Investigating the transverse optical structure of spider silk micro-fibers using quantitative optical microscopy

Nanophotonics

article

Douglas J. Little¹  Deb M. Kane¹ 

[1] MQ Photonics Research Centre, Department of Physics and Astronomy, Macquarie University

关键词: spider silk;    micro-fibers;    refractive index;    quantitative microscopy;    optical scattering;   

DOI  :  10.1515/nanoph-2016-0125

学科分类：社会科学、人文和艺术（综合）

来源: De Gruyter

【 摘 要 】

The transverse optical structure of two orb-weaver (family Araneidae ) spider dragline silks was investigated using a variant of the inverse-scattering technique. Immersing the silks in a closely refractive index-matched liquid, the minimum achievable image contrast was greater than expected for an optically homogeneous silk, given what is currently known about the optical absorption of these silks. This “excess contrast” indicated the presence of transverse optical structure within the spider silk. Applying electromagnetic scattering theory to a transparent double cylinder, the minimum achievable irradiance contrast for the Plebs eburnus and Argiope keyserlingi dragline silks was determined to be consistent with step index refractive index contrasts of 1−4×10 −4 and 6–7×10 −4 , respectively, supposing outer-layer thicknesses consistent with previous TEM studies (50 nm and 100 nm, respectively). The possibility of graded index refractive index contrasts within the spider silks is also discussed. This is the strongest evidence, to date, that there is a refractive index contrast associated with the layered morphology of spider silks and/or variation of proportion of nanocrystalline components within the spider silk structure. The method is more generally applicable to optical micro-fibers, including those with refractive index variations on a sub-wavelength scale.

【 授权许可】

CC BY