Enzyme-mimicking activity of iron oxide based nanostructures have provided a significant advantage in developing advanced molecular sensors for biomedical and environmental applications. Herein, we introduce the horseradish peroxidase (HRP)-like activity of gold loaded nanoporous ferric oxide nanocubes (Au-NPFe2O3NC) for the development of a molecular sensor with enhanced electrocatalytic and colorimetric (naked-eye) detection of autoantibodies. The results showed that Au-NPFe2O3NC exhibits enhanced peroxidase-like activity towards the catalytic oxidation of 3,3ˊ,5,5ˊ-tertamethylbenzidine (TMB) in the presence of H2O2 at room temperature (25°C) and follows the typical Michaelis–Menten kinetics. The autoantibody sensor based on this intrinsic property of Au-NPFe2O3NC resulted excellent detection sensitivity (LOD = 0.08 U/mL) and reproducibility (% RSD = < 5% for n = 3) for analysing p53-specific autoantibodies using electrochemical and colorimetric (naked-eye) readouts. The clinical applicability of the sensor has been tested in detecting p53-specific autoantibody in plasma obtained from patients with epithelial ovarian cancer high-grade serous subtype (EOCHGS, number of samples = 2) and controls (benign, number of samples = 2). As Au-NPFe2O3NC possess high peroxidase-like activity for the oxidation of TMB in the presence of H2O2 (TMB is a common chromogenic substrate for HRP in ELISAs), we envisage that our assay could find a wide range of application in developing ELISA based sensing approaches in the field of medicine (i.e. detection of other biomarkers same as p53 autoantibody), biotechnology and environmental sciences.