Magnetofluorescent Carbon Dots Derived from Crab Shell for Targeted Dual-Modality Bioimaging and Drug Delivery

We propose a one-pot microwave-assisted pyrolysis method for fabrication of magnetofluorescent carbon quantum dots (MFCQDs), using a combination of waste crab shell and three different transition-metal ions, Gd3+, Mn2+, and Eu3+, referred to as Gd@CQDs, Mn@CQDs, and Eu@CQDs, respectively. Chitin from waste crab shell acted not only as a carbon source but also as a chelating ligand to form complexes with transition-metal ions. Gd@CQDs exhibited a high r1 relaxivity of 4.78 mM–1·s–1 and a low r2/r1 ratio of 1.33, suggesting that they show excellent potential as a T1 contrast agent. Mn@CQDs and Eu@CQDs showed high r2 relaxivity values of 140.7 and 28.32 mM–1·s–1, respectively, suggesting their potential for use as T2 contrast agents. Further conjugation of Gd@CQDs with folic acid (FA) enabled specific targeting to folate receptor-positive HeLa cells, as confirmed via in vitro magnetic resonance and fluorescence imaging. Doxorubicin (DOX) was selected as a model drug for conjugation with FA-Gd@CQDs. The as-prepared nanocomposites showed significantly higher cytotoxicity toward HeLa cells than free DOX. No apparent cytotoxicity was observed in vivo (zebrafish embryos) or in vitro (cell viability), suggesting that MFCQDs show potential for development as diagnostic probes or theranostic agents.