Multifunctional NH2-Cu-MOF based ratiometric fluorescence assay for discriminating catechol from its isomers

Although fluorescent nanozymes exhibit great potential in sensing fields, few current nanozyme-based sensors are designed to discriminate catechol (CC) from its two isomers. Herein, fluorescent metal-organic framework (MOF)-based nanozyme is utilized for ratiometric and selective detection of CC without the interferences of hydroquinone (HQ) and resorcinol (RC). NH2-Cu-MOF plays multiple roles: (1) it exhibits excellent photoluminescence at 435 nm owing to the 2-amino-1,4-benzenedicarboxylic acid ligand; (2) Cu2+ imparts MOF oxidase activity to trigger the oxidation of o-phenylenediamine (OPD) into luminescent products (oxOPD) with emissive peak at 571 nm, which quenches the intrinsic fluorescence of NH2-Cu-MOF (435 nm) through inner filter effect (IFE); (3) Cu2+ can complex with CC specifically to produce complex containing o-semiquinone, which not only inhibits MOF's oxidase-like activity but also quenches the fluorescence of MOF. Therefore, the presence of CC induces the decrease of fluorescence at 571 nm followed by the slight recovery of fluorescence at 435 nm. Notably, HQ and RC have negligible influences on the fluorescence of NH2-Cu-MOFs/OPD system. Based on these facts, a ratiometric fluorescence platform for CC has been constructed. It exhibits high sensitivity towards CC with LOD of 0.1 mu M.