Monofunctionalized β-cyclodextrins as sensor elements for the detection of small molecules

Abstract

β-Cyclodextrins functionalized by different moieties that were tethered to a single 6-deoxyaminoglucose unit were investigated with respect to their suitability for sensor applications. Derivatizing the cyclodextrins with hydrophobic moieties like dipalmitoylglycerol and cholesterol allowed us to study packing density and orientation of the cyclodextrin tori at the air–water interface. From the pressure-area isotherms, it was concluded that the cyclodextrins are positioned towards the water subphase, with their molecular axis predominately parallel to the interface. By introducing a disulfide group, we managed to immobilize cyclodextrins on gold surfaces via self-assembly. MALDI mass spectrometry (MALDI MS) and XPS confirmed that the molecules are chemisorbed on the gold substrate displaying high surface coverage as determined by means of impedance spectroscopy. The inclusion of various charged guest molecules was monitored by changes in the charge transfer resistance of the redox couple [Fe(CN) 6] 3−/[Fe(CN) 6] 4−. The charge transfer resistance is sensitive to the surface potential, which leads to either repulsion or attraction of the redox active species.