Abstract: The interaction between berberine and ct DNAwas investigated by using FT-Surface Enhancement Raman Scattering(SERS) spectroscopy. The FT-SERSspectra of berberine and its complex with DNAwere recorded in the Ag sol and pH7.20 Tris solution. Vibrational assignment of the SERSactive modes was done on the basis of normal coordinate analysis. Some Raman bands of berberine are dramatically increased in intensity on the silver colloid. Results suggest that berberine ring system around the nitrogen positively charged center should assume the perpendicular or at least tilted stances with respect to the surface of Ag sol nanoparticle through the electrostatic interaction. When ct DNAis added into the berberine solution, much stronger SERSsignal with a factor of 1.5 was obtained for the most of FT-SERSbands of the molecule due to DNAbinding; only a few bands approach to disappear in intensity. This result implies that there are two binding modes between berberine and double helix DNA. The shifts of some Raman band were also observed on the DNAbinding. SERSexperiments show that the isoquinolone moiety of berberine molecule may be accommodated in the minor groove of DNAhelix. Grooving binding is very likely to be the dominant mode in the interaction of berberine with double helix DNA.

Key words: Surface-enhanced Raman spectroscopy, Berberine, ct DNA