Light waveguiding in bioinspired peptide nanostructures

A Comprehensive Analysis of the Intrinsic Visible Fluorescence Emitted by Peptide/Protein Amyloid-like Assemblies

Amyloid aggregation is a widespread process that involves proteins and peptides with different molecular complexity and amino acid composition. The structural motif (cross-β) underlying this supramolecular organization generates aggregates endowed with special mechanical and spectroscopic properties with huge implications in biomedical and technological fields, including emerging precision medicine. The puzzling ability of these assemblies to emit intrinsic and label-free fluorescence in regions of the electromagnetic spectrum, such as visible and even infrared, usually considered to be forbidden in the polypeptide chain, has attracted interest for its many implications in both basic and applied science. Despite the interest in this phenomenon, the physical basis of its origin is still poorly understood. To gain a global view of the available information on this phenomenon, we here provide an exhaustive survey of the current literature in which original data on this fluorescence have been reported. The emitting systems have been classified in terms of their molecular complexity, amino acid composition, and physical state. Information about the wavelength of the radiation used for the excitation as well as the emission range/peak has also been retrieved. The data collected here provide a picture of the complexity of this multifaceted phenomenon that could be helpful for future studies aimed at defining its structural and electronic basis and/or stimulating new applications.

Biophotonic probes for bio-detection and imaging

The rapid development of biophotonics and biomedical sciences makes a high demand on photonic structures to be interfaced with biological systems that are capable of manipulating light at small scales for sensitive detection of biological signals and precise imaging of cellular structures. However, conventional photonic structures based on artificial materials (either inorganic or toxic organic) inevitably show incompatibility and invasiveness when interfacing with biological systems. The design of biophotonic probes from the abundant natural materials, particularly biological entities such as virus, cells and tissues, with the capability of multifunctional light manipulation at target sites greatly increases the biocompatibility and minimizes the invasiveness to biological microenvironment. In this review, advances in biophotonic probes for bio-detection and imaging are reviewed. We emphatically and systematically describe biological entities-based photonic probes that offer appropriate optical properties, biocompatibility, and biodegradability with different optical functions from light generation, to light transportation and light modulation. Three representative biophotonic probes, i.e., biological lasers, cell-based biophotonic waveguides and bio-microlenses, are reviewed with applications for bio-detection and imaging. Finally, perspectives on future opportunities and potential improvements of biophotonic probes are also provided.

Amyloid-like Prep1 peptides exhibit reversible blue-green-red fluorescence in vitro and in living cells

PREP1-based peptides form amyloid-like aggregates endowed with an intrinsic blue-green-red fluorescence with an unusual sharp maximum at 520 nm upon excitation with visible light under physiological conditions. The peptide PREP1[117-132], whose sequence does not contain aromatic residues, presents a pH-dependent and reversible fluorescence, in line with its structural transition from β-sheet rich aggregates to α-helix structures. These findings further demonstrate that the non-canonical fluorescence exhibited by amyloids is an articulated phenomenon.