The cancer treatment based on monoclonal antibodies has become one of the most successful therapeutic strategies. Among the monoclonal antibodies, nivolumab (NIVO) stands out as being a relatively new anticancer drug. The NIVO‐dsDNA interaction was evaluated, in incubated solutions, by differential pulse voltammetry, UV‐Visible spectrophotometry and gel electrophoresis, and in situ with dsDNA‐, poly[G]‐ or poly[A]‐electrochemical biosensors, by differential pulse voltammetry, electrochemical impedance spectroscopy, and quartz crystal microbalance. The interfacial behaviour of the dsDNA‐electrochemical biosensor was also investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The NIVO‐dsDNA interaction mechanism caused, for shorter times, the binding of the NIVO to DNA, resulting in a NIVO‐dsDNA complex, and for longer times, the relaxation/unwinding of this complex structure. The monoclonal antibody NIVO did not promote oxidative damage to DNA.