A Self-Assembled Sensor for Carbohydrates on the Surface of Cyclodextrin Vesicles

A supramolecular carbohydrate sensor was prepared by self-assembly of unilamellar bilayer vesicles of amphiphilic -cyclodextrin with a boronic acid-adamantane conjugate (PBA-AD), which binds strongly to -cyclodextrin through host-guest interactions (K-a approximate to 4x10(4)m(-1)), so the vesicle surface exhibits multiple boronic acid receptors for carbohydrates. The binding of diols to the functionalized vesicles was tested with alizarin redS (ARS) as a reporter dye by using fluorescence and UV/Vis spectroscopy. Analysis of the competitive binding of monosaccharides revealed pH-dependent (pH7.4-10.1) binding constants in the range of 100-3000m(-1) for d-fructose and 5-400m(-1) for d-glucose. Interestingly, the self-assembled sensor showed fluorescence intensity enhanced by about fivefold and a binding affinity to the reporter dye increased by about eightfold in comparison to PBA-AD and ARS without vesicles. This is attributed to increased local concentration of ARS and PBA-AD on the surface of the vesicles. Detection of d-fructose and d-glucose was possible in the physiologically relevant range in dilute aqueous solution.