Accelerating the Phosphatase-like Activity of Uio-66-NH₂ by Catalytically Inactive Metal Ions and Its Application for Improved Fluorescence Detection of Cardiac Troponin I

Abstract

Compared with natural enzymes, nanozymes usually exhibit much lower catalytic activities, which limit the sensitivities of nanozyme-based immunoassays. Herein, several metal ions without enzyme-like activities were engineered onto Uio-66-NH 2 nanozyme through postsynthetic modification. The obtained M n+ @Uio-66-NH 2 (M n+ = Zn 2+ , Cd 2+ , Co 2+ , Ca 2+ and Ni 2+ ) exhibited improved phosphatase-like catalytic activities. In particular, a 12-fold increase in the catalytic efficiency (k cat /K m ) of Uio-66-NH 2 was observed after the modification with Zn 2+ . Mechanism investigations indicate that both the amino groups and oxygen-containing functional groups in Uio-66-NH 2 are the binding sites of Zn 2+ , and the modified Zn 2+ ions on Uio-66-NH 2 serve as the additional catalytic sites for improving the catalytic performance. Furthermore, the highly active Zn 2+ @Uio-66-NH 2 was used as a nanozyme label to develop a fluorescence immunoassay method for the detection of cardiac troponin I (cTnI). Compared with pristine Uio-66-NH 2 , Zn 2+ @Uio-66-NH 2 can widen the linear range by 1 order of magnitude (from 10 pg/mL−1 μg/mL to 1 pg/mL−1 μg/mL) and also lower the detection limit by 5 times (from 4.7 pg/mL to 0.9 pg/mL).