Microdroplet-Mediated Enzyme Activity Enhancement for Potentiometric Sensing of Peroxidase in Soil

On-site measurements of enzyme activity in complex solid matrices such as soil and sediment could offer invaluable insights for the soil health evaluation and sustainable management. As such, sensors for on-site measurements of soil enzyme activity are highly required but remain unachieved to date. Herein, a potentiometric sensor for rapid, direct, and in-field analysis of soil enzyme activity is proposed, in which soil particle separation and soil enzyme extraction can be achieved within a single device. More importantly, the enzyme activity mediated by microdroplets can be greatly enhanced for potentiometric measurements. By using a classic soil redox enzyme-peroxidase and an anti-interference substrate 3,3′,5,5′-tetramethylbenzidine as a model, the potentiometric sensor enables directly measuring peroxidase activity in the field with a detection limit that can reach as low as 10^–7 U mL^–1 within 5 min. Moreover, the potentiometric sensor was deployed for on-site analysis of the peroxidase activity of Suaeda salsa (L.) Pall. rhizosphere soil under salinity stress, showing excellent sensitivity and anti-interference capability, and retaining promising potential for evaluating the mechanisms and feedback in response to environment stresses.