Cyclic Voltammetric and Scanning Electrochemical Microscopic Study of Thiolated β-Cyclodextrin Adsorbed on a Gold Electrode

Abstract

Potassium ferricyanide ([Fe(CN)6]3-) reduction and ferrocenemethanol (Fc-OH) oxidation at a β-cyclodextrin (β-CD)-modified gold electrode were investigated by cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM) in phosphate buffer pH 7. CV and SECM experiments demonstrated that the surface of the modified electrode represents an insulating substrate for ferricyanide and a conductor substrate for Fc-OH. This difference is explained by the fact that Fc-OH can enter into the β-CD cavity forming an inclusion complex; on the other hand, ferricyanide is larger than the cavity of β-CD and so it cannot form an inclusion complex. Using the high sensitivity of the electron transfer of ferricyanide to the modification of the gold surface with β-CD, we selected this reaction as a probe to study the different modification stages at this modified electrode. When the electrode was partially modified, it was possible to obtain an adequate microscopic discrimination by using approach curves at different tip positions showing a nonhomogeneous surface. SECM images obtained from bare and partially and totally modified electrodes show very good resolution with different topography or null according to the extent of modification. When the modification was total, a homogeneous current with a regular topography was found, but when the modification was intermediate the topography was very irregular. To our knowledge, this is the first electrochemical study of a thiolated β-CD layer adsorbed on a gold electrode by SECM, and taken together, these results demonstrate that while the CV experiments give overall information about the studied surface, the SECM experiments permit microscopic characterization of the layer.

Self-assembled monolayers of a thiol-derivatized porphyrin on gold electrode: Film formation and electrocatalytic dioxygen reaction

“…Squella, in Bollo et al, once described that the coverage of a monolayer on electrode surface increased with the adsorption time [26], that is to say, the full monolayer coverage could be obtained when the adsorption time is long enough. As for the adsorption time, 24 h was chosen in this study for construction both MPTPPCo(II) and mixed SAMs, however, the maximum of the coverage gained under this circumstances is slightly lower than that expected for a close-packed edge-to-edge film of a similar cobalt porphyrin, 7.0 Â 10 À 11 mol/cm 2 [26]. This was also supported by AFM image in Fig.…”

Electrochemical Characterization of Self‐Assembled Thiol‐Porphyrin Monolayers on Gold Electrodes by SECM

“…These results are very similar to those reported for the cyclodextrin-SH modified electrode. [26] The rate constants A C H T U N G T R E N N U N G (k eff s) for ET across the monolayer are measured using Fe(CN) 6 3À as the mediator in solution. Table 1 shows a list of k eff values determined by SECM for different adsorption times.…”

Peptide Mesocrystals as Templates to Create an Au Surface with Stronger Surface‐Enhanced Raman Spectroscopic Properties

“…The cover degree is characterized . [32,[35][36][37] Using K 3 Fe(CN) 6 as active probe, B is calculated to be 0.1, which means that only part of the Au nanoflake surface is covered by 4-MBA molecules. Thus, the EF shown above is the lower limit and the actual value may be higher than 10 5 .…”