SERS study of different configurations of pharmaceutical and natural product molecules ginsenoside Rg3 under the interaction with human serum albumin on simple self-assembled substrate.

Surface-enhanced Raman scattering (SERS) and fluorescence spectroscopy were employed to probe the interaction of the pharmaceutical and natural product molecules, 20(R) and 20(S)-ginsenoside Rg3, with human serum albumin (HSA). Normal Raman spectra of 20(R) and 20(S)-ginsenoside Rg3 were obtained from solid powder on glass slide. Based on the splitting peaks near 1440 cm(-1), the stacking modes of 20(R) and 20(S)-ginsenoside Rg3 were quite different. SERS spectra of both R and S configurations were obtained from a colloidal silver surface on a self-assembled SERS substrate, the most enhanced modes of 20(R) and 20(S)-ginsenoside Rg3 were those with certain motions perpendicular to the metal surface. The SERS spectra were used to predict a common orientation geometry for the alkyl chain portion of the drugs on the colloidal surface with a minor difference in the carbocyclic rings. Nevertheless, once combined with HSA, the flexible portion of alkyl chains assumes a collectively similar conformation on the Ag surface with the glucose rings perpendicularly plugging into the hydrophobic site of HSA.