Determination of the extinction coefficient of polydopamine films obtained by using NaIO4 as the oxidant

Understanding the molecular origin of the broadband optical absorption spectrum of eumelanin in solution remains a challenging task both from an experimental and a theoretical point of view. Eumelanin like materials can now be deposited on solid surfaces from dopamine solutions in oxidizing conditions allowing to easily functionalize the surface of almost all materials. The optical spectra of those poly dopamine (PDA) films are close to the spectra of eumelanin but not identical. This article is a first attempt to quantify the optical absorption coefficient of PDA films which is made complicated by the uncertainty due to the need to know the density of this material. Using dissolved NaIO4 as the oxidant, at 0.5,1 or 10 mM, the film thickness versus time does superimpose with the absorbance versus time curves suggesting intrinsic film homogeneity and allowing to calculate the product of the extinction coefficient by the concentration of PDA in the film. (C) 2016 Elsevier B.V. All rights reserved.