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

As alternatives to natural peroxidase, peroxidase mimics made of inorganic nanomaterials have been extensively developed for a variety of biosensing applications in recent years. In this work, we report an innovative concept to design and synthesize peroxidase mimics for sensitive biosensing–engineering thin metallic nanowires with narrow diameters (<5 nm), high aspect ratios, and branched structures. The nanowire has a significantly larger total surface area than conventional three-dimensional peroxidase mimics, ensuring a high catalytic efficiency. Moreover, the thin nanowires with good mechanical flexibilities induce minimal steric effects during biosensing. Using iridium (Ir) nanowires as a model example, we demonstrate that the nanowires could achieve an ultralow detection limit of 0.92 pg/mL in immunoassay of carcinoembryonic antigen (a biomarker for recurrence of colorectal cancer), which is 42- and 370-fold lower than the detection limits of conventional Ir nanoparticle- and enzyme-based immunoassays, respectively. The concept of crafting thin nanowires as peroxidase mimics was successfully extended from Ir to platinum- (Pt) and Ir-Pt-alloyed nanowires.