DISSERTATION

_____________________________________________________________ Results and Discussion
Figure 3.42. Recycling treatment of an Au electrode. Three cycles of surface modification
with a MCU SAM and subsequent desorption are shown. a) bare electrode; b) after 1 min
of potential-pulse assisted SAM formation (0.5/-0.2 V vs. Ag/AgCl/3 M KCl, 10 ms); c)
after 30 s potential-pulse desorption (0.9/-0.9 V vs. Ag/AgCl/3 M KCl, 10 ms); d) after
SAM formation; e) after desorption (30 s); f) after SAM formation; g) after desorption (5
s). Measurements were performed in 10 mM PB, 20 mM K2SO4 containing 5 mM of
K3[Fe(CN)6] and K4[Fe(CN)6] at 100 mV/s scan rate.
Furthermore, to investigate whether the developed method can desorb also highly compact
SAM layers, desorption of MCU SAMs was investigated (Figure 3.42 and Figure 3.43). A MCU
SAM was formed by the potential-pulse assisted method (0.5/-0.2 V, 10 ms pulse duration, total
time 1 min) leading to a full blocking of electron transfer from the free-diffusing redox mediator
(Figure 3.42, a and b). Then, potential-pulse assisted desorption was performed for 30 s
resulting in a complete regeneration of the gold surface (Figure 3.42, c), showing that the
employed desorption procedure efficiently removes also compact thiol layers from the electrode
surface. To verify whether the electrode surface remains undamaged after the used desorption
procedure, immobilization/desorption cycles were repeated 3 times on the same electrode. The
passivation of the surface by the MCU SAM is very reproducible and the surface becomes fully
blocked (Figure 3.43, a). By using the developed desorption method the surface gets fully
regenerated after each cycle (Figure 3.43, b), which proves that the employed desorption
approach is harmless for the Au surface. Finally, the first two desorption cycles were performed
3.3 Importance of controlling the surface 83