Self-Assembled Monolayers of Monofunctionalized Cyclodextrins onto Gold:  A Mass Spectrometric Characterization and Impedance Analysis of Host−Guest Interaction

A novel β-cyclodextrin (β-CD) functionalized by a mercaptopropionic acid that was attached to a single 6-deoxyaminoglucose unit has been synthesized in the disulfide form. The flexible single-thiol spacer allows the formation of a monomolecular film by self-assembly onto gold, yielding a high packing density with a surface coverage of 99.6% and a capacitance of 9 μF/cm2, determined by impedance spectroscopy. MALDI-MS and XPS analysis clearly showed that the modified cyclodextrin is chemisorbed on the gold surface by Au−S bonds. Addition of 3-mercaptopropionic acid to the preformed β-CD monolayer considerably improved the intensity of the MALDI mass spectra signals. The incorporation of anilinonaphthalenesulfonates into the β-CD cavity was observable by impedance spectroscopy using the electroactive markers [Fe(CN)6]3-/[Fe(CN)6]4-.