Characterization of Polydopamine Thin Films Deposited at Short Times by Autoxidation of Dopamine

TLDR

Current interest in melanin films derived from the autoxidation of dopamine stems from their use as a universal adhesion layer. Here we report chemical and physical characterization of polydopamine films deposited on gold surfaces from stirred basic solutions at times ranging from 2 to 60 min, focusing on deposition times ≤10 min. FTIR, XPS, and electrochemical data reveal that polydopamine films contain starting dopamine and intermediate C=N‑tautomer species at all times, that film thickness increases linearly during the first 10 min, that films become largely continuous with surface roughness ≤2 nm after ≥10 min, and that pinhole‑free films require at least 60 min of deposition.

Abstract

Current interest in melanin films derived from the autoxidation of dopamine stems from their use as a universal adhesion layer. Here we report chemical and physical characterization of polydopamine films deposited on gold surfaces from stirred basic solutions at times ranging from 2 to 60 min, with a focus on times ≤10 min. Data from Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical methods suggest the presence of starting (dopamine) and intermediate (C=N-containing tautomers of quinone and indole) species in the polydopamine films at all deposition times. A uniform overlayer analysis of the XPS data indicates that film thickness increased linearly at short deposition times of ≤10 min. At deposition times ≥10 min, the films appeared largely continuous with surface roughness ≈ ≤ 2 nm, as determined by atomic force microscopy (AFM). Pinhole-free films, as determined by anionic redox probe measurements, required deposition times of 60 min or greater.