Chemical vapor deposition - based synthesis of conductive polydopamine thin-films

Polydopamine (PDA) represents a family of synthetic bio-inspired pigments offering high functional activity combined with semiconducting properties. To date, it represents one of the main synthetic biopolymers used mainly because of its simple synthesis in aqueous solutions. Thereby dopamine polymerizes in the presence of ambient oxygen to polydopamine. However, its structure renders a sophisticated backbone relating to variations of ambient growth parameters such as temperature, local pH and partial oxygen pressure; preponderant repeating units found in aqueous polydopamine are 5,6-hydroxyl-indole derivatives. However, hydrogen-bonded aggregation competes with the polymerization leading to complex systems. In order to reduce the aggregation we hypothesized that acidic oxidants will direct the polymerization towards C-C coupling and hence create synthetic biopolymers. In this work we demonstrate oxidative chemical vapor deposition (o-CVD) for PDA, where we obtain the desired consistent biopolymer thin-films as shown by structural analysis. Furthermore, as-gained polydopamine is conductive and renders fingerprint signatures of free charge carriers. Concomitantly it preserves its functionality - imperative for potential applications in catalysis or as bio-linker.