION

_____________________________________________________________ Results and Discussion
Figure 3.40. Comparison of the formation kinetics of MCU SAMs performed at a constant
potential equal to the previously measured OCP (0 V vs. Ag/AgCl/3 M KCl, black curve),
a constant potential of 0.5 V (grey curve) and by using the potential-assisted method with
a 0.5/-0.2 V potential-pulse profile with 10 ms pulse duration (orange curve).
Measurements were performed in 10 mM PB with 20 mM K2SO4 containing 1 mM MCU
(30 % ethanol). Inset: Immobilization kinetics of MCU at a potential equal to the OCP
shown for 12 h. Figure adapted from ref. 89 .
The obtained results for the kinetics of potential-assisted SAM formation suggest that the
stirring process generated by pulsing enhances both, the approach of thiol molecules towards
the electrified interface to allow formation of the Au-S bond and the packing and reorganization
of adsorbed molecules. It is important to understand that this process is not likely driven by
diffusion of thiols, but rather by migration of ions from the solution that carry along thiol
molecules towards the surface. Furthermore, a Langmuir isotherm cannot be used to fit our
experimental data, which supports the assumption that the process is not diffusion but rather
migration driven. The developed potential pulse-assisted SAM formation method is promising
for a fast and reproducible surface modification that may be implemented in diverse
applications especially related to the production of point-of-care devices.
3.3 Importance of controlling the surface 79