Heterovalent Co Doping Boosts the Phosphatase-like Activity of UiO-66-NH ₂ for Ultrasensitive Fluorescence Immunoassay of CEA

To overcome the limitation of low catalytic activity in nanozyme labels for immunoassay, this study proposed a heterovalent Co-doping strategy to construct the bimetallic Zr/Co-UiO-66-NH₂ nanozyme. Compared to the undoped UiO-66-NH₂, the resulting nanozyme exhibited a 14-fold enhancement in phosphatase-like catalytic efficiency (<i>k</i>_cat/<i>K</i>_m). Mechanistic investigations revealed that the activity enhancement was not only dependent on the high specific surface area and increased defects introduced by heterovalent Co doping, but also was attributed to the electronic synergy between Zr and Co. Furthermore, a fluorescent immunoassay method utilizing highly efficient Zr/Co-UiO-66-NH₂ as the nanozyme label was developed for the ultrasensitive detection of carcinoembryonic antigen (CEA). This method achieved a broad linear detection range spanning 6 orders of magnitude (1 × 10^-12 g/mL to 1 × 10^-6 g/mL) and a detection limit as low as 0.74 × 10^-12 g/mL. The high recovery rates (95.89%-99.31%) in serum samples demonstrate great potential for the detection of CEA in complex biological matrices.