Gadolinium-doped fluorescent carbon quantum dots as MRI contrast agents and fluorescent probes

In this research passivated gadolinium-doped carbon quantum dots (Gd-doped CQDs) were synthesized from starch by a hydrothermal method. The X-ray diffraction (XRD) pattern of the Gd-doped CQDs showed the formation of highly amorphous carbon. The Fourier transform infrared spectroscopy (FTIR) results suggested that the CQDs are functionalized with C-N and N–H bonds. The synthesized CQDs with a size distribution of 2–8 nm have an absorption peak at 271 nm in UV–Visible spectroscopy (UV–Vis). The photoluminescence (PL) in CQDs was dependent on the excitation wavelength. The QY of the synthesized CQDs was calculated to be 13.2%. The Gd-doped CQDs exhibited sustained PL in ionic solutions with different ionic strengths and different temperatures up to 65 °C. Fluorescence imaging on mouse C(34)/connective tissue-L929 cells confirmed that Gd-doped CQDs could be well distributed over the cytoplasm. The magnetic resonance imaging (MRI) showed that the Gd-doped CQDs have extremely high longitudinal and transverse relaxivity values of as high as 218.28 mM(−1) s(−1) and 364.68 mM(−1) s(−1). The synthesized Gd-doped CQDs are promising candidates as multifunctional imaging probes and MRI contrast agents in biomedical diagnosis and brain mapping applications.