Interfacial Redox Recycling Nanocatalysts with Ultrahigh Peroxidase Activity for Colorimetric Sensing Applications

For the past few years, conventional peroxidase mimics of nanoscale materials have found limited applications because of their low catalytic activity. Hence, it is desirable to control and tune their physicochemical properties through precise engineering to achieve a superior catalytic efficiency. Herein, we demonstrate an efficient strategy for substantially improving the peroxidase-mimetic activity of nanomaterials, particularly those that exhibit mixed redox states. One of these synthesized redox-active nanostructures is plasmonic nanoceria (PNC), which consists of a cerium oxide core with several encapsulated plasmonic gold nanoparticles within its poly-(acrylic acid) polymer coating. PNC nanostructures exhibit enhanced catalytic activity with a K _cat value of 10⁶ s^-1, 10³-fold higher than that of natural enzymes. Importantly, the catalytic activity of PNC was present over a wide range of temperatures and pH. Density functional theory (DFT) calculations revealed that efficient electron transfer from gold (Au) to cerium (Ce) atoms in the PNC significantly boosts its catalytic activity. Using Escherichia coli O157:H7 as a target pathogen, it is demonstrated that when PNC is applied as a peroxidase mimic for an enzyme-linked immunosorbent assay (ELISA), lower limits of detection are achieved than in conventional assays employing natural enzymes.