Abstract

Recent progress in the fluorescence detection of individual molecules [1-8] suggests that a single dye molecule can be a useful tool to probe chemical identity and activity. Measurement of fluorescence lifetime [5,6] and spectrum [6] can be augmented by knowledge of molecular orientation using polarized light [3], and triplet [2] and photoisomer excitation, as well as diffusion processes, via fluorescence-intensity correlation. Applications of fluorescent probes include the study of the dynamic conformation of membrane-bound proteins, transport of and signaling by messenger molecules, and the optical detection of the sequence of DNA. While molecules can be spatially located using near-field microscopy [5-8], near-field probes can perturb the molecule under study. We show here that molecular properties can be determined easily and in a non-perturbative manner using far-field illumination, and we obtain unperturbed spectral and lifetime data that cannot be extracted from an ensemble measurement.

© 1996 Optical Society of America