The interaction of dsDNA and ssDNA with two osmium complexes has been studied by surface electrochemical methods based on DNA modified electrode to find that both osmium complexes could bind DNA with electrostatic interaction even at high ionic strength. And some thermodynamic and kinetics constants, such as binding constant K_3＋ or K_2＋, ratio of binding constants K_3＋/K_2＋, limiting ratio at zero ionic strength (I_i＝0), free energy ΔG_b, dissociation rate constant k and binding site size s (base pair) have been obtained.

Key words: DNA, osmium complex, interaction, surface electrochemistry