Near-infrared emissive lanthanide hybridized carbon quantum dots for bioimaging applications

Lanthanide hybridized carbon quantum dots (Ln-CQDs) were synthesized by a facile one-pot hydrothermal method using citric acid as a carbon precursor and Yb³⁺ or Nd³⁺ as a doping ion. The morphology and chemical structures of Ln-CQDs were investigated by TEM, XRD, XPS, and FTIR spectroscopy. The obtained Ln-CQDs are spherical and well dispersed in water, and their aqueous solutions emit strong blue emission under UV excitation. The Ln-CQDs exhibit excitation-dependent PL behavior with the emission maximum ranging from 443 to 552 nm under 300-520 nm excitation. Moreover, the carbon quantum dots can not only act as visible imaging agents, but also as antennae for photoluminescence (PL) of lanthanide ions. Hence, CQDs hybridized with Yb³⁺ or Nd³⁺ ions exhibit the characteristic emission in the near-infrared region with the emission maximum centered at about 998 and 1068 nm, respectively. The MTT assay against HeLa cells verified the low cytotoxicity of Ln-CQDs. They have been used as excellent optical probes for multicolor cell-imaging, demonstrating their great potential for both visible/NIR bioimaging and biomedical applications in vivo.