Accelerating the Phosphatase-like Activity of Uio-66-NH 2 by Catalytically Inactive Metal Ions and Its Application for Improved Fluorescence Detection of Cardiac Troponin I.

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).