Bioinspired Amyloid Nanodots with Visible Fluorescence

Nanoscale bioimaging is a highly important scientific and technological tool, where fluorescent (FL) proteins, organic molecular dyes, inorganic quantum dots, and lately carbon dots are widely used as light emitting biolabels. In this work, a new class of visible FL bioorganic nanodots, self-assembled from short peptides of different composition and origin, is introduced. It is shown that the electronic energy spectrum of native nonfluorescent peptide nanodots (PNDs) is deeply modified upon thermally mediated refolding of their biological secondary structure from native metastable to stable beta-sheet rich structure. This refolding leads to the appearance of a broadband optical absorption across visible region and tunable, excitation-dependent visible FL of the nanodots with a high quantum yield of approximate to 30%. It is shown that this intriguing biophotonic effect appears in several peptides/proteins and does not require the presence of aromatic residues. It is assumed that the origin of the phenomenon is related to proton transfer along network of reconstructed intermolecular hydrogen bonds, stabilizing the thermally induced supramolecular beta-sheet structure. The biocompatible FL PNDs can be potentially applied as high-resolution bioimaging labels toward advanced biotechnology and biomedical theranostics.