Glutamate Oxidase-Integrated Biomimetic Metal–Organic Framework Hybrids as Cascade Nanozymes for Ultrasensitive Glutamate Detection

The hybrid coupling of biocatalysts and chemical catalysts plays a vital role in the fields of catalysis, sensing, and medical treatment due to the integrated advantages in the high activity of natural enzymes and the excellent stability of nanozymes. Herein, a new nanozyme/natural enzyme hybrid biosensor was established for ultrasensitive glutamate detection. The MIL-88B(Fe)-NH2 material with remarkable peroxidase mimic activity and stability was used as a nanozyme and carrier for immobilizing glutamate oxidase (GLOX) through Schiff base reaction to construct a chem-enzyme cascade detector (MIL-88B(Fe)-NH2@GLOX). The resultant MIL-88B(Fe)-NH2@GLOX exhibited a wide linear range (1-100 μM), with a low detection limit of 2.5 μM for glutamate detection. Furthermore, the MIL-88B(Fe)-NH2@GLOX displayed excellent reusability and storage stability. After repeated seven cycles, MIL-88B(Fe)-NH2-GLOX (GLOX was adsorbed on MIL-88B(Fe)-NH2) lost most of its activity, whereas MIL-88B(Fe)-NH2@GLOX still retained 69% of its initial activity. Meanwhile, MIL-88B(Fe)-NH2@GLOX maintained 60% of its initial activity after storage for 90 days, while free GLOX only retained 30% of its initial activity. This strategy of integrating MOF mimics and natural enzymes for cascade catalysis makes it possible to design an efficient and stable chemo-enzyme composite catalysts, which are promising for applications in biosensing and biomimetic catalysis.