The fabrication and electrochemical interrogation of very high density single-antibody nanoarrays is reported. Gold nanodots, 15 nm in diameter, arranged in large (cm²) square arrays with a pitch of 200 nm, are used as carriers for primary antibodies (immunoglobulin G (IgG)), further recognized by secondary redox-labeled detection antibodies. Ensemble scale interrogation of the antibody array by cyclic voltammetry, and nanoscale interrogation of individual nanodots by mediator tethered atomic force-scanning electrochemical microscopy (Mt/AFM-SECM), enable the occupancy of nanodots by single antibody molecules to be demonstrated. Experiments involving the competitive adsorption of antibodies of different species onto the nanodots evidence the possibility of using single-antibody nanoarrays for digital electrochemical immunoassays.