Optical microscopy using a single-molecule light source

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 spatial(5) and spectral(6) detection of individual fluorescent molecules, using near-field and far-field methods(7), 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 spectroscopy(10) with shear-force microscopy(11). 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.