Polymerization of dopamine catalyzed by laccase: Comparison of enzymatic and conventional methods.

Polydopamine (PDA) films are generally produced by spontaneous oxidation of dopamine in basic medium, which is a highly convenient method for surface modification. This method is, however, not suitable for alkaline sensitive materials, which have poor stability in alkali medium and need over-long reaction time. Herein, we compared two dopamine polymerization methods: conventional method (induced by O2 at pH 8.5) and laccase-catalyzed method (at pH 5.5). The comparison showed that the polymerization of dopamine was greatly improved when catalyzed by laccase. The PDA film obtained from laccase-catalyzed method was more uniform and more stable compared with that obtained from the conventional method; the film was able to further react with amine-terminated molecules. As a result of laccase, ether bonds were found between dopamine units of PDA; while such bonds were not observed in film obtained from the conventional method. This work can be a basis for a better understanding of structure and property relationships of PDA coating.