Gadolinium-doped carbon dots with long-wavelength emission for dual-modal imaging

Subject of study . This study is focused on luminescent carbon dots derived from o-phenylenediamine and gadolinium chloride or nitrate hexahydrate. Aim of study. The study aims to fabricate long-wavelength photoluminescent gadolinium-doped carbon dots that could function as contrast agents for magnetic resonance imaging. Additionally, the study investigates the impact of the precursor type used on the chemical composition and optical transitions of the resulting nanoparticles. Method. Carbon dots were synthesized using a one-step solvothermal method, and their composition and optical properties were analyzed using spectroscopy methods. Magnetic resonance imaging was conducted using a clinical magnetic resonance imaging scanner with a field strength of 1.5 T. Main results. In this study, two types of carbon dots were synthesized from o-phenylenediamine and gadolinium chloride or nitrate hexahydrate using the solvothermal method. Metal doping, at a concentration sufficient for further investigations, is achieved only when gadolinium chloride is used. Additionally, the presence of gadolinium chloride during the synthesis leads to the formation of luminescent centers within the carbon dots with emission at 600–720 nm and a photoluminescence quantum yield of 6.3%. In contrast, gadolinium nitrate increases the nitrogen content within the o-phenylenediamine-based carbon dots while inhibiting metal doping. The luminescent band with an emission maximum at 550 nm and a photoluminescence quantum yield of 7.4% originates from the o-phenylenediamine derivatives formed within such carbon dots. The study results also show that the gadolinium-doped carbon dots alter the relaxation times during magnetic resonance scanning, and the calculated relaxivity ( r 1 and r 2 ) values are 6.4 and 38.6L⋅mmol −1 ⋅s −1 , respectively. Thus, the synthesized carbon dots function as positive contrast agents during magnetic resonance scanning. Practical significance. Carbon dots with long-wavelength emission are promising nanoprobes for luminescence imaging. With gadolinium doping, these nanoparticles can also be used as contrast agents during magnetic resonance imaging. Consequently, carbon dots based on o-phenylenediamine and gadolinium chloride hexahydrate can be further utilized as dual-mode nanoprobes for bioimaging.