[Ru(bpy)2dppz]2+ electrochemiluminescence (ECL) was studied, and it was used to investigate DNA interaction and develop a label-free ATP aptasensor for the first time. ECL of [Ru(bpy)2dppz]2+ is negligible in aqueous solution, and increases approximately 1000 times when [Ru(bpy)2dppz]2+ intercalates into the nucleic acid structure. The ECL switch behavior of [Ru(bpy)2dppz]2+ is ascribed to the intercalation that shields the phenazine nitrogens from the solvent and results in a luminescent excited state. The ECL switch by DNA was applied to investigate the interaction of [Ru(bpy)2dppz]2+ with herring sperm DNA. The calculated equilibrium constant (K) is 1.35 x 10(6) M(-1), and the calculated binding-site size (s) is 0.88 base pair, which is consistent with the reported values. Moreover, ATP can dramatically affect ECL of the [Ru(bpy)2dppz]2+/ATP aptamer complex. As a result, a label-free, sensitive, and selective [Ru(bpy)2dppz]2+ ECL method for ATP detection was developed. The detection limit is 100 nM for ATP (with a signal-to-noise ratio, S/N, of 3) with a linear range of 0-1 microM. The result demonstrates that [Ru(bpy)2dppz]2+ ECL holds great promise in aptasensors.