Abstract: Spectral properties of two thiazole orange derivatives(TO-1 and TO-2) binding with nucleic acids and proteins are studied.It is found that side chains which linked to the nitrogen of the quinoline ring of thiazole orange have an important effect on fluorescent properties of dyes binding with macrobiomolecules.When carboxyl is introduced into TO-2,the fluorescent performance of TO-2 with nucleic acid declines.However,TO-2 has a good fluorescent performance when binding with the protein.From the study,it shows that introducing a proper hydrophilic side chain into the dye will extend the application of thiazole orange derivatives to the field of protein labeling.The paper also studies the fluorescent properties of TO-2 with the protein when changing the concentrations of the protein and changing the pH value of buffer solutions.

Key words: thiazole orange, nucleic acid, protein, fluorescent spectra