Morphological analysis of chromium in carbon quantum dots pairs Co-doped with zirconium and nitrogen and their applications in imaging of living cells.

As a new nanomaterial in the biochemistry field, carbon quantum dots (CDs) have been widely applied by scientists. In this study, CDs co-doped with zirconium and nitrogen (Zr-N-CDs) were synthesized quickly with lemon, ethylenediamine, and zirconium chloride through a hydrothermal method. The yield of Zr-N-CDs reached as high as 82.7%. The Zr-N-CDs showed outstanding water solubility in aqueous solution. The formation of Zr-N-CDs was verified by characterization technologies, such as high-resolution transmission electron microscopy (HRTEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Moreover, the optical properties of Zr-N-CDs were investigated through fluorophotometer and ultraviolet spectroscopy. The synthesized Zr-N-CDs were applied to test hexavalent chromium (Cr (VI)), which showed a good linear relationship with the fluorescence quenching of Zr-N-CDs. The limit of detection was 0.52 µM. An analytical method for Cr morphology in natural water areas was developed in this experiment. The sensor showed good stability. The results demonstrate that the sensor detected 98.35%-100.9% Cr (VI) recovery rate in water samples. Based on the cytotoxicity of Zr-N-CDs to human cervical cancer cells (HeLa cells), the Zr-N-CDs had no evident cytotoxicity. The applications of Zr-N-CDs in bioimaging of cells were determined through laser scanning confocal microscopy.