FePtCoNiCu High-Entropy Nanozymes Embedded in a Hydrogel Matrix as a Portable, Rapid, and Visual On-Site Biosensing Platform

High-entropy nanozymes (HEzymes) have garnered significant interest due to their multifunctional active sites and synergistic metal interactions, yet their applications in advanced biosensing, especially for portable on-site detection, remain underexplored. Herein, by integrating FePtCoNiCu HEzymes into a hydrogel matrix, we established aportable, cost-effective, and user-friendly system for on-site visual detection without complex instrumentation. Our HEzymes were facilely fabricated via a low-temperature oil-phase process and exhibit robust peroxidase-like (POD-like) activity through efficient conversion of H 2 O 2 to hydroxyl radicals. Density functional theory calculations indicate that strong electronic coupling among the metal components enhances catalytic efficiency by promoting charge transfer via d-orbital redistribution near the Fermi level. Leveraging these properties, we developed a colorimetric platform for rapid and sensitive detection of biothiols, acetylcholinesterase, and organophosphorus pesticides. Furthermore, by embedding HEzymes within an alginate hydrogel and integrating smartphone imaging, we further established a portable, rapid, and visual on-site biosensing platform. This approach expands the applicability of HEzymes in biosensing and medical diagnostics while offering new insights into their catalytic mechanisms and paving the way for next-generation biosensing technologies.