Ion Identification\nand Ultralow Concentration Sensing\nwith Liquid Flexoelectricity

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