The orientation of protoberberine alkaloids and their binding activities to human serum albumin by surface-enhanced Raman scattering

Raman and surface-enhanced Raman scattering (SERS) technique are reliably used to compare relative intensity shifts and to investigate the adsorption geometry of protoberberine alkaloids on Ag nanoparticles. We report joint application of fluorescence and SERS spectroscopy to study the interaction between protoberberine alkaloids and human serum albumin (HSA). We propose SERS technique to improve the quenching interaction caused by protoberberine alkaloids which are used to be applied in recognition process of fluorescent drugs with large biomolecules. The fluorescence results show that the fluorescence intensity of HSA is significantly decreased in presence of protoberberine alkaloids. The SERS technique demonstrates obvious advantages over direct measurements in discriminating and identifying pharmaceutical molecules. By means of this method, we are able to detect important information concerning the orientation of protoberberine alkaloids when interacting with HSA. We also show that the nitrogen atom is free, but a benzene ring and two adjacent methoxy groups are involved in the spontaneously electrostatic inducement and subsequently binding with HSA.