Paper-Based Electrochemical Approach for Highly Rapid and Sensitive Quantification of Inorganic Phosphate in Freshwater

Rapidly monitoring dissolved inorganic phosphate is important for risk prediction and early warning of eutrophication. In this work, a reagentless electrochemical paper-based analytical device (ePAD) was developed to construct an environmentally friendly electrochemical platform for sensitively quantifying trace-level inorganic phosphate in freshwater. By modifying a type of self-synthesized nanocomposite material (zirconium dioxide/zinc oxide/multiwalled carbon nanotubes, ZrO₂–ZnO/MWCNTs), more abundant electroactive sites on the paper-based electrode surface were provided for the efficient adsorption of inorganic phosphate. The voltammetric signal response for aqueous phosphate anions was notably enhanced relative to that obtained at bare ePADs by relying on reductive cyclic voltammetry with molybdate(VI). After optimizing the main experimental parameters, a lower detection limit of 0.7 μM with good linear correlation in the range of 1.43–50 μM was realized at ZrO₂–ZnO/MWCNTs/ePAD. Fast analysis time and good recovery percentages (105.64, 88.27, and 112.99%) were achieved in detecting inorganic phosphate from authentic freshwater samples (tap, runoff, and lake water). Owing to the ideal reproducibility and long storage stability of ZrO₂–ZnO/MWCNTs/ePAD, this user-friendly and low-cost device is promising to be an in situ portable sensor to detect inorganic phosphate in aquatic ecosystems.