Improving Electrochemical Sensing in Ionic Liquid Droplets via Microscale Stirring

In the field of ionic-liquid-based electrochemical gas sensors, the high viscosity of ionic liquids leads to slow mass transfer, restricting sensor performance. In this study, microstirbars with tunable sizes were fabricated via wet spinning. Using fluorescent dye as a tracer, these microstirbars homogeneously dispersed the dye in a droplet of ionic liquid within 2 min, nearly 200 times faster than the control group without stirring. When using ferrocene as a model reactant in chronoamperometry, the microstirbars enhanced the mass transfer process and the best stirring conditions (400 rpm, 8.0 wt %, <i>l</i> = 300 μm) were determined. When these optimized conditions were applied to oxygen detection, the results showed that the sensor sensitivity reached 0.63 μA·%^-1, on par with the best performing gas sensors in the literature and 6 times higher than the control group without stirring. The stirred sensor achieved <i>T</i>₉₀ of 7.0 s for 6.7% O₂, three times faster than that of the control group without stirring (21 s). This study presents a straightforward approach to addressing the mass transfer challenges in ionic liquids, serving as a viable alternative to the complex designs of electrochemical sensors. As an approach to enhance mass transfer in microdroplets, we believe that the microstirring strategy is not limited to gas sensors. With advances in miniaturization of electromagnetic devices, it holds promise for a variety of sensing schemes.