  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
micrometers 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. A nanoscale material characterization using
synchrotron IR radiation is discussed.
