Photoelectroactive Composites Based on PPy-MXene/PDA for Multifunctional Bioelectronic Interfacing

The emerging two-dimensional material, MXene, has attracted widespread interest in bioelectronic interfaces due to its outstanding optical, electrical, and chemical properties. However, current in situ fabrication strategies have not fully achieved robust MXene-based bioelectrodes, significantly limiting their functionalities and applications. Here, we present an electropolymerization and codeposition approach to combine the negatively charged MXene nanosheets, positively charged pyrrole (Py) radical cations, and polydopamine (PDA) adhesion elements. The as-prepared PPy-MXene/PDA composites as an bioelectrode exhibits a dramatically reduced interfacial impedance of ∼99% in the low-frequency region, a cathodic charge storage capacity (CSC_c) up to 195 mC cm^-2, and record-high charge injection capacity (CIC) of 15 mC cm^-2. No significant delamination or electrochemical loss is observed even after being subject to continuous electrostimulation, long-term immersion, and high-frequency mechanical stimulation in phosphate-buffered saline (PBS), showing robust chronic stability. Moreover, the bioelectrode demonstrates a high, rapid, and stable photoelectrochemical response under near-infrared laser irradiation. The PPy-MXene/PDA-based photoelectroactive composites also exhibit excellent sensitivity to ascorbic acid, with a detection limit an order of magnitude lower than that of pure MXene. The mechanism underlying the enhanced performance of the PPy-MXene/PDA bioelectrode is systematically studied. This PPy-MXene/PDA-based photoelectroactive composites can be extended to numerous other applications.