Paper-based ion-selective optodes for continuous sensing: Reversible potassium ion monitoring.

A simple, low-cost paper-based potassium ion-selective optode that exhibits fully reversible sensing properties is presented. A classic optode formulation consisting of valinomycin as the ionophore and a lipophilic pH indicator has been successfully transferred to a paper substrate and characterised in a flow-through cell with reflectometric optical detection. The optode exhibits high repeatability, reversibility, and stability and can detect potassium in the physiologically relevant concentration range from 10 to 10 M.