DISSERTATION

_____________________________________________________________ Results and Discussion
Figure 3.39. CVs for the evaluation of blocking of the electrode surface. a) Before and
after MCU SAM formation using the potential-pulse assisted method. b) Rescaled CVs
obtained after different times of surface modification. 0.5/-0.2 V pulse profile with 10 ms
pulse duration was used. Immobilization was performed in 10 mM PB, 20 mM K2SO4
containing 1 mM MCU (30 % ethanol). CVs 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.
To evaluate how constant potentials influence the self-assembly of thiols with an –OH
functional group in aqueous solutions, a control experiment was performed by applying a
relatively high constant potential of 0.5 V (vs. Ag/AgCl/3 M KCl) during thiol chemisorption,
that is still below the potential range of Au-S bond cleavage. As can be seen in Figure 3.40, a
significant acceleration of the immobilization kinetics was observed as compared with the SAM
formation at OCP. However, the SAM formation kinetics is still substantially slower than the
observed kinetics obtained by the potential pulse-assisted immobilization method. A constant
capacitance value is reached after 3 h (Figure 3.40, grey curve), while with our approach
compact monolayers are obtained within only 5 min (Figure 3.40, orange curve). It should be
noted that, in contrast to the vast majority of reported procedures for electrochemical-assisted
thiol immobilization 13,21,22,92 , the proposed technique for SAM deposition is performed in
aqueous solutions ensuring high compatibility with biomolecules used for further surface
modification.
3.3 Importance of controlling the surface 78