Benzenesulfonamidoquinolino-beta-cyclodextrin as a cell-impermeable fluorescent sensor for Zn2+

A water-soluble benzenesulfonamidoquinolino-beta-cyclodextrin has been successfully synthesized in 30% yield by incorporating a N-(8-quinolyl)-p-aminobenzenesulfonamide (HQAS) group to beta-cyclodextrin through a flexible linker. This compound exhibits a good fluorescence response in the presence of Zn2+ in water but gives poor fluorescence responses with other metal ions commonly present in a physiological environment under similar conditions. Fluorescence microscopic and two-dimensional NMR experiments showed that benzenesulfonamidoquinolino-beta-cyclodextrin could bind to the loose bilayer membranes. As a result, benzenesulfonamidoquinolino-beta-cyclodextrin was found to act as an efficient cell-impermeable Zn2+ probe, showing a specific fluorescent sensing ability to Zn2+-containing damaged cells whilst exhibiting no response in the presence of healthy cells.