Combining Electrochemistry with Spontaneous Microfluidics for Robust Membrane-Free Gas Sensing with Ionic Liquid Electrolytes
Electrochemical gas sensing is a low-cost and rapid way to detect gases in the atmosphere, with various devices including amperometric gas sensors (AGSs) being developed for this purpose. However, it is challenging to achieve miniaturization and fast response times with the traditional AGS design because of the use of a membrane. Room temperature ionic liquids (RTILs) have been proposed to overcome these challenges because of their nonvolatility, allowing for the removal of the membrane; however, there are still limitations with the use of liquid electrolytes due to stability and robustness when the sensor is employed in different electrode orientations. In this work, we have combined platinum wicking membrane interdigitated electrodes (WM-IDEs) with RTILs to produce thin films of solvent with uniform thickness (30 μm) over the whole electrode. Three gases—oxygen, ammonia, and sulfur dioxide—were successfully detected at analytically relevant levels using cyclic voltammetry and chronoamperometry on these devices, with stable and reproducible responses observed over long periods of time. In particular, the best responses were observed for oxygen using long-term chronoamperometry with very fast response times of <4 s, faster than other miniaturized designs. This platform may be further modified and adapted to detect other air pollutants or volatile organic compounds in breath for health monitoring.