Highly Conductive Polydopamine Coatings by Direct Electrochemical Synthesis on Au

Polydopamine (PDA) is a promising melanin-like material with unique properties such as hybrid electronic–ionic conductivity, UV–vis light absorption, wet adhesion, biocompatibility, anti-inflammation, and metal ion chelation. Despite its versatility, PDA has limited utilization in bioelectronics due to its low electrochemical conductivity. Here, we present an electrochemical synthesis for highly conductive PDA composites directly coated on Au electrodes. PDA was deposited by the confined oxidizing effect of dissolved Au3+ on the electrode, which produced unprecedentedly conductive PDAs. The impedance of the Au electrode decreases by 2 orders of magnitude at 1 kHz, and both the ionic charge storage capacity and the safe charge injection limit increase by 1 order of magnitude, respectively. Unlike conventional conducting polymers, the PDA composite provides durable electrochemical performances after 1000 cyclic voltammetry (CV) cycles between −0.6 and 0.8 V. Furthermore, the PDA/Au showed remarkable structural modulation from fluffy to dense PDA as well as the efficient charge-transfer capability for both cationic and anionic carriers compared to the Au electrode. This unique PDA composite can be used as a conductive bioorganic material to develop edible/implantable/biodegradable electrodes, biosensors, and neuromorphic electrochemical devices for future bioelectronic applications.