Self-Referenced Scanning Ion Conductance Microscopy for Bath Solution-Flexible Imaging

Scanning ion conductance microscopy (SICM) has emerged as a powerful tool for high-resolution, in situ imaging in liquid environments, widely used in biomedical and materials science. Conventional SICM relies on identical electrolyte concentrations inside and outside the nanopipette to maintain stable ionic current signals, constraining its applicability under asymmetric or electrolyte-free bath conditions. To address this limitation, we developed a modified single pipette-based self-referenced SICM (SR-SICM), which enables high-resolution imaging in solvent-flexible environments. By coating the nanopipette exterior with silver to serve as an integrated reference electrode, the ionic current circuit is confined to the probe tip, effectively eliminating interference from the external bath. Finite Element Method (FEM) was employed to elucidate SR-SICM operation and optimize parameters. Simulations revealed a nonmonotonic current-distance profile arising from the competing effects of localized ion enrichment and restricted ion transport, especially under electrolyte-free conditions. Experimental validation confirmed the dual-phase behavior, resulting in an extended feedback range compared to conventional SICM. Imaging of poly(dimethylsiloxane) (PDMS) structures and biological samples demonstrated the robustness and versatility of SR-SICM across diverse solvent systems. This approach significantly broadens the operational scope of SICM, enabling stable, high-resolution imaging in environments previously inaccessible to conventional systems.