Time-resolved studies of energy transfer in thin films of green and red fluorescent proteins

Biologically derived fluorescent proteins are attractive candidates for lasing and sensing due to their excellent optical properties, including their high quantum yield, spectral tunability and robustness against concentration quenching. Here, we report a time-resolved study of the fluorescence dynamics of thin films of Enhanced Green Fluorescent Protein (EGFP), the red-emitting tandem-dimer protein tdTomato and blends of EGFP and tdTomato. We characterized the exciton dynamics by using spectrally and time-resolved measurements of fluorescence and observed a threefold reduction in lifetime when going from solution to thin film, down to 1 ns and 0.6 ns for EGFP and tdTomato, respectively. This finding is attributed to a dipole-dipole non-radiative Förster resonant energy transfer (FRET) in solid-state. We also studied the temporal characteristics of FRET in blended thin films and found increased non-radiative transfer rates. Finally, we report efficient sensitisation of a semiconductor surface with a protein thin film. Such a configuration may have important implications for energy harvesting in hybrid organic-inorganic solar cells and other hybrid optoelectronic devices.