Near edge X-ray absorption fine structure spectroscopy(NEXAFS) and synchrotron radiation photoelectron spectroscopy(SRPES) were employed to investigate the adsorption mechanism of tryptophan(Trp) onto single-walled carbon nanotubes(SWCNTs).The difference of the carbon K-edge NEXAFS spectra between Trp molecules and Trp-adsorbed SWCNTs shows that a significant interaction occurs among the SWCNTs and Trp molecules adsorbed.However

negligible changes in the peak profiles and energy positions of nitrogen K-edge imply that neither of the two nitrogen atoms in Trp molecule is involved in the interface interaction.A change of the shape of the main absorption peak at the oxygen K-edge reveals that O atoms of the C=O or C-O or both are likely involved in the interface interaction.The fact that the peak at about 529 eV at the O K-edge become sharper and stronger demonstrates that the O atom in the C=O participates in the interface interaction

which was confirmed by O1s SRPES spectrum.