Near-Field Scanning Optical Microscopy of Single Fluorescent Dendritic Molecules

Individual dendritic molecules adsorbed on glass containing a single fluorescent rhodamine B core have been observed with near-field scanning optical microscopy (NSOM); height and fluorescence images were obtained simultaneously. The dendritic assemblies can be discriminated from free fluorescent cores on the basis of accurate simultaneous localization of both the fluorescent core and the surrounding dendritic shell. There are no significant differences between the photophysical properties of the free and dendritic fluorophores. The full three-dimensional orientation of each individual fluorescent core can be resolved and millisecond time resolution accuracy has been achieved. Most dendritic structures exhibited rotational motion of the fluorescent core on a millisecond−second time scale, revealing intramolecular conformational dynamics.