Controllable Fabrication of Hg–Pd–PdO Heterostructures as Efficient Peroxidase Mimics for Carcinoembryonic Antigen Detection

The growth of oxides on the surface of noble metals and the introduction of alloys are effective methods to enhance the catalytic activity of noble metals. However, the fabrication of noble metal oxides always involves harsh experimental conditions and the oxidation degree could not be controlled. Herein, a simple, fast, and controlled Pd oxidation method by mixing Hg 2+ and Pd nanosheets (PdNSs) under mild conditions to form Pd x Hg y (PdO) z (PHOs) was reported, which consists of the Pd–Hg alloy and PdO. The density functional theory (DFT) calculation and experiment results proved that the Hg atom incorporation promotes the nearby Pd–Pd bond breaking, initiating a cascade of PdO generation. More precisely, 1 Hg atom incorporation induced ∼8 Pd atom oxidation, ensuring that the oxidation degree of Pd could be easily controlled by adjusting the ratio of Hg 2+ and PdNS. As a peroxidase-mimicking nanozyme, the PHO affinity for its substrate could be 21.7- and 123.6-fold greater than that of the PdNS and the natural peroxidase (HRP), respectively. For the colorimetric immunoassay of carcinoembryonic antigen (CEA) detection, PHO has an ultralow detection limit of 1.33 pg mL –1, which is ∼8.6 and ∼282 times lower than that of the PdNS and the natural HRP, respectively.