A significant broad band in the 3000 cm -1 to 3160 cm -1 range with a maximum at approx. 3050 cm -1 is found in the spectrum of aptamer-rich domains (figure ). Bands in this spectral region are specific for C-H stretching vibrations of aromatic rings (ν(C ar -H) and this band is found very weakly in the spectra of the protein and the PEG-rich phase.