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 %, l = 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 T90 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.