Continuum xl

Synchrotron Radiation FTIR microspectroscopy (SR-microFTIR) was performed at the SMIS beamline of SOLEIL Synchrotron facility (Saint-Aubin, France). Lyz-AuNPs samples for SR-microFTIR measurements were separated from non-adsorbed lysozyme by centrifugation, deposited by drop-casting procedure onto a double-polished silicon substrate and dried at room temperature. IR spectra of selected areas were measured in transmission with a Continuum XL (Thermo Fisher Scientific) IR microscope equipped with a liquid nitrogen cooled MCT detector, a 32× Schwarzschild objective, a motorized aperture and stage. The microscope was coupled to a Nicolet 5700 FTIR spectrometer (Thermo Fisher Scientific). We used an aperture of 8 μm × 8 μm, a spectral resolution of 4 cm - 1 and 200 scans for each acquisition. A background spectrum was collected for every batch of spectra through a clean area of the silicon substrate. Spectra reported in the present paper are the average of at least 5 acquisitions and are presented after baseline subtraction, smoothing procedure by the Savitzky-Golay algorithm (2 nd order polynomial, 8 data points) and normalisation to the maximum absorbance value. Spectral analysis was performed using Origin 8.1 software.