Ir- and Pt-Based Nanowires as Peroxidase Mimics for Detection of Carcinoembryonic Antigen

As alternatives to natural peroxidase, peroxidase mimicsmade ofinorganic nanomaterials have been extensively developed for a varietyof biosensing applications in recent years. In this work, we reportan innovative concept to design and synthesize peroxidase mimics forsensitive biosensing-engineering thin metallic nanowires withnarrow diameters (<5 nm), high aspect ratios, and branched structures.The nanowire has a significantly larger total surface area than conventionalthree-dimensional peroxidase mimics, ensuring a high catalytic efficiency.Moreover, the thin nanowires with good mechanical flexibilities induceminimal steric effects during biosensing. Using iridium (Ir) nanowiresas a model example, we demonstrate that the nanowires could achievean ultralow detection limit of 0.92 pg/mL in immunoassay of carcinoembryonicantigen (a biomarker for recurrence of colorectal cancer), which is42- and 370-fold lower than the detection limits of conventional Irnanoparticle- and enzyme-based immunoassays, respectively. The conceptof crafting thin nanowires as peroxidase mimics was successfully extendedfrom Ir to platinum- (Pt) and Ir-Pt-alloyed nanowires.