Electrochemical immunosensors with protease as the signal label for the generation of peptide-Cu(II) complexes as the electrocatalysts toward water oxidation

•Protease can be used as the signal label of electrochemical biosensors.•Protease catalyzed the generation of a Cu(II)-binding peptide.•The peptide-Cu(II) complex exhibits an electrocatalytic ability for water oxidation.•The signal was amplified by enzyme label and redox cycling of peptide-Cu(II) and H2O.•The detection limit of this method for prostate-specific antigen is down to 10 pg/mL.