Biophotonics of Native Silk Fibrils

Abstract

is produced in multiple unrelated organ isms, [3] ranging from ants to spiders, with one of the most prevalent examples being the silkworm Bombyx mori (B. mori). The B. mori silkworm spins fibers from a precursor solution of liquid silk pro tein, stored in the animal's silk gland, and uses them to form a nonwoven composite cocoon protecting the animal during its further metamorphosis. [4] The silk fiber formation process exerts shear and elon gation stresses on a concentrated solu tion containing fibroin (up to 30% wt/vol) in the gland, causing soluble fibroin to denature and aggregate. [5] Many studies have been conducted on different types of silk, including the characterization of the structural nature of fibroin, [6,7] the aggre gation and fiber formation pathway, [8] as well as the mechanical and rheological properties of silk solutions and fibers. [9][10][11] These studies have shown that the mole cular architecture of fibrous silk assemblies and the associated irreversible aggregation processes are similar to those found for highly ordered amyloid fibrils. [12][13][14] As functional materials, silk fibroin (SF) fibers are of particular interest because of their Native Silk Fibrils Native silk fibroin (NSF) is a unique biomaterial with extraordinary mechanical and biochemical properties. These key characteristics are directly associated with the physical transformation of unstructured, soluble NSF into highly organized nano-and microscale fibrils rich in β-sheet content. Here, it is shown that this NSF fibrillation process is accompanied by the development of intrinsic fluorescence in the visible range, upon near-UV excitation, a phenomenon that has not been investigated in detail to date. Here, the optical and fluorescence characteristics of NSF fibrils are probed and a route for potential applications in the field of self-assembled optically active biomaterials and systems is explored.In particular, it is demonstrated that NSF can be structured into autofluorescent microcapsules with a controllable level of β-sheet content and fluorescence properties. Furthermore, a facile and efficient fabrication route that permits arbitrary patterns of NSF microcapsules to be deposited on substrates under ambient conditions is shown. The resulting fluorescent NSF patterns display a high level of photostability. These results demonstrate the potential of using native silk as a new class of biocompatible photonic material.

Silk Fibroin‐Based Films Enhance Rhodamine 6G Emission in the Solid State: A Chemical–Physical Analysis of their Interactions for the Design of Highly Emissive Biomaterials

“…Tyr emission is observed at 302 nm for all the films while the RHD emission maxima shift from 558 to 594 nm upon increasing the RHD content. An additional blue fluorescence at 420–450 nm, already reported in the literature, and more evident by exciting at 300 or 407 nm (Figure b and Figure S5, Supporting Information), is observed in all the films. It has been shown that crosslink formation in SF solutions induces a broad emission in the 390–407 nm region, that is significantly enhanced and red‐shifted in the blue region in gels .…”

Peptide Nanophotonics: From Optical Waveguiding to Precise Medicine and Multifunctional Biochips

“…Unlike active waveguiding in dyes‐doped organic and bio‐organic structures this new biophotonic broadband visible FL effect does not involve an incorporation of foreign fluorescent dyes into original peptide material. The visible FL appears due to reconformation of peptide secondary structure from native state to β‐sheet and is ascribed to the network of hydrogen bonds of this basic peptide/protein organization (Figure ).…”

“…Found in ultrashort di-and tripeptide nanofibers visible FL effect has the same physical origin as FL effect revealed in PEGylated peptide PEG-F6 and its derivatives, [116,117] nonaromatic biogenic and synthetic peptides, [118] amyloid fibrils [119,120] and recently in natural silk fibrils. [121] This biophotonic effect is considered as an optical signature of β-sheet peptide secondary biological structures (Figure 3p-r). It is ascribed to noncovalent hydrogen bonds interconnecting the β-strands into β-sheet structure and creating a dense network of intrinsic visible fluorescent dyes.…”

“…The visible FL appears due to reconformation of peptide secondary structure from native state to β-sheet and is ascribed to the network of hydrogen bonds of this basic peptide/protein organization [18,53,[119][120][121] (Figure 3).…”

Light waveguiding in bioinspired peptide nanostructures

“…Figure F to H demonstrates blue and green FL from β‐sheet FFF nanospheres and FFF nanoplates excited by 360 and 410‐nm light, respectively. Found in ultrashort dipeptide and tripeptide nanofibers, visible FL effect has the similar physical origin as FL effect revealed in PEGylated peptide (PEG‐F6) and its derivatives, nonaromatic biogenic and synthetic peptides, amyloid fibrils, and native silk fibrils . This common biophotonic phenomenon is considered as an optical signature of β‐sheet peptide/protein biological secondary structure .…”