Monofunctionalized beta-cyclodextrins as sensor elements for the detectionof small molecules

beta -Cyclodextrins functionalized by different moieties that were tethered to a single 6-deoxyaminoglucose unit were investigated with respect to the ir suitability for sensor applications. Derivatizing the cyclodextrins with hydrophobic moieties like dipalmitoylglycerol and cholesterol allowed us t o study packing density and orientation of the cyclodextrin tori at the air -water interface. From the pressure-area isotherms, it was concluded that t he cyclodextrins are positioned towards the water subphase, with their mole cular axis predominately parallel to the interface. By introducing a disulf ide group, we managed to immobilize cyclodextrins on gold surfaces via self -assembly. MALDI mass spectrometry (MALDI MS) and XPS confirmed that the mo lecules are chemisorbed on the gold substrate displaying high surface cover age as determined by means of impedance spectroscopy. The inclusion of vari ous 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. (C) 2000 Elsevi er Science B.V. All rights reserved.