Versatile Conductive Polydopamine via Tailoring Counterions

Polydopamine (PDA), a synthetic analogue of natural biopolymer melanin, possesses a conjugated backbone that theoretically offers conductive pathways. However, the synthesis of conductive PDA has proven to be challenging, with only a few studies successfully achieving structural control during polymerization. In this study, the electrochemical synthesis of conductive PDA using various counterions, including lithium perchlorate (LiClO₄), potassium hexafluorophosphate (KPF₆), sodium <i>p</i>-toluene sulfonate (Na⁺-pTS), iron <i>p</i>-toluene sulfonate (Fe³⁺-pTS), and sodium polystyrenesulfonate, was systematically investigated in terms of their effect on the surface morphology, chemical structure, and electrochemical properties of PDA. To our knowledge, this is the first study to explore the role of counterions during the electropolymerization of PDA, resulting in significant improvements in its structure, hence the electrochemical performance. These findings suggest that the incorporation of counterions can pave the way for developing conductive PDA, which can be tailored for a wide range of bioelectronic applications.