Recent progress in sensing nitrate, nitrite, phosphate, and ammonium in aquatic environment

Aquatic chemical sensors have experienced rapid development in recent years largely due to advances in the fields of nanotechnology. Accurate in situ monitoring of nutrients is fundamental to understanding the biogeochemistry of aquatic ecosystems and is necessary for the sustainable utilization of water resources. Although many sensor technologies can achieve nM detection levels, quality assurance and reliability for long-term sensing in complex environments is still lacking. Furthermore, some sensors suffer from sensitivity to high background ion concentration. This review aims to address these challenges by highlighting recent improvements in aquatic chemical sensors to monitor nitrate (NO₃⁻), nitrite (NO₂⁻), ammonium (NH₄⁺), and phosphate (PO₄³⁻) ion concentrations in water. The review critically analyses and compares the performance of these chemical sensors with a particular emphasis on their capability for long-term in situ water monitoring. We also provide an overview on some crucial problems significantly affecting the analytical performance of the sensors. Finally, this review details some recommendations and future directions for improving sensing accuracy and robustness.