Manganese-doped carbon quantum dots for fluorometric and magnetic resonance (dual mode) bioimaging and biosensing

Manganese-doped carbon quantum dots (MnCQDs) were prepared through one-step hydrothermal method using citric acid and manganese tetraphenyl porphyrin as carbon sources in aqueous media. The structure of MnCQDs was confirmed by TEM, XRD, and XPS. The MnCQDs display a typical excitation-dependent emission behavior and exhibit bright green luminescence (with a peak at 482 nm) under UV irradiation (365 nm) and a fluorescence quantum yield of 13%. The MnCQDs can be used as a fluorescent probe for ferric ion in aqueous solution with a 220 nM detection limit. The MTT assay demonstrated the low cytotoxicity of MnCQDs towards HeLa cells. Due to the excitation-dependent emission properties, MnCQDs can be used as a multi-color (blue, green, and red) bioimaging agent in cancer cells and in living zebrafish. The application of MnCQDs as selective biosensing probe for Fe³⁺ was also realized in cells and zebrafish mode. Because of the existence of paramagnetic ions, MnCQDs demonstrate an enhanced magnetic resonance (MR) signal. Thus, the MnCQDs can serve as a positive contrast agent for MR imaging. Graphical abstract Schematic presentation of the preparation of luminescent manganese-doped carbon quantum dots (MnCQDs). MnCQDs showed good magnetic resonance effect and can be used as a fluorescence probe for the detection of Fe³⁺ in HeLa cells and zebrafish.