Life-threatening allergies to peanuts and tree nuts can be revealed by detecting antibodies (IgEs) to their allergens in patient serum. Herein, we compare several immunosensor-like methodologies for sensitive detection of antibodies to a peptide sequence from the major peanut allergen, Arachis hypogaea 2 (Ara h2). The sensors feature a synthetic peptide layer of the major IgE-binding epitope from Ara h2 attached to a dense gold nanoparticle (AuNP) film on a pyrolytic graphite (PG) electrode. The AuNP-peptide sensor was used to determine model chicken antipeanut antibodies (IgY) in serum. Faradaic and nonfaradaic impedance strategies were compared to amperometric detection. Measurements employed goat antichicken secondary antibodies (Ab(2)) labeled with horseradish peroxidase (HRP) to bind to IgY on the sensor and provide amplified signals. The best impedimetric sensor configuration featured HPR-catalyzed precipitation of the enzyme product onto the sensor measured by nonfaradaic impedance. This sensor configuration had the best detection limit (DL) of 5 pg mL(-1) and the best linear range of over 5 orders of magnitude (from 5 pg mL(-1) to 1 microg mL(-1)) for IgY antibody in undiluted calf serum. This DL was 100-fold lower than label-free impedimetric immunosensors (0.5 ng mL(-1)) and 60-fold lower than when using HRP-Ab(2) in amperometric immunosensors (0.3 ng mL(-1)).