<i>In Situ</i> Functionalized MXene on Porous Laser-Induced Graphene for Adsorption-Dominated Miniaturized Multifunctional Sensors

Despite the rapid advancement of multifunctional wearable sensors for health monitoring, they often suffer from significantly reduced sensitivity and stability when they are reduced in size for miniaturization. This study explores a two-step direct laser writing process to introduce <i>in situ</i> functionalized MXene with reduced surface terminating groups on highly porous laser-induced graphene foam, shifting the electrochemical reaction from the traditionally diffusion-controlled to the new adsorption-controlled. The resulting highly stable nanocomposite also addresses the oxidation issues of MXene. As a result, the electrochemical sensor exhibits enhanced sensitivity from 242.78 to 2751.3 μA/mM·cm² to glucose, as the electrode radius is reduced from 2.5 to 0.5 mm. The sensor also exhibits a low limit of detection of 0.3 μM, a rapid response time of 0.1 s, and excellent stability over 35 days in ambient conditions. The nanocomposite can also be explored in a humidity sensor with high sensitivity and rapid response/recovery time, along with the dry electrophysiological electrodes with increased amplitude and signal-to-noise ratio, even in the presence of sweat. The miniaturized size of the sensors further allows seamless integration of multiple sensing modalities with a virtual reality mask to monitor physical and mental conditions for the identification and evaluation of phobias.