Interaction Between Methylene Blue and ctDNA by Time-resolved Spectroscopy

The singlet oxygen( O-1(2) ) kinetics process of methylene blue( MB ) -ctDNA mixed solutions in D2O was studied by time-resolved spectroscopy, which helped to further investigate the interaction of MB and DNA. The results showed that O-1(2) phosphorescence kinetic curves of MB-ctDNA solutions at low concentrations of ctDNA and high concentrations of ctDNA had obvious differences, these differences were ascribed to the change of MB and DNA binding mode and the interaction mechanism. At low ctDNA concentration, ionic conjugate formed between MB molecules and ctDNA, significant hypochromic effect was observed in MB absorption band, and O-1(2) production dropped sharply with ctDNA. concentration increasing, but there were no obvious interaction between ctDNA and O-1(2); at high ctDNA concentration, interaction mode between MB molecules and ctDNA changed to intercalative binding, energy transfer between the excited state MB molecules and ctDNA as well as the effect of medium viscosity changed property of the O-1(2) dynamics, which greatly decreased the production of O-1(2), but ctDNA did not quench the O-1(2) apparently. These results indicated that type II photosensitization of O-1(2) damaging DNA was not the major mechanism of photodynamic therapy( PDT ) action in MB-DNA solutions.