Comparison of Photothermal Activity of Iron- and Manganese-Chelated Natural Melanin Nanoparticles

Abstract

Melanin is a pigment abundance in many living organisms and has been studied for its nanoparticle form in applications such as biosensors, drug delivery, imaging, and photothermal therapy. Previous research indicated that natural melanin nanoparticles (MNPs) conjugated with metal ions could serve as contrast agents for T1-weighted magnetic resonance imaging due to their high T1 relaxivity rates. MNPs have excellent ultraviolet (UV) and near-infrared irradiation absorption and photothermal activity in a wide range of wavelengths. This study investigated whether the photothermal properties of melanin nanoparticles persist after metal-ion chelation, comparing the efficacy of natural and metal-conjugated forms at different concentrations. The results demonstrate that metal ion chelation used for MR imaging does not affect the photothermal efficiency of MNPs, and the photothermal activity of the nanoparticles increase with nanoparticle concentration. The solution consisting of a 2 mg/ml concentration of manganese-MNP complexes (MNP-Mn2+) showed the highest increase with 7ºC temperature compared to distilled water under 633 nm wavelength laser irradiation for 30 minutes. © 2024 Elsevier B.V., All rights reserved.