Applications brief: Nanoscale probing of electron-regulated structural transitions in silk proteins by near-field IR imaging and nano-spectroscopy

Key points


  • AFM-IR and s-SNOM have been used in combination to probe the protein secondary structure changes of silk proteins induced by electron beam exposure.
  • Due to the direct correlation of AFM-IR with conventional infrared spectroscopy, protein secondary structure analysis can now be extended to the nanoscale.
  • High resolution s-SNOM imaging is used to illustrate the structural changes in the silk protein caused by electron beam lithography.
  • The understanding of these nanoscale structural changes induced by electron beam exposure will allow for the development of advanced 2D and 3D biomaterials.

Key words

AFM-IR | s-SNOM | Silk Protein | Protein Secondary Structure | Structural Changes | Lithography

Authors

N. Qin, S. Zhang, J. Jiang, S.G. Corder, Z. Qian, Z. Zhou, W. Lee, K. Liu, X. Wang, X. Li, Z. Shi, Y. Mao, H. A. Bechtel, M. Martin, X. Xia, B. Marelli, D. L. Kaplan, F. Omentto, M. Liu, T.H. Tao

Abstract

Silk protein fibres produced by silkworms and spiders are renowned for their unparalleled mechanical strength and extensibility arising from their high-b-sheet crystal contents as natural materials. Investigation of b-sheet-oriented conformational transitions in silk proteins at the nanoscale remains a challenge using conventional imaging techniques given their limitations in chemical sensitivity or limited spatial resolution.

Here, we report on electron regulated nanoscale polymorphic transitions in silk proteins revealed by near-field infrared imaging and nano-spectroscopy at resolutions approaching the molecular level. The ability to locally probe nanoscale protein structural transitions combined with nanometre-precision electron-beam lithography offers us the capability to finely control the structure of silk proteins in two and three dimensions.

Our work paves the way for unlocking essential nanoscopic protein structures and critical conditions for electron-induced conformational transitions, offering new rules to design protein-based nanoarchitectures.

Image: AFM-IR spectra of electron-induced structural transitions in silk proteins. PSD, position sensing detectors; PZT, lead zirconate titanate (Pb[ZrxTi1-x]O3); EC- QCL, external cavity quantum cascade laser.

Spectra of a crystalline silk thin film with embedded amorphous silk nanopatterns of ∼30 nm fabricated using EBL, characterized by attenuated total reflection IR (ATR-IR) and AFM-IR, respectively. AFM-IR offers a considerable advancement ( × ∼1,000improvement spatially) in distinguishing nanoscale structural heterogeneity.

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