Abstract

Molecular imaging techniques such as fluorescence and magnetic resonance imaging play a significant role in monitoring human health but individually, they possess limitations. To address their shortcomings, contrast agents are used to improve the quality of the images; however, concerns usually arise due to their toxicity. Carbon dots offer an interesting alternative to be developed as multimodal probes and offer contrast enhancement in imaging techniques owing to their versatile optical properties, simple preparation, and biocompatibility. Herein, the synthesis of dual-fluorescent carbon dots functionalized with Mn2+ is presented. The dots were prepared using L-glutathione and formamide in a microwave reactor resulting in concomitant blue and red optical signatures following excitation at 420 nm. Surface decoration with paramagnetic Mn2+ was investigated via two parallel approaches namely direct electrostatic interactions and through chelation with diethylenetriaminepentaacetic acid with subsequent coordination of the metal cation. We investigated the physicochemical and optical properties with focus on preserving the red fluorescence for optical imaging, while maximizing metal cation loading for the magnetic resonance imaging modality. In vitro magnetic resonance imaging studies allowed for the identification of a lead candidate that offers good performance with an evident enhancement of the contrast of images when compared to clinically available contrast agents. Furthermore, toxicity assays demonstrated the low cytotoxicity of the dots, as well as the ones modified with metal cations suggesting good biocompatibility of this probe. Our results suggest that these Mn2+-doped carbon dots offer a strong potential as dual-modal contrast agents in fluorescence and magnetic resonance imaging applications.