A colorimetric method for determination of the prostate specific antigen based on enzyme-free cascaded signal amplification via  peptide-copper(II) nanoparticles.

Biotinylated peptide-Cu2+ nanoparticles (Cu-P NPs) were synthesized via "one-pot" self-assembly. The peptide P conststs of a hydrophobic dipeptide (FF), a tripeptide (KGH), and a biotin moiety attached to the terminal amino group of the Lys residue. The Cu-P NPs contain abundant catalytically active Cu2+ ions which are liberated by acid-induced dissolution. The released Cu2+ ions catalyze the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 because of their intrinsic peroxidase activity, and this results in the formation of a blue-green coloration. Based on the streptavidin-biotin interaction, the Cu-P NPs were employed to establish an enzyme-free colorimetric method for determination of prostate-specific antigen (PSA) as a model biomarker. Under optimal conditions, the linear response range is 0.001-1 ng mL-1, with a limit of detection as low as 1 pg mL-1. Graphical abstract Schematic illustration of a colorimetric immunoassay for the prostate specific antigen (PSA) with biotinylated peptide-Cu2+ nanoparticle (Cu-P NP) as the signal label based on the streptavidin (SA)-biotin interaction. The signal was produced by Cu2+-catalyzed oxidization of 3,3',5,5'-tetramethylbenzidine (TMB). P: KGHFF.