with time corresponds to the latter process. All above conjectures, obtained from spec- troscopic measurements, can be further confirmed by studying interaction of Ag-lysozyme complexes with other ligands that are currently underway, for which the interaction sites of lysozyme are already established. As mentioned earlier that there are few reports in which SERS spectra of lysozyme molecules on Ag colloidal surface have been discussed. Prior knowledge available on the interaction of the Ag-nanoparticles with lysozyme indicates the α -helical and random coil components [9]. Our experimental approach identifies the particular Trp residue involved in the interaction. Besides this, the effect of the interaction on the intensities of SERS bands of Phe and disulfide bonds confirm the specific site of the protein involved in the complexa- tion. Conformational changes in the protein molecule on interaction with Ag nanoparticles indicate partial unfolding of the α -helix constituted of residues 25-35 of which Phe-34 is a member. Interestingly, it is to be noted that the parts of the protein molecule with β -sheet comprising of Trp-62 and Trp-63, known to have higher bio-activity, remain unaffected by metal-protein complexation. AR and SDG thank DRDO, India for financial assistance Acknowledgements 10