Fluorescent carbon dots derived from urine and their application for bio-imaging

This study aims to obtain water-soluble fluorescent carbon dots (C-dots) from low-value metabolites through a simple, economical, one-step synthetic route. The urine C-dots (UCDs) and hydrothermally treated urine C-dots (HUCDs) were obtained, respectively, using straightforward Sephadex filtration method from human adults and hydrothermal reaction method. The UCDs and HUCDs emit fluorescence upon being excited with ultraviolet light with a quantum yield of 4.8% and 17.8%, respectively. TEM analysis revealed that UCDs and HUCDs had an average size of 2.5 nm and 5.5 nm, respectively. X-ray photoelectron spectroscopy (XPS) analysis showed the UCDs and HUCDs were mainly composed of carbon, oxygen and nitrogen. Fourier-transform infrared (FTIR) spectroscopy demonstrated the presence of functional groups, such as amino, hydroxyl, carboxylate and carbonyl groups onto the C-dots. The UCDs and HUCDs can be directly used for in vivo and in vitro imaging in Hela cells, Caenorhabditis elegans, onion epidermal cells and bean sprouts. The cytotoxicity study revealed that the UCDs and HUCDs were not toxic to normal rat kidney (NKR) cells with good biocompatibility. The results revealed that the C-dots derived from urine have good biocompatibility, strong fluorescence and may have potential to be a safe fluorescent probe for bio-imaging.