The Photophysics and Photochemistry of Melanin‐ Like Nanomaterials Depend on Morphology and Structure

Abstract

Melanin-like nanomaterials have found application in a large variety of high economic and social impact fields as medicine, energy conversion and storage, photothermal catalysis and environmental remediation. These materials have been used mostly for their optical and electronic properties, but also for their high biocompatibility and simplicity and versatility of preparation. Beside this, their chemistry is complex and it yields structures with different molecular weight and composition ranging from oligomers, to polymers as well as nanoparticles (NP). The comprehension of the correlation of the different compositions and morphologies to the optical properties of melanin is still incomplete and challenging, even if it is fundamental also from a technological point of view. In this minireview we focus on scientific papers, mostly recent ones, that indeed examine the link between composition and structural feature and photophysical and photochemical properties proposing this approach as a general one for future research.

Enhanced photochemical activity and ultrafast photocarrier dynamics in sustainable synthetic melanin nanoparticle-based donor–acceptor inkjet-printed molecular junctions

“…More phototoxicity has been reported for pheomelanin compared to eumelanin. 55,56 Our photocatalysis experiments are conducted at longer wavelengths (460 nm) and we still see some photoactivity in the degradation of MB pigments for melanin nanoparticles. By anchoring melanin to TiO 2 (a biocompatible pigment) the photoactivity is even improved.…”

Recent Applications of Melanin-like Nanoparticles as Antioxidant Agents

“…Although the AOX properties of natural melanin are well documented [ 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 ], and in addition to the ubiquitous presence of melanin in nature, its most recent and promising application is based on the development of synthetic analogs [ 78 ]. The main reason for this is that melanin-like materials can be easily produced from low cost and biocompatible precursors via very versatile and environmentally friendly processes [ 79 , 80 ]. Importantly, melanin synthetic analogues maintain the intrinsic biocompatibility of the natural pigments.…”

“…PDA is typically produced in the form of NPs and it has been reported to present good AOX properties [ 55 , 81 , 82 ]. We would like to stress that due to their high biocompatibility and dispersibility in physiological media, melanin-like NPs can be typically directly administered to organisms for bio-application purposes without requiring any delivery platform, being also themselves good vectors for the delivery of other bioactive agents [ 79 , 80 ].…”

The Anodization of Thin Titania Layers as a Facile Process towards Semitransparent and Ordered Electrode Material

“…Going towards the nanodimensions we can identify the properties that have not been reported for the macroscale [ 11 ]. It may seem strange that having the same chemical formula, like pure gold, silver, titanium dioxide or iron oxide, the control over the morphology can lead to the completely different properties [ 12 ]. Despite we have the limited number of abundant elements and easy accessible compounds; one can produce nanomaterials with unique properties basing on the same substrate.…”