Electrochemical Phosphate Sensors With Sub‐Nanomolar Detection Limit Based on Selective and Reversible Europium( <scp>III</scp> ) Receptors

ABSTRACT Real‐time, continuous phosphate monitoring is vital in biomedical, agricultural, and environmental applications, yet most phosphate sensors are constrained by inadequate detection limits, poor selectivity, and irreversible binding. This work reports compact electrochemical devices that incorporate europium(III) complexes for sensitive phosphate detection, achieving sub‐nanomolar detection limits and enabling reversible binding for continuous monitoring. The sensors are highly selective over chloride and other competing anions. Two device architectures are developed and compared, where an amperometric configuration offers simple fabrication and an organic electrochemical transistor provides signal amplification. The sensors allow a wide linear dynamic range of 1–500 nM and a state‐of‐the‐art detection limit of 0.5 nM. The transduction mechanisms and operating parameters under different bias voltages, ionic strengths, and competing anions were systematically studied to optimize performance. The phosphate sensors are validated in complex media including artificial interstitial fluids and field samples from the Mississippi Sound. These results provide the design guidelines for electrochemical sensors using europium(III) complexes as low‐cost, portable, and regenerable platforms for biological and environmental monitoring. image