Characteristic spectral features that can be assigned specifically to the protein lie in the range from 1520 cm -1 to 1710 cm -1 (cf. table ). Compared to the spectra of the receptor layer, the protein spectra show a slight increase in intensity from 1520 cm -1 to 1560 cm -1 and a notably strong increase in intensity from 1600 cm -1 to 1710 cm It is interesting to compare the structural properties of the surface bound protein to the solution structure. To that end, an ATR-IR spectrum of the protein in solution was recorded. The comparison with the nano-IR difference spectrum of the adsorbed proteins shows that the latter is significantly shifted to higher frequencies (figure ). The S proteins in solution have the Amide I maximum at approx. 1635 cm -1 while the adsorbed protein is centered clearly above 1650 cm -1 (exact value 1665). This shift indicates that the secondary structure of the surface-bound S protein is significantly altered as compared to the solution structure. This goes in hand with the observed relatively low height of the protein in the AFM topography compared to its solution structure. The S protein is known to be a trimer with major axes dimensions of approx. 10 nm and 15 nm. The found heights of approx.