Electrochemical biosensors have substantial advantages for portable and implantable applications, including their greater simplicitiy and lower noise levels. We report an electrochemical impedance immunosensor for peanut protein Ara h 1 constructed by surface immobilization of a polyclonal antibody to this protein on both Au and degenerate Si substrates. Immobilization onto both substrates occurs through amide bond formation using standard EDC/NHSS synthesis methods. Degenerate Si offers the advantage of increased sensor stability due to direct Si-C bond formation, as well as reversble electrochemistry. Accidental ingestion of peanut proteins is a severe public health hazard, with over 100 fatalities in the USA alone each year. Impedance sensing of peanut protein Ara h 1 at an Au electrode is demonstrated with a detection limit of less than 5.0 μg/ml.