Emission of thioflavin T and its control in the presence of DNA

The interaction of thioflavin T, 3,6-dimethyl-2-(4-dimethylaminophenyl)-benzothiazolium cation (TFT) with DNA is studied using absorption and emission spectral methods. The observed hypochromism in the absorption spectra suggests that the TFT binds with DNA. The emission spectral changes show two different emission bands at 450 and 485 nm for TFT in the presence of DNA. The emission intensity observed at 450 nm decreases upon increasing the concentration of DNA. This further confirms the binding of TFT with DNA. The new emission band observed at 485 nm for TFT increases with increasing the concentration of DNA. It is proposed that the binding of TFT with DNA facilitates the formation of emittive TFT dimer. An isoemissive point was observed at 464 nm when the DNA concentration was higher than 1.35 x 10(-5) mol dm(-3). This observation indicates the conversion of monomer TFT to emittive TFT dimer. Both the absorption and emission spectral studies show that two types of bindings such as groove binding and electrostatic interaction are present in the TFT-DNA system. The addition of NaCl to TFT-DNA showed the removal of the electrostatic binding between TFT and DNA. The intensity of 485 nm emission band is decreased upon the addition of NaCl to TFT-DNA system. The interaction of Na+ ions with the phosphate groups of the DNA blocked the electrostatic interaction of TFT cations with DNA. The emission band at 485 nm shows only one type of interaction viz. the electrostatic interaction. The three-dimensional emission spectral studies shows only one contour due to monomer TFT emission in the absence of DNA. However, in the presence of DNA, TFT shows two contours due to monomer TFT and emittive TFT dimer. (C) 2004 Elsevier B.V. All rights reserved.