Synthesis of melanin-based nanoparticles for light absorption and photothermal effect

Abstract

Melanin is a natural pigment that determines the color of hair, eyes and skin. It absorbs light of various wavelengths, from ultraviolet to visible and near infrared. Melanin strongly absorbs light in the ultraviolet range and suppresses the production of active oxygen by ultraviolet rays. In addition, the self-assembly of melanin nanoparticles imparts a unique structural color. Some reptiles are known to use melanin to convert light into heat energy to regulate body temperature. Melanin nanoparticles are attractive materials for a wide range of applications including sunscreen, pigmentation and photothermal therapy. However, natural melanin nanoparticles are severely aggregated or have non-uniform size and shape, which limits processing and application. In this study, two types of melanin-based nanoparticles were synthesized. First, several nanometer-sized eumelanin nanoparticles were synthesized by self-polymerization of L-dopa. Second, polydopamine nanoparticles were synthesized by self-polymerization of dopamine, and L-dopa having a stronger negative charge was added to coat the surface of the polydopamine nanoparticles with eumelanin. The synthesized particles are intended to be applied to improving structural color saturation, diagnostic kits, and photothermal therapy.