Modular Europium-Based Nanosensors for the Detection of Sodium and Potassium Ions

In this work, we demonstrate a modular approach to ion detection using europium (Eu) chelates as luminescent reporters in Na⁺- and K⁺-selective nanosensors. We evaluated a commercially available option (Eu-(DBM)₃Phen) and synthetically derived options (Eu-(tacn-PEPA₃) and Eu-(DBM)₃Bipy). The sensors exhibited reversible, tunable, and selective responses to their target ions, even in the presence of biologically relevant competing species. Furthermore, Eu-(DBM)₃Phen showed no degradation when the O₂ concentration was varied (0-21%) but showed limitations, including a shorter luminescence lifetime (131 μs), pH sensitivity, and susceptibility to interference from divalent cations. In contrast, Eu-(tacn-PEPA₃) offered a longer lifetime (549 μs), greater pH stability, and reduced ionic interference. To validate platform modularity, the chromoionophore in the sodium sensor was successfully replaced with an alternative dye (BB-dye), confirming that the gating mechanism depends on the chromoionophore selection. These findings underscore the potential of Eu-chelates for biocompatible, time-gated ion sensing, with future work focused on enhancing stability, minimizing pH sensitivity, and shifting excitation wavelengths into the NIR-II region to support in vivo imaging applications.