Single-molecule near-field optical energy transfer microscopy

The nano-optical interaction between a sharp tip and a single dipolar emitter is investigated. Changes of the excited state lifetime and the fluorescence rate of single molecules are recorded simultaneously as a function of the tip position relative to the molecule. A subdiffraction-limited area of decreased fluorescence and shortened lifetime is observed for gold-coated Si3N4 tips. The results are discussed in terms of molecular fluorescence in a system of stratified media. The outlined methodology holds promise for applications in ultrahigh-resolution near-field optical imaging at the level of single fluorophores.