We report quantitative results on interactions between a tumor suppressor protein, p53, also known as a prognostic cancer marker, and its antibody. The p53 antibody molecules immobilized on an (R)-lipo-diaza-18-crown-6 self-assembled monolayer (SAM)-modified gold disk electrode were shown to effectively capture the p53 protein by Western blot, quartz crystal microbalance, and electrochemical impedance experiments. The p53 protein thus captured modulated the ability of the electrode for charge transfer to and from a redox probe in the solution in a p53 concentration range of approximately 0.1-30 microg/mL. The same interaction was also observed in the human embryonic kidney cell lysate, demonstrating that the SAM-modified electrode can serve as a selective platform for electrochemically monitoring the cellular p53 concentration.