Förster resonance energy transfer photoacoustic microscopy.

Förster, or fluorescence, resonance energy transfer (FRET) provides fluorescence signals sensitive to intra- and inter-molecular distances in the 1 to 10 nm range. Widely applied in the fluorescence imaging environment, FRET enables visualization of physicochemical processes in molecular interactions and conformations. In this paper, we report photoacoustic imaging of FRET, based on nonradiative decay that produces heat and subsequent acoustic waves. Estimates of the energy transfer efficiency by photoacoustic microscopy were compared to those obtained by fluorescence confocal microscopy. The experimental results in tissue phantoms show that photoacoustic microscopy is capable of FRET imaging with an enhanced penetration depth. Through its ability to three-dimensionally image tissue with scalable resolution, photoacoustic microscopy could be a beneficial biomedical tool to broaden the in vivo application of FRET.