To date, optical studies of single molecules at room temperature have relied on the use of materials with high fluorescence quantum yield combined with efficient spectral rejection of background light. To extend single-molecule studies to a much larger pallet of substances that absorb but do not fluoresce, scientists have explored the photothermal effect1, interferometry2,3, direct attenuation4 and stimulated emission5. Indeed, very recently, three groups have succeeded in achieving single-mo...