Copper-doped mesoporous silica nanoparticles for constructing a single-particle enzyme-nanozyme cascade sensing system.

Copper-doped mesoporous silica nanoparticles (Cu-MSNs) were developed as multifunctional carriers to construct a single-particle enzyme-nanozyme cascade system for colorimetric glucose detection. The mesoporous framework provided abundant sites for glucose oxidase (GOx) immobilization and substrate diffusion, while the incorporated Cu⁺/Cu2+ species acted as catalytic active sites that endowed Cu-MSNs with peroxidase-like activity, enabling hydrogen peroxide (H2O2) activation and 3,3',5,5'-tetramethylbenzidine (TMB) oxidation. GOx was immobilized onto amino-functionalized Cu-MSNs through electrostatic interactions to form GOx@Cu-MSNs. In this system, GOx catalyzed glucose oxidation to generate H2O2, which was then activated by Cu-MSNs to produce hydroxyl radicals and oxidize TMB into a blue product. The spatial integration of GOx and Cu catalytic sites within one particle facilitated intermediate utilization and enhanced cascade signal amplification compared to a physical mixture of free GOx and Cu-MSNs. After integration with a paper-based analytical device (PAD), the GOx@Cu-MSNs-modified PAD enabled smartphone-assisted glucose detection with a linear range of 20-400 µM and a detection limit of 13.6 µM. The PAD showed good selectivity, retained 95% of its initial response after 21 days of storage, and maintained the response in artificial and real sweat samples. This work provides a portable visual strategy with initial feasibility for sweat glucose analysis and demonstrates the potential of Cu-MSNs for building expandable enzyme-nanozyme cascade sensing platforms.