Water-Based Melanin Multilayer Thin Films with Broadband UV Absorption

Natural melanin is difficult to process due to its poor solubility and poorly understood structure. Synthetic melanin has been produced more recently, which is dispersible in mildly alkaline water and has many of the same properties of natural melanin. In this study, thin films of synthetic melanin and poly(allylamine hydrochloride) were deposited layer-by-layer from dilute aqueous solutions in ambient conditions. This is likely the first time melanin has been deposited from water to produce a functional nanocoating. These films display broadband UV light absorption, absorbing over 63% of incident light that is most damaging to human eyes with a thickness of 108 nm. In an effort to demonstrate the utility of these melanin-based nanocoatings, a 30 bilayer film is shown to increase the useful life of a conductive poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) film by 550%. This novel method of depositing melanin should open the door to a variety of useful applications.