Exploring the role of ligand-BSA in the response of BSA-protected gold-nanoclusters to silver (I) Ions by FT-IR and circular dichroism spectra

Previously, we have explored the mechanism of the response of BSA-protected small gold nanoclusters (Au16NCs@BSA) to silver (I) ions (Ag+) by using XPS, but the role of the ligand BSA in this response was not clear. Therefore, we used FT-IR and circular dichroism (CD) spectra to monitor the changes of the secondary structure of ligand BSA. After adding Ag+ to the AuNCs@BSA, compare with the native BSA, the ligand-BSA showed little differences in the position of main peaks but more differences in the profile of this peak in FT-IR spectra. While in CD spectra it is not only peak shape changed but also peak position. All the results showed silver ions can bind to ligand BSA, and induced their secondary structure changes. But the changes of ligand BSA are not enough to influence the fluorescence emission of AuNCs@BSA, especially for the emission of AuNCs. And BSA-protected different size gold nanoclusters have the similar changes in spatial structure of ligand BSA, but only the Au16NCs@BSA could response to Ag+, which indicated that the ligand BSA was not the key role for the special fluorescent response.