Perovskite oxides offer new opportunities in wastewater treatment via catalytic oxidation. Herein, we report a new application of perovskite oxides for biological detection via catalytic decolourisation and calorimetric determination. The presence of trace biomolecules in an aqueous system would interfere the decolourisation process of dyes, where the decolourisation rate is quantitatively correlated to the biomolecular concentration. In this work, trace L-cysteine (Cys) detection was demonstrated on the basis of a Ag-Ba0.5Sr0.5Co0.75Fe0.2O3-delta (Ag-BSCF)/peroxymonosulfate/textile dye system. Thiol-containing cysteine can bind to Ag, Co and Fe atoms, therefore shielding the catalytic performance of the perovskite in degradation of dye solutions. Such a cost-effective biosensor system presents an excellent linear response in Cys concentration ranging from nM to mu M. (C) 2019 Elsevier Inc. All rights reserved.