The electrochemistry of deoxyribonucleic acid-cetyltrimethylammonium complex (DNA-CTMA) film is studied by cyclic voltammetry. DNA-CTMA film is electroactive, but the electrochemical redox processes are not reversible. The experimental results indicate that O-2 can oxidize both guanine in CH2Cl2 and deprotonated guanine in aqueous NaOH electrolyte. O-2 is responsible for the negative shift of the oxidation potential of guanine. The exclusion of O-2 can protect guanine from chemical oxidation and result in reliable evaluation of HOMO (highest occupied molecular orbital) level based on the onset oxidation potential of DNA-CTMA. The HOMO level of DNA-CTMA is derived to be 5.68 eV from the cyclic voltammetry. (C) 2013 Elsevier B.V. All rights reserved.