A water soluble amorphous form of silk was made by ultra-short laser pulse irradiation and detected by nanoscale IR mapping. An optical absorption-induced nanoscale surface expansion was probed to yield the spectral response of silk at IR molecular fingerprinting wavelengths with a high ∼ 20 nm spatial resolution defined by the tip of the probe. Silk microtomed sections of 1-5 μm in thickness were prepared for nanoscale spectroscopy and a laser was used to induce amorphisation. Comparison of silk absorbance measurements carried out by table-top and synchrotron Fourier transform IR spectroscopy proved that chemical imaging obtained at high spatial resolution and specificity (able to discriminate between amorphous and crystalline silk) is reliably achieved by nanoscale IR. Differences in absorbance and spectral line-shapes of the bands are related to the different sensitivity of the applied methods to real and imaginary parts of permittivity. A nanoscale material characterization by combining synchrotron IR radiation and nano-IR is discussed.
JSPS KAKENHI Grant No.16K06768 Swinburne’s startup grant for Nanotechnology facility and partial support via ARC Discovery DP130101205 and DP170100131 grants beamtime project No. 11119 at the Australian Synchrotron IRM Beamline Window-on-Photonics R&D, Ltd. is acknowledged for joint development grant and laser fabrication facility
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