Portable and Point-of-Care Testing Approach for Determining Soil Extracellular Enzyme Activities

Soil eco-enzymes (i.e., microbial extracellular enzymes) play essential roles in terrestrial nutrient cycling and support ecosystem services. In this regard, their activities serve as indicators of soil health. However, conventional spectrophotometric and microplate fluorometric assays are often limited by lengthy reaction procedures, relatively high reagent consumption, and insufficient compatibility with complex soil matrices. In this investigation, we developed a portable, centrifugally driven microfluidic chip for the rapid and sensitive determination of multiple soil extracellular enzyme activities. This integrated platform automated sample aliquoting, reagent metering, mixing, and sedimentation, enabling the parallel measurement of eight enzymes. Such system demonstrated precise liquid control via capillary valves and high optical uniformity (<5% fluorescence variation). 4-methylumbelliferone (MUF)-based calibration exhibited strong linearity (R² > 0.99) across diverse soil types. Compared with conventional microplate assays, the microfluidic method improved reproducibility (CV < 15%), enhanced the detection of weak fluorescence signals, and increased throughput while reducing reagent consumption. This field-ready platform provides a robust solution for standardized soil enzyme assessment and offers future potential for integration with AI-driven data analytics and large-scale ecological monitoring frameworks.