Identification and classification of silks using infrared spectroscopy

Abstract

Lepidopteran silks number in the thousands and display a vast diversity of structures, properties and industrial potential. To map this remarkable biochemical diversity, we present an identification and screening method based on the infrared spectra of native silk feedstock and cocoons. Multivariate analysis of over 1214 infrared spectra obtained from 35 species allowed us to group silks into distinct hierarchies and a classification that agrees well with current phylogenetic data and taxonomies. This approach also provides information on the relative content of sericin, calcium oxalate, phenolic compounds, poly-alanine and poly(alanine-glycine) β-sheets. It emerged that the domesticated mulberry silkmoth Bombyx mori represents an outlier compared with other silkmoth taxa in terms of spectral properties. Interestingly, Epiphora bauhiniae was found to contain the highest amount of β-sheets reported to date for any wild silkmoth. We conclude that our approach provides a new route to determine cocoon chemical composition and in turn a novel, biological as well as material, classification of silks.

Silk: Optical Properties over 12.6 Octaves THz-IR-Visible-UV Range

“…Fibroin based fibers have been extensively studied in this wavelength region [41,42]; therefore, measurements provide a way for verification against the established body of work. Figure 5 shows cross polarised images of the samples.…”

“…The N–H stretching, alkyl, and Amide bands represent the most prominent spectral features for all three samples. Some absorbance peaks of significant interest are the 961 cm${}^{-1}$ band attributed to poly-alanine (Ala)${}_n$ in $\beta$-sheets, observed primarily in wild silks [41]. Conversely, domesticated B. mori derived white silk fibers exhibit different, slightly subdued features at 975 and 998 cm${}^{-1}$, consistent with their (Ala-Gly)${}_n$ based $\beta$-sheets [41,43].…”

“…Some absorbance peaks of significant interest are the 961 cm${}^{-1}$ band attributed to poly-alanine (Ala)${}_n$ in $\beta$-sheets, observed primarily in wild silks [41]. Conversely, domesticated B. mori derived white silk fibers exhibit different, slightly subdued features at 975 and 998 cm${}^{-1}$, consistent with their (Ala-Gly)${}_n$ based $\beta$-sheets [41,43]. The component at 1014 cm${}^{-1}$ is associated with random coil (Ala-Gly) sequences that have many interruptions by tyrosine (Tyr), valine (Val) or other peptide chains [43], and, as expected, it is most pronounced in the spectrum of disordered amorphous fibroin.…”

Silk Fibroin Nanoparticles for Drug Delivery: Effect of Bovine Serum Albumin and Magnetic Nanoparticles Addition on Drug Encapsulation and Release

“…In addition, propranolol exhibited characteristic peaks in sharp absorption bands at 1680-1620 cm −1 (C=C stretching) and 1260-1000 cm −1 (C-O stretching) [28]. On the contrary, the FTIR spectrum of pramipexole-encapsulated fibroin nanoparticles presented no difference compared to pure fibroin nanoparticles; the characteristic peaks of pramipexol were not evident, leading to the conclusion that after encapsulation with pramipexole the chemical bonding remained unchanged [29]. The assignments of the FTIR bands of silk fibroin nanoparticles as well as those of the drug-encapsulated silk fibroin nanoparticles are presented in detail in Table 4.…”

Silk patterns made by direct femtosecond laser writing

“…20 The discrete shoulder in the vicinity of 1676 cm À1 is associated with the bends and turns of the polypeptide chain. 21,22 Laser irradiation of the amorphous silk fibroin diminishes the intensity of amide bands and at the same time induces spectral alternations at 1660 and 1543 cm À1 wavenumbers, associated with the a-helix conformation.…”