The aqueous electrochemistry of Dy@C-82 films and membrane films of didodecyldimethylammonium bromide (DDAB) encapsulated with DY@C-82 has been studied systematically. The redox responses of the Dy@C-82 films depend strongly on the supporting electrolytes. In the aqueous solution of tetrabutylammonium bromide, we obtained four cathodic waves at 0.040, -0.40, -1.04, and -1.35 V, and one oxidation wave at +0.31 V. For the membrane films of Dy@C-82-DDAB film, however, the well-defined redox responses in water are relatively independent of the supporting electrolytes because of the encapsulation and fine dispersion of Dy@C-82 in the DDAB membrane. Reversible reduction and oxidation waves were obtained even in the pH 7.0 buffer solution containing KCl, which is associated with the charge balance of the DDAB ions with the ions of Dy@C-82. It was found that DY@C-82 in the DDAB membrane promotes the encapsulation of hemoglobin (Hb) and Hb can catalyze the reduction of DY@C-82. Significantly enhanced electrocatalytic reduction of O-2 by Hb in the presence of Dy@C-82 has also been demonstrated. Here Dy@C-82 acts an electron-transfer mediator, which points to the potential application of metallofullerenes in biochemical sensing. (C) 2004 Elsevier B.V. All rights reserved.