Towards the fluorescence resonance energy transfer (FRET) scanning near-field optical microscopy: Investigation of nanolocal FRET processes and FRET probe microscope

The fluorescence resonance energy transfer (FRET) process is investigated between donor dye molecules deposited on the sample surface and acceptor dye molecules deposited on the tips of scanning near-field and atomic force microscopes. The FRET process was observed only when the tip acquired contact with the sample and took place in regions of sizes of only a few tens of nanometers with only a few thousands (or even hundreds) of molecules involved. The dependence of the FRET intensity on the tip-sample acting force is recorded and interpreted. In relation with the obtained results, the construction of a previously proposed one - atom FRET SNOM is described.