The inclusion of β-cyclodextrin (CD) for thionine (TH) and the interaction of DNA with CD-TH inclusion complex were investigated by fluorescence and visible absorption spectrometry. TH with β-CD formed a 1:1 inclusion complex with the stability constant of 527 L·mol-1 (visible spectrometry)/444 L·mol-1 (fluorescence) in the pH 7.2 PBS buffer solutions. The addition of DNA makes the absorbance of the inclusion complex decrease and the absorption spectrum shift toward long wavelengths. The fluorescence experiments indicated that the presence ...