Electropolymerization of Bio-inspired Catecholamines for Electrochemical Sensors

Oxygen-driven polymerization of catecholamines is the current standard method to prepare biomimetic polymeric films onto virtually any type of surface, inspired on the adhesive properties of mussels to wet surfaces [1]. Polycatecholamine coatings have been used for a wide range of purposes including biofouling, self-healing, molecular imprinting and (bio)sensing applications [2]. The latter relies on the inherent reactivity of quinone moieties towards nucleophilic functions (thiols and amines) of aminoacids, through Michael addition or Schiff-base reactions. Recently, we have proved that chemically synthesized polydopamine thin films are suitable to immobilize biomolecules and to be employed as electrochemical transducers in enzymatic reactions [3]. Nevertheless, it is recognized that chemical growth of these type of polymeric films, yields heterogeneous and poorly conducting matrices. In this work we aim to overcome the problems of film heterogeneity, low conductivity and amount of quinone groups by producing biocompatible films through electropolymerization of dopamine (ePDA). In spite of the increasing interest in electrochemical synthesis [4], the mechanism of electropolymerization is still unclear and not yet entirely supported by experimental evidences. Hereby, we have synthesized potentiodynamic and potentiostatic ePDA films of different thickness and used a powerful combination of techniques (cyclic voltammetry, ellipsometry, UV-vis, IR and X-ray Photoelectron spectroscopy, goniometry and atomic force microscopy) to fully characterize their electrochemical and optical properties, wettability, morphology, thickness and chemical composition. Indeed, striking structural differences were observed for the ePDA films regarding the chemically synthesized polymers, unveiling distinct polymerization pathways. Further immobilization of enzymes in these polymeric matrices and their subsequent catalytic activity assessment by chronoamperometry, demonstrated a clear improvement of transducing performances when using the more electroactive ePDA films as support. The new structural insights presented in this work, undoubtedly prove the suitability of electrosynthesis to prepare organized and biocompatible polycatecholamines for biosensing and other electrochemical applications.