Luminescent Metal–Organic‐Framework‐Based Label‐Free Assay of Polyphenol Oxidase with Fluorescent Scan

Metal–organic frameworks (MOFs) are emerging in recent years as a kind of versatile fluorescent sensing materials, but their application to enzyme assays has rarely been studied. Here, the first example of a MOF‐based label‐free enzyme assay system is reported. A luminescent MOF was synthesized and applied to the activity analysis of polyphenol oxidase (PPO). With its distinct responses to the phenolic substrate and o‐quinone product, this MOF could transduce the extent of PPO‐catalyzed oxidation to fluorescence signal and enable the real‐time monitoring of this reaction. Wide substrate adaptability and high sensitivity (detection limit=0.00012 U mL−1) were exhibited by this method, which meets the requirement of common bioanalysis. Interestingly, by the comparison with molecular capturing reagents, the heterogeneous nature of this MOF‐based assay effectively preventing the interaction with the enzyme was proven, thus ensuring the authenticity of results. MOF sensor: A luminescent metal‐organic framework (MOF) was synthesized and applied to the activity assay of polyphenol oxidase (PPO). With selective response to the o‐quinone product, this MOF sensor could reflect the kinetics of PPO‐catalyzed phenol oxidation through a fluorescence intensity change in real time. This label‐free heterogeneous method exhibits the advantages of high sensitivity, wide substrate adaptability, and minimal effects on the enzymatic reaction.