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. 2016 Oct 7;7:13079. doi: 10.1038/ncomms13079

Figure 3. Quantitative evaluation of conformational transitions in silk proteins using near-field IR nano-spectroscopy.

Figure 3

(a) Schematics of IR nano-spectroscopy using AFM–IR: pulses of IR radiation emitted by an IR QCL (output range: 1,460–1,780 cm−1, swept by a step size: 1 cm−1) were used to illuminate the sample, causing a rapid thermal expansion of silk nanostructures due to local absorption enhancement at various stages picked by the AFM tip, corresponding to the absorption spectroscopic signatures. (b,c) The AFM–IR spectra on amorphous and crystalline silk thin films are consistent with the conventional bulk FTIR spectra. (d,e) 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. (f) 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.