Photon Recycling Effect and Lossless Fluorescence Propagation in β-Sheet Peptide Fibers

Light-delivering optical fibers are widely used for biomedical imaging, theranostics and surgery, and optogenetics. In this work, a new generation of bioinspired optical fibers is proposed. Developed amyloidogenic peptide fibrillary structures with tailored beta-sheet conformation exhibit unique optical properties of full overlapping of broadband visible fluorescence (FL) and optical absorption spectra. This study reports on unexpected lossless propagation of the FL light along 100 mu m length beta-sheet microfibers. It is shown that the found FL long-distance lossless radiative energy transport occurs due to highly effective FL photon recycling phenomenon supported by FL zero Stokes shift and high quantum yield. This new non-Beer-Lambert FL lossless propagation mechanism is observed in very thin approximate to 1 mu m diameter fibers, providing a single/few-mode waveguiding regime. The developed model and computer simulations, based on the finite difference time domain method, are consistent with the experimental results. Fabricated peptide FL fiber probes permit delivering intensity-modulated FL signal with selected wavelength over the whole visible spectrum in wide modulation frequencies range.