Dopamine−Melanin Film Deposition Depends on the Used Oxidant and Buffer Solution

Abstract

The deposition of "polydopamine" films, from an aqueous solution containing dopamine or other catecholamines, constitutes a new and versatile way to functionalize solid-liquid interfaces. Indeed such films can be deposited on almost all kinds of materials. Their deposition kinetics does not depend markedly on the surface chemistry of the substrate, and the films can reach thickness of a few tens of nanometers in a single reaction step. Up to now, even if a lot is known about the oxidation mechanism of dopamine in solution, only little information is available to describe the deposition mechanism on surfaces either by oxidation in solution or by electrodeposition. The deposition kinetics of melanin was only investigated from dopamine solutions using oxygen or ammonium persulfate as an oxidant and from a tris(hydroxymethyl) aminomethane (Tris) containing buffer solutions at pH 8.5. Many other oxidants could be used, and the buffer agent containing a primary amine group may influence the deposition process. Herein we show that the deposition kinetics of melanin from dopamine containing buffers at pH 8.5 can be markedly modified using Cu(2+) instead of O2 as an oxidant: the deposition kinetics remains linear up to thicknesses of more than 70 nm, whereas the film growth stops at 45 ± 5 nm in the presence of 02. In addition, the films prepared from Cu(2+) containing solutions display an absorption spectrum with defined peaks at 320 and 370 nm, which are absent in the spectra of films prepared in oxygenated solutions. The replacement of Tris buffer by phosphate buffer also has a marked effect on the melanin deposition kinetics.

Deposition Mechanism and Properties of Thin Polydopamine Films for High Added Value Applications in Surface Science at the Nanoscale

“…Of the highest interest is that the deposition of polydopamine occurs at a pH of about 4 when ammonium persulfate is the oxidant. The same finding holds true when copper (II) sulfate is the oxidant [52]. These findings show that some fundamental investigations about the oxidation mechanism of dopamine into dopamine quinone, which is known to be a pH-dependent equilibrium, are necessary (Scheme 2).…”

Surface-independent one-pot chelation of copper ions onto filtration membranes to provide antibacterial properties

“…17 Therefore, the copper chelated on the PDA deposited membrane surfaces was mostly in the form of Cu 2+ and Cu + , and no metallic copper was found, which is consistent with the previous study. 18 To understand the role of Cu 2+ in the polymerization of DOPA solution, UV-VIS was used to monitor the formation of PDA having a characteristic absorbance peak at 420 nm. 16 When DOPA solution was acidic at pH 4.5, as shown in Figure S5, there was no absorbance detected at 420 nm and no color change observed in air with the absence of Cu 2+ , which has been reported that DOPA could not selfpolymerize at acidic condition.…”

Changes in Permeability and in Mechanical Properties of Layer-by-Layer Films Made from Poly(allylamine) and Montmorillonite Postmodified upon Reaction with Dopamine

“…This suggests that the polydopamine deposited in the (PAH-MMT) 10 film is much important than the *35 nm thick layer grown on quartz in these conditions [34]. Even if the reaction time of 14 h between the film and the oxygenated dopamine solution may not be sufficient to fill the film homogenously with polydopamine through its whole thickness, it was nevertheless sufficient to significantly modify the properties of the (PAH-MMT) n films, as will be shown below.…”