Biomimetic self-sustained ion oscillation in miscibility gap and chemical inductance impact in potassium sensing

A biomimetic potassium ion-selective electrode (ISE) was developed using a graphene oxide (GO)-coated nickel foam (NF) substrate functionalized with a polyethylene glycol (PEG)-based ion-selective layer (ISL). The sensing mechanism centers on a miscibility gap formed within the ISL due to PEG's amphiphilic nature when complexed with potassium iodide-driving phase separation into hydrophilic and hydrophobic domains. This phase heterogeneity introduces interfacial barriers that delay ionic relaxation and facilitate self-sustained ion oscillation, as evidenced by low-frequency inductive behavior in electrochemical impedance spectroscopy (EIS)-demonstrating a chemical inductor effect. The design eliminates the need for costly ionophores, such as valinomycin, presenting a scalable and cost-effective sensing platform. The sensor exhibited a linear response to K⁺ concentrations ranging from 0.5 to 10 mM, with a high sensitivity of 14.09 × 10² mA/mM·cm² and a detection limit of 0.69 mM. Selectivity tests showed minimal interference from Na⁺, Ca²⁺, urea, NH₄⁺, and ascorbic acid ions, and the sensor demonstrated excellent stability over 100 cycles. These findings provide a robust framework for developing low-cost, biomimetic electrochemical potassium sensing.