Influence of protective layers on the blinking of fluorescent single molecules observed by confocal microscopy and scanning near field optical microscopy

Abstract

Transitions of fluorescent Rhodamine 6G dye molecules into metastable dark states with lifetimes of several seconds were observed by single-molecule detection (SMD) using far-field confocal microscopy. The samples were protected with different organic thin films and were characterized using atomic force microscopy. The data are compared to published models: The best fit is found with a model suggesting that oxygen migration or polarity changes are responsible for the transitions. For further studies with molecules close to each other, we studied the capability of cantilever-SNOM sensors for SMD. Using an α-SNOM we were able to demonstrate 40 nm optical resolution of these new near-field tips for single-molecule fluorescence imaging in direct comparison with confocal microscopy on samples of Rhodamine 6G molecules protected by PMMA.