Aerosol jet printing of polyelectrolyte-modified MXene ink for a multifunctional humidity and temperature flexible sensor

MXenes have emerged as a highly promising material for next-generation patterned flexible sensing devices owing to their exceptional electrical conductivity, biosafety, and processability. In this study, we present a facile polyelectrolyte-assisted aerosol jet printing (AJP) strategy for fabricating MXene-based flexible sensors with largely improved printing quality for the applications in humidity and temperature sensing. By leveraging the electrostatic interactions network between sodium alginate (SA)-modified MXene ink and a chitosan (CS) substrate, the sensor achieves densely and stably packed MXene nanosheets with minimized defects. The intercalated SA molecules not only improve printing quality of AJP, but also enhance the humidity and temperature sensitivity of the MXene/SA patterns by modulating the interlayer spacing and functional groups within MXene layers. The resulting MXene/SA@CS sensor achieves a temperature coefficient of resistance (TCR) of 1.08% °C −1 (30–110 °C) and exhibits real-time responses to humidity changes from human motions with the largest 356 ± 9% resistance response rate and the shortest rapid response/recovery times (0.30 s/2.00 s). Its excellent antimicrobial properties and biocompatibility highlight the potential for wearable health monitoring and human-machine interfaces. Finally, the AJP-printed MXene sensors with programmable structures were successfully applied as a noncontact controller via finger movement detection.