Metal Site and Size-Controlled BTC-Based MOF as Cysteine Oxidase Mimic for Self-Cascade Detection of Cysteine and Hg 2 .

Nanozyme-mediated strategy for sensing has been widely applied nowadays, in which the construction of a nanozyme cascade platform is an effective and challenging method to simulate the complexity and multifunctionality of natural systems. Herein, a simple and convenient self-cascade sensing platform was developed for the fluorescent detection of cysteine and Hg 2+ by a BTC-based MOF through screening the metal sites and crystal sizes. By the introduction of polyvinylpyrrolidone, the as-prepared Cu-BTC possessed a metal center of Cu 2+ and smaller size, which exhibited both cysteine oxidase- and peroxidase-like activities. The dual enzymic characters of Cu-BTC made a self-cascade reaction occur during which cysteine was first oxidized to cystine and generated H 2 O 2 in the presence of O 2 , then H 2 O 2 was decomposed into ·OH, and finally the ·OH triggered the turn-on fluorescence of Cu-BTC. Based on the self-cascade reactions and high affinity of Hg 2+ and -SH within cysteine, a fluorescent method was developed to detect cysteine and Hg 2+ with a range of 0-160/0-15 μM and a limit of detection of 0.04/0.09 μM, respectively. This work reveals the important role of the Cu 2+ center for mimicking cysteine oxidase and gives a feasible strategy for constructing simple self-cascade reactions.