Fluorescent sensors are ideal for biological applications due to their low invasiveness and miniaturizability. However, signal interference from autofluorescence and scattering limits their practical application. Long-lifetime phosphorescent materials have emission lifetimes on the order of hours or even days, and have long been used commercial in street signs and âglow-in-the-darkâ materials. More recently these materials have attracted interest as agents for biological imaging and sensing as a method for reducing background noise, since, by programming a delay between excitation and emission collection, the short-lived signals from scattering and autofluorescence can be avoided completely. In this work we demonstrate an ionophore-based optical sensor incorporating long-lifetime phosphorescent microparticles for background-free sodium detection in biological samples. We couple the phosphorescent microparticles to a pH-sensitive quencher dye and sodium-binding ionophore to create a dynamic and reversible optode film selective for sodium. We also characterize the sensor in terms of selectivity and stability and demonstrate its usefulness to detect sodium levels in human serum.
