Aspartic acid reprograms electronic and catalytic pathways of MIL-53(Fe) for neutral-pH cascade glucose sensing

Asp donates electrons to reprogram Fe O clusters of MIL-53(Fe). • This electronic switch redirects dominant ROS from •OH to •O 2 − . • The mechanism enables neutral-pH POD-like activity of MIL-53(Fe)@Asp. • The Asp-modified nanozyme integrates with GOX for cascade glucose sensing. MIL-53(Fe) exhibits peroxidase-like activity only under acidic conditions, limiting its biosensing applications. We overcome this by using aspartic acid (Asp) as a structure-directing agent to modify MIL-53(Fe) (MIL-53(Fe)@Asp) via hydrothermal synthesis followed by Asp coordination. Unlike conventional pH-reduction strategies, Asp modification does not alter bulk pH but induces intrinsic electronic restructuring of Fe O clusters, as confirmed by increased Fe 3+ /Fe 2+ ratio and introduction of N → Fe coordination (XPS). At pH 6.9, the TMB-based activity of MIL-53(Fe)@Asp is 27-fold higher than that of pristine MIL-53(Fe). Steady-state kinetics show favorable Km values (TMB 0.27 mM, H 2 O 2 1.38 mM) at neutral pH. Mechanistic studies (ROS identification, EPR, band structure, DFT) reveal that Asp exerts an electron-donating effect that reprograms the electron distribution of Fe O clusters, activating the otherwise inactive MIL-53(Fe) framework at neutral pH and diversifying the catalytic pathways to include a less pH-dependent •O 2 − route alongside the partially maintained •OH pathway. This pathway diversification enables efficient neutral-pH peroxidase-like catalysis, with •O 2 − as the dominant pathway. Leveraging this, we construct a cascade nanoplatform (MIL-53(Fe)@Asp@GOX) integrating glucose oxidase, which exhibits excellent cascade activity at neutral pH. The method is applied to glucose detection in blood and saliva, demonstrating good linearity, precision, selectivity, and recovery. The glucose concentrations determined by our sensor correlated well with those obtained using a commercial assay kit. Notably, the limit of detection for glucose in saliva reaches 2.08 μM, offering a promising route toward non-invasive glucose sensing. This work establishes a design principle for creating pH-adaptive catalytic microenvironments in Fe-MOFs through electronic restructuring and pathway diversification, overcoming a long-standing limitation of MIL-53(Fe) for biomedical applications. Download: Download high-res image (111KB) Download: Download full-size image