Rhodamine dye transfer from hydrogel to nanospheres for the chemical detection of potassium ions

Abstract

Smart hydrogels incorporating various functional nanomaterials are becoming popular tools for chemical sensing. Here, ion-exchange nanospheres composed of the block copolymer Pluronic F-127 played the role of a scavenger for a signal transducer dye (Rhodamine 800) in a three-phase based optical detection system for potassium ions. Rhodamine 800, a positively charged dye, was incorporated into a hydrogel together with the potassium ionophore valinomycin and an ion-exchanger (Na⁺R⁻). The concentration of Rhodamine 800 in the aqueous sample was kept low by the nanospheres containing Na⁺R⁻. Consequently, the detection limit (0.3 μM) of the three-phase based system was shifted 2 orders of magnitude lower compared with those of previously reported two-phase based sensing systems. The concept of controlling the dye transfer among the three phases provided a new train of thought for the design of ionophore-based chemical sensors.