Nanozymes on paper: Transforming microfluidic devices for portable biosensing

Paper-based microfluidic analytical devices (μPADs) form a hydrophilic channel by patterning a hydrophobic barrier, and use capillary action to achieve pumpless fluid control. As point-of-care testing (POCT) platforms, they have significant advantages such as low cost, ease of operation, and low sample consumption compared with traditional microfluidic chips. They are especially suitable for biomarker detection in resource-limited areas and home healthcare settings. To overcome the high cost and environmental instability of traditional natural enzymes as biorecognition elements, redox nanozymes with peroxidase (POD)-like activity have become a stable and economical alternative. Through the synergistic combination of physical adsorption and in situ growth techniques, nanozyme-μPAD constructs offer expedited, user-friendly detection capabilities for a broad spectrum of analytes, encompassing disease biomarkers, pathogenic agents, and environmental pollutants. This article reviews the research progress of the functional transformation of μPADs through the integration of nanozymes, systematically discusses the categories, design, screening, and regulation strategies of nanozymes, and elaborates on their catalytic mechanism in signal amplification. The article focuses on the key applications of nanozyme-functionalized μPADs in the fields of biomedical diagnosis and food safety detection, and outlines future development trends, existing challenges, and potential research directions of this technology.