Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)This work presents an in situ route to electrochemically prepare an oxidized carbon surface from glassy carbon electrodes (GCEs), which generates a material with a similar electrochemical response as graphene oxide. The proposed in situ route is fast, simple, environmentally friendly and consists in applying a potential of +1.8V vs. SCE to a GCE. The oxidized electrode surface (GCE(OS)) and its subsequent electrochemical reduction (GCE(ERS)) can be accomplished easily and efficiently by electrochemical techniques. GCE(OS) and GCE(ERS) were characterized by electrochemical, spectroscopic and microscopy techniques, revealing the insitu origin of the material and confirming its chemical similarity to the graphene oxide prepared by the Hummers and Tour methods. The presence of a 2D atomically thick material was not observed, which strongly indicates that the electrochemical response of graphene oxide resides only in the oxygenated functional groups. The remaining oxygenated groups in GCE(ERS) show a drastic cathodic shift of potential (542mV) for nicotinamide adenine dinucleotide (NADH) electrooxidation.25 761767Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)National Institute of Science and Technology in Bioanalytics (INCTBio)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)