A PAAM–PAAMPSA/PEDOT:PSS/CNTs-IL Multifunctional Hydrogel for Electrochemical Lactate Sensing and Piezoresistive Strain Monitoring

Flexible sensing devices have attracted substantial attention due to their unique advantages and have become indispensable components in emerging applications, such as wearable technology, health monitoring, and intelligent systems. The development of multifunctional materials has been identified as a critical driver for the advancement of next-generation flexible sensors. This work presents a multifunctional hydrogel based on poly(acrylamide)-poly(2-acrylamido-2-methyl-1-propanesulfonic acid)/ionic liquid-functionalized carbon nanotubes/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate), (PAAM–PAAMPSA/CNTs-IL/PEDOT:PSS), denoted as PPC, which demonstrates a dual sensing modality. When applied as an electrochemical lactate sensor, PPC exhibits high sensitivity with a low detection limit of 0.34 μM and excellent linearity (R2 = 0.9967) across the concentration range of 1–30 mM in phosphate buffer solution. Furthermore, its electrochemical performance is minimally affected by mechanical deformation, confirming that the interference from incidental strain is negligible. The hydrogel also functions effectively as a strain sensor, demonstrating excellent sensitivity (gauge factor = 1.44) and fast response (550 ms), and consistent performance over 1000 cycles at 100% strain. In summary, the PPC hydrogel developed in this study has the dual functions of sweat lactic acid sensing and stable strain monitoring, making it a promising material in the field of multifunctional wearable devices.