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    A Clean and Tunable Mussel-Inspired Coating Technology by Enzymatic Deposition of Pseudo-Polydopamine (psi-PDA) Thin Films from Tyramine

    Year: 2020

    Journal: Int. J. Mol. Sci., Volume 21, JUL

    Authors: Alfieri, Maria Laura; Panzella, Lucia; Arntz, Youri; Napolitano, Alessandra; Ball, Vincent; D'Ischia, Marco

    Keywords: polydopamine; tyramine; tyrosinase-catalyzed oxidation; low-waste coating technology; atomic force microscopy; MALDI-MS; water contact angle; cyclic voltammetry

    The tyrosinase-catalyzed oxidation of tyramine, leading to the deposition of pseudo-polydopamine (psi-PDA) thin films, is disclosed herein as a superior technology for surface functionalization and coating at a neutral pH and at a low substrate concentration, compared to the standard autoxidative PDA coating protocols. Smooth psi-PDA thin films of variable thickness up to 87 nm were obtained from 1 mM tyramine by varying tyrosinase concentrations (5-100 U/mL). Compared to the PDA films obtained by the similar enzymatic oxidation of 1 mM dopamine with tyrosinase (T-PDA), psi-PDA displayed slower deposition kinetics, lower water contact angles in the range of 11 degrees-28 degrees, denoting higher hydrophilicity but similar UV-vis absorption profiles, as well as electrochemical properties and antioxidant activity. MALDI-MS analysis indicated for psi-PDA a well defined pattern of peaks compatible with dopamine tetrameric structures degraded to a variable extent. The exposure to a tyramine solution of tyrosinase-loaded alginate spheres, or films deposited on glass or polyethylene, resulted in a rapid gel-confined psi-PDA formation with no leakage or darkening of the solution, allowing the complete recovery and re-utilization of the unreacted tyramine. In contrast, an abundant PDA precipitation outside the gel was observed with dopamine under the same conditions. The psi-PDA deposition by tyrosinase-catalyzed tyramine oxidation is thus proposed as a controllable and low-waste technology for selective surface functionalization and coating or for clean eumelanin particle production.
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