Ion Identification and Ultralow Concentration Sensing with Liquid Flexoelectricity.

The isolation and concentration of electrical charges at ionic-electronic interfaces are prevalent phenomena that impede effective communication between ionic and electronic systems. Detecting these concentrated charges at the interface is crucial for applications, such as signal transmission and ion detection. Current electrical detection approaches introduce additional ionic-electronic interfaces via metallic electrodes with an external stimulating voltage, which alters the initial ion distributions at the interfaces. In this work, we introduce the flexoelectricity of liquids to examine the electrical charge aggregation at ionic-electronic interfaces under cyclic mechanical loads. The measured electrical responses reflect the coupling phenomena between the flexoelectricity and the electric double layer. This proposed approach demonstrates the capability to quantify ion types and concentrations at interfaces. Furthermore, it can identify ion types in mixed solutions and offers high sensitivity at ultralow concentrations. This work promotes a nonchemical, general mechanical method for charge detection at ionic-electronic interfaces.