Portable Paper-Based Sensing Platform for Rapid and Simultaneous Measurement of Environmental pH and Soluble Reactive Phosphorus.

Accurate detection of bioavailable phosphorus (BP) is critical to mitigate freshwater eutrophication from excess phosphorus, but quantifying trace soluble reactive phosphorus (SRP) under real-world pH remains challenging. We present a portable paper-based electrochemical sensor for simultaneous SRP and pH monitoring in agricultural water. The platform establishes dual linear correlations: peak current-SRP concentration (LOD < 2 μM) and peak potential-pH (1-7) via square wave voltammetry (SWV). This enables micromolar-level SRP quantification across an environmentally relevant pH range with minimal interference. Field validation in farmland solutions demonstrates direct differentiation of dissolved and colloidal phosphorus fractions without pH alteration, overcoming the limitations of conventional methods. This work provides a powerful tool for in situ environmental monitoring, offering new insights into P bioavailability and advancing sustainable nutrient management in diverse agricultural contexts.