Single Liquid Aerosol Microparticle Electrochemistry on a Suspended Ionic Liquid Film

Liquid aerosols are ubiquitous in nature, and several tools exist to quantify their physicochemical properties. As a measurement science technique, electrochemistry has not played a large role in aerosol analysis because electrochemistry in air is rather difficult. Here, a remarkably simple method is demonstrated to capture and electroanalyze single liquid aerosol particles with radii on the order of single micrometers. An electrochemical cell is constructed by a microwire (cylindrical working electrode) traversing a film of ionic liquid (1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide) that is suspended within a wire loop (reference/counter electrode). An ionic liquid is chosen because the low vapor pressure preserves the film over weeks, vastly improving suspended film electroanalysis. The resultant high surface area allows the suspended ionic liquid cell to act as an aerosol net. Given the hydrophobic nature of the ionic liquid, aqueous aerosol particles do not coalesce into the film. When the liquid aerosols collide with the sufficiently biased microwire (creating a complex boundary: aerosol|wire|ionic liquid|air), the electrochemistry within a single liquid aerosol particle can be interrogated in real-time. The ability to achieve liquid aerosol size distributions for aerosols over 1 mu m in radius is demonstrated. While stochastic electrochemistry has been used for decades to detect and analyze many types of single entities (e.g., nanoparticles, bacteria, and microdroplets) these "things" have been suspended in a liquid phase. Here, a method capable of electrochemically detecting intact liquid aerosols, one-at-a-time, is provided. This allows electrochemical access to the air|microdroplet interface, which has been shown to be incredibly important for chemical reactivity in microdroplets. image