  The spontaneous oxidation of dopamine in slightly alkaline solutions was
investigated on the basis of the work of Lee and others [Science, 318:426-430,
2007], and the reaction product was identified as dopamine-melanin. The ability
of melanin to covalently bind amine functional groups was confirmed by
quantification of the corresponding binding sites on dopamine-melanin
aggregates. Furthermore it is possible to redissolve dopamine-melanin
aggregates in strongly alkaline solutions. The obtained small melanin grains
were used to build layer-by-layer deposits with poly(diallyldimethylammonium).
  Different methods of dopamine oxidation to grow melanin films at
solid--liquid interfaces were developed. All examined methods lead to
continuous dopamine-melanin films with very similar surface morphologies. The
dopamine-melanin films become impermeable to electrochemical probes at a
thickness in the 10 nm range. In this context a higher permeability for
positively charged and neutral probes than for negatively charged ones was
confirmed for one preparation method.
  The adsorption of proteins on dopamine-melanin coatings was explained as
combination of electrostatic and strong, most probably covalent, interactions.
To obtain this explanation, the zeta-potential of dopamine-melanin deposits has
been measured as a function of pH.
  The formation of melanin by dopamine oxidation in layer-by-layer films of
poly(L-lysine) (PLL) and hyaluronate (HA) was studied: Melanin is able to
homogeneously fill $(\text{PLL-HA})_n$ films and the obtained
polyelectrolyte-melanin composites can be detached from their substrate as
free-standing membranes prepared by a biomimetic method in mild conditions.
