Bifunctional Block Polymer-Engineered Platinum Nanozymes for Ultrasensitive Immunoassay

This study presents a sensitive and facile strategy for dual modulation of the catalytic activity of nanozymes through surface ligand engineering and size effects. Four different capped polymers, including poly(vinyl acrylate) (PVA), polyvinylpyrrolidone (PVP), polystyrenesulfonate (PSS), and poly(acrylic acid) (PAA), were used to synthesize Pt nanoparticles (Pt NPs) to reduce aggregation and improve their catalytic activity. Notably, PVA-modified Pt NPs exhibited up to 3.6 μM s^-1 of peroxide mimetic enzyme activity, which was 18 times as much as that of Pt NPs modified with the commonly used surfactant PVP (0.038 μM s^-1). Mechanistic studies further exhibited that the surface polymer could accept the negative charge of Pt, thus reducing the affinity between Pt and the intermediate species. Under optimal conditions, the nanozymatic immunoassay constructed based on Pt@PVA exhibited an ultralow detection limit (4.06 pg mL^-1) and a good linear range (0.01-10 ng mL^-1) for the detection of carcinoembryonic antigen (CEA). This study provides a feasible route for designing nanozymes with high specific activity through surface engineering, which further expands the scope of nanozymes for research and application.