Self-assembled monolayers of monofunctionalized cyclodextrins onto gold: A mass spectrometric characterization and impedance analysis of host-guest interaction

A novel beta-cyclodextrin (beta-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 mu F/cm(2), 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 beta-CD monolayer considerably improved the intensity of the MALDI mass spectra signals. The incorporation of anilinonaphthalenesulfonates into the beta-CD cavity was observable by impedance spectroscopy using the electroactive markers [Fe(CN)(6)](3-)/[Fe(CN)(6)](4-).