Enhanced Oxidase-Like Activity of Cu-MOF Nanozyme by 1,4-Dioxane To Improve Distinguishing Isomers and Sensing Performance

Nanozymes have drawn great attention in the development of environmental pollutant sensors. However, their inferior catalytic activities limit their further application. Herein, we find that the presence of 1,4-dioxane boosts the oxidase-like activity of the copper-based metal-organic framework (Cu-MOF) remarkably through improving its dispersity. The exposed more active sites promote the decomposition efficiency of O₂ to produce more reactive oxygen species (ROS), which are utilized to oxidize aromatic amines. Environmental pollutant phenylenediamine isomers display different responses when being oxidized by Cu-MOF, and the addition of 1,4-dioxane amplifies these differences, which provides a highly sensitive method to identify o-phenylenediamine (OPD), m-phenylenediamine (MPD), and p-phenylenediamine (PPD). OPD is oxidized by Cu-MOF to produce yellow fluorescent product oxOPD (λ_em = 565 nm), which, in turn, quenches the blue fluorescence of Cu-MOF (λ_em = 435 nm), forming a dual-emissive probe. Sn²⁺ inhibits the catalytic oxidation ability of Cu-MOF toward OPD, leading to the fluorescence decrease at 565 nm and the increase of emission at 435 nm, respectively. Furthermore, noticeable color changes from yellow to blue are observed. With the assistance of a smartphone, quantitative visual detection of Sn²⁺ is obtained with a limit of detection (LOD) of 2.0 μM. Besides demonstrating an amplified method for the detection of phenylenediamine isomers and Sn²⁺, this work provides new insights for improving the catalytic activity of nanozymes to boost the development of sensors.