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

Abstract This work reported that protease can be used as the signal label to amplify the signal of electrochemical immunosensors. Carbon nanotube (CNT) was used as the carrier of recognition antibody and signal label. The nanolabel was captured by sensor electrode via a sandwich-type immunoreaction. Protease on the surface of nanolabel can catalyze the hydrolysis of peptide substrate to liberate an amino terminal Cu(II)- and Ni(II)-binding (ATCUN) peptide. The released ATCUN peptide can bind with Cu(II) to generate an electrocatalyst which exhibits high electrocatalytic ability for water oxidation. Thus, the signal was amplified again by the redox cycling between ATCUN-Cu(II) and H 2 O. The immunosensor exhibits low background current because of the poor redox activity of peptide substrate and the high oxidation overpotential of H 2 O molecule. Based on the signal amplification of protease and redox cycling, the target concentration as low as 10 pg/mL can be readily measured with prostate-specific antigen (PSA) as the model analyte. The proposed immunosensor was applied to determine PSA in human serum samples with satisfactory results.