Bioinspired Amyloid Nanodots with Visible Fluorescence

Abstract

mostly based on fluorescent (FL) agents of high brightness and combines exceptional optical properties with biocompatibility, biodegradability, and precise targeting both in vivo and in vitro. This includes inorganic semiconductor quantum dots, [2] carbon nanodots, [3] organic molecular dyes, [4] and genetically encoded universal FL proteins. [5] Additional specific class of extrinsic FL nanoprobes is amyloidbinding small molecule ligands (thioflavin T, Congo red and more) employed for tracking the kinetics of amyloid fibrils growth. [6] Each of the imaging agents has its inherent mechanism of photon emission, which defines its figures of merit for bioimaging: FL spectral region, quantum yield (QY), and photobleaching. [7,8] For instance, quantum dots and organic dye molecules exhibit FL in the visible range and have very high QY exceeding 90%. However, the organic molecular dyes are limited for long-term bioimaging applications because of photobleaching issues. The biocompatibility is another basic parameter of any biolabels, which is especially critical for some organic dyes and inorganic semiconductor quantum dots, containing heavy metals. Recently found FL carbon nanodots are biocompatible but have a low QY. [9] The green fluorescence protein (GFP) and its homologues are the only molecules, known until today, having biological origin FL and providing unique biocompatibility. These proteins exhibit pronounced FL with QY reaching 90% covering the entire visible spectrum, which makes them unique FL tags [10] among unlimited number of nonfluorescent peptide and protein biomolecules. [1,2,5,7] Alternative composition-insensitive visible FL was recently found in biological and bioinspired nanostructures characterized by specific ordering of biomolecules into antiparallel β-sheets structures. This includes a wide variety of diverse biomolecular compositions, such as amyloidogenic proteins, [11,12] PEGylated peptides, [13,14] nonaromatic biogenic, and synthetic peptides [15] and recently natural silk fibrils. [16] The basic features of these FL nanostructures are similar fibrillar morphology, original β-sheets secondary structure, and identical visible FL optical spectrum. These common structural and optical properties enable to relate all of them to a wide class of thermodynamically stable disease-and nondiseased-related amyloid structures. [17][18][19] Such β-sheet structures and visible FL can also 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 β-sheet rich structure. This ...

Long‐Range Fluorescence Propagation in Amyloidogenic β‐Sheet Films and Fibers

“…The effect of the visible FL found in many biological and bioinspired nanomaterials of different origin and composition is ascribed to their β‐sheet peptide/protein secondary structures. [ 9–15,17,45 ] This biophotonic FL phenomenon is characterized by a maximum FL intensity in the blue region at 450–460 nm. Apart from the blue FL observed in PEG 12 ‐F6 and PEG 18 ‐F6 fibers, PEG 24 ‐F6 exhibited an additional FL radiation in the green optical region (λ = 520 nm).…”

“…The amyloidogenic structures under study exhibit exclusive broadband, fully overlapped FL and OA spectra (Figure 1 and 3), which are created by the electronic structure of noncovalent hydrogen bonds responsible for visible FL in amyloid structures. [ 9–12,14–17 ] FL and OA effects are detected along the entire visible spectrum in the 400–650 nm range. This effect provides the observation of any FL visible color, blue, green, yellow, red, and more.…”

“…This intrinsic, structure‐sensitive bio‐effect has been observed in a variety of β‐sheet disease‐related human peptide amyloid fibrils, [ 10,11 ] native silk fibrils, [ 12 ] synthetic vapor‐deposited diphenylalanine (FF)‐fibers, [ 13 ] bioinspired thermally refolded diaromatic and triaromatic and aliphatic peptide nanostructures, [ 9,14 ] and recently in peptide/protein nanodots. [ 15,16 ] Regardless of their composition and origin, they irradiate FL in a similar visible range within a wide spectral maximum in the blue region. Recently, a deep study of amyloid fibrils involving 13 different amyloid proteins showed that, in addition to its blue component, the amyloid FL signal also contains a red near‐infrared FL spectral component with wavelengths of 780–820 nm.…”

“…The latter folds into a peptide β‐sheet structure and exhibits a new phenomenon of quasi‐white visible FL, in which PEG‐polymer chains contribute to wideband green FL [ 43–45 ] in addition to the blue FL found in diverse beta‐sheet disease‐related human peptide/protein amyloid fibrils, native silk fibrils, vapor‐deposited diphenylalanine fibers, and recently in peptide/protein nanodots. [ 9–17 ] The PEG‐6 peptide films have a very large area, making these unique peptide films promising for complex peptide integrated photonic devices. We demonstrate in these films effective optical passive FL waveguiding in fabricated simple photonic circuits.…”

Study of Electron-Vibrational Interaction in Molecular Aggregates Using Mean-Field Theory: From Exciton Absorption and Luminescence to Exciton-Polariton Dispersion in Nanofibers

“…We emphasize that factorization adopted in Eq. (14) corresponded to neglect of all correlations among different molecules. 28 At the same time the factorization corresponds to a random phase approximation 39 that enables us to split the term (n m1 − n m2 )b n into the product of populations and polarization ( b n ).…”