Gadolinium-doped carbon nanoparticles: coordination, spectroscopic characterization and magnetic resonance relaxivity

Abstract

Carbon nanoparticles (CNPs) are attracting great attention as potential multifunctional agents for biomedical applications because of their bright fluorescence, low toxicity and flexibility of the physico-chemical properties. In the present paper, aqueous solutions of CNPs doped with gadolinium (Gd) (Gd-CNPs) in a wide range of Gd-concentration were prepared by hydrothermal synthesis. The role of Gd doping on the optical properties and magnetic resonance (MR) relaxivity of Gd-CNPs was revealed. The Gd content was determined using X-ray fluorescence and spectrophotometry analysis. The composition of surface functional groups and coordination of Gd-ions in Gd-CNPs were established by means of the IR absorption spectroscopy and X-ray photoemission spectroscopy (XPS). The optical properties of Gd-CNPs in aqueous solutions were characterized by means of the UV-visible-near-IR absorption spectroscopy and photoluminescence measurements with different excitation wavelength. The local surroundings of Gd-ions and paramagnetic centers in Gd-CNPs were probed by using the electron paramagnetic resonance (EPR) spectroscopy. The MR proton relaxation measurements in aqueous solutions Gd-CNPs were carried out to determine the role of Gd-concentration for their MR contrasting. The obtained results characterize the coordination of Gd ions in Gd-CNPs and demonstrate new visions for controlling the optical and MR contrast properties of these nanoparticles for biomedical applications.