Single molecule detection and photochemistry on a surface using near-field optical excitation

We report the first photobleaching experiments of single molecules on a surface. Single molecules of rhodamine 6[ital G] are detected on a silica surface under ambient conditions using near-field scanning optical microscopy. Photobleaching of an individual molecule appears as an abrupt disappearance of fluorescence after seconds of constant excitation. Other reversible, upward and downward changes in fluorescence are observed, possibly due to reorientation of molecules on the surface.