New Method in Surface Treatment of Nanopipette for Interface between Two Immiscible Electrolyte Solutions (ITIES) Experiment

Interface between two immiscible electrolyte solutions (ITIES) is a powerful platform for chemical sensing and studying electron/ion transfer reactions and is typically formed between the interface of two immiscible solutions such as an oil phase and an aqueous phase. Micro/nano ITIES interface are generally formed at the tip of a borosilicate/quartz pipette, inner surface of which can be rendered hydrophobic to be filled with an organic solvent by a method called silanization. Nano/micrometer-sized electrodes are typically silanized by vapor silanization methods in which silanizing agent in vapor phase is exposed to nanopipettes. Micrometer-sized pipettes have been also silanized by directly filling liquid silanization agent, one type of liquid silanization methods, but this method has not been used at the nanoscale. Liquid silanization method allows to selectively silanize a single channel in a dual-channel pipette platform. Here, we developed the liquid silanization method for nanoscale ITIES and demonstrated that a stable cyclic voltammogram for tetrabutylammonium ion transfer across water/dichloroethane interface can be accomplished. We also presented challenges for liquid silanization at the nanoscale and strategies to overcome them. The liquid silanization methods presented here lay the foundation for future development of dual channel multi-functional probe where one channel is nanoITIES.