1. Fachbereich Physik and Optik-Zentrum Konstanz, Universität Konstanz, Fach M696, 78457 Konstanz, Germany

Correspondence to: V. Sandoghdar Correspondence and requests for materials should be addressed to V.S. (e-mail: Email: vahid.sandoghdar@uni-konstanz.de).

Abstract

Rapid progress in science on nanoscopic scales has promoted increasing interest in techniques of ultrahigh-resolution optical microscopy. The diffraction limit can be surpassed by illuminating an object in the near field through a sub-wavelength aperture at the end of a sharp metallic probe^{1, 2}. Proposed modifications^{3, 4} of this technique involve replacing the physical aperture by a nanoscopic active light source. Advances in the spatial⁵ and spectral⁶ detection of individual fluorescent molecules, using near-field and far-field methods⁷, suggest the possibility of using a single molecule^{8, 9} as the illumination source. Here we present optical images taken with a single molecule as a point-like source of illumination, by combining fluorescence excitation spectroscopy¹⁰ with shear-force microscopy¹¹. Our single-molecule probe has potential for achieving molecular resolution in optical microscopy; it should also facilitate controlled studies of nanometre-scale phenomena (such as resonant energy transfer) with improved lateral and axial spatial resolution.