The quadruplex-targeting anticancer drug BRACO-19 adsorption and redox behaviour were investigated by atomic force microscopy (AFM) on a highly oriented pyrolytic graphite surface and by cyclic, differential pulse and square-wave voltammetry at a glassy carbon electrode. The AFM and voltammetric results demonstrated that the BRACO-19 orientation and strong adsorption, with the acridine aromatic core parallel or perpendicular to the carbon electrode surface depending on solution pH, directly influences the peak potentials and redox behaviour. BRACO-19 oxidation was a complex, pH-dependent, four-step electrode process. The first oxidation step was reversible, the second, third and fourth oxidation steps irreversible, and an electroactive irreversibly oxidized BRACO-19 oxidation product was formed. BRACO-19 reduction occurred in two irreversible, pH-independent steps. The proposed redox mechanisms are related to the pyrrolidine and acridine moieties. (C) 2015 Elsevier Ltd. All rights reserved.