Computational modeling and experimental validation of the photothermal activity of metal-ion chelated natural melanin nanoparticles

Melanin, a naturally occurring biopolymer, serves as a pigment and protective agent in organisms such as animals, fungi, and bacteria. Melanin nanoparticles, which can be obtained naturally or synthetically, are frequently investigated in many biomedical applications due to their high biocompatibility, biodegradability, antioxidant properties, and visible light absorption properties. In addition, the chemical structures of melanin nanoparticles allow them to chelate drugs, various biomolecules, and metal ions such as Fe3+, Cu2+, Gd3+, Mn2+. It has been shown that melanin nanoparticles chelated to metal ions can also be used as a contrast agent by shortening the T1 relaxation time in magnetic resonance imaging. With these properties, melanin nanoparticles are being investigated for both imaging and treatment, i.e. theranostic purposes. However, the effect of nanoparticle size and the wavelength of the applied light on PTT efficiency, as well as the impact of metal ion chelation of melanin nanoparticles on photothermal performance, has not been comprehensively investigated in the literature, to the best of our knowledge. This study aims to investigate these effects through modeling and in vitro experiments. Answering these questions will enable the determination of the most appropriate nanoparticle size and irradiation parameters, and will pave the way for temperature-controlled PTT applications and optimization of treatment efficiency.