Photoluminescent peptide based nanostructures as FRET donor for fluorophore dye

A great interest has been recently generated by the discovery that peptide-based nanostructures (NSs) endowed with cross-beta structure may show interesting photoluminescent (PL) properties. In this scenario, we have shown that NSs formed by PEGylated hexaphenylalanine (PEG8-F6) are able to emit at 460 nm when excited at 370 or at 410 nm. Here, we explored the possibility to transfer the fluorescence of these PEG8-F6-based NSs by Foster Resonance Electron Transfer (FRET) phenomenon to a fluorescent dye. To achieve this aim, we encapsulated in these NSs the 4-Chloro-7-nitrobenzofurazan (NBD) dye. Structural data, obtained by a variety of techniques (CD, FTIR, WAXS and SAXS), indicate that the organization of the peptide spine of PEG8-F6 NS, which consists of anti-parallel beta-sheets separated by a dry interface made of interacting phenylalanine side chains, is maintained upon NBD encapsulation. The spectroscopic characterization of these NSs clearly unravels a red-shift of the emission fluorescence peak both in solution and in solid state. This shift from 460 to 530 nm indicates that a FRET phenomenon from the peptide-based to the fluorophore-encapsulated NS occurs. Interestingly, we also show that FRET can also be detected in the PEG8-F6 conjugate in which the NBD is covalently bound to the amine of the compound. On the basis of the present results, we suggest that the red-shift of the intrinsic PL of NSs may be concretely exploited in the bioimaging field.

Photoluminescent peptide based nanostructures as FRET donor for fluorophore dye

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