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.

Optimized channel allocation scheme for jointly reducing four-wave mixing and Raman scattering in the DWDM-QKD system.

Conducting quantum key distribution (QKD) through existing optical fibers together with conventional communication signals is a viable way to expand its practical application, but weak quantum signals can be severely disrupted by co-propagating classical signals. In this paper, the suppression of four-wave mixing (FWM) noise and Raman noise is considered simultaneously for the first time, to the best of our knowledge, and the joint optimized channel allocation (JOCA) scheme is proposed. In the JOCA scheme, the quantum channels and classical channels are interleaved with each other to avoid FWM noise and optimal quantum channel positions are chosen in variable conditions according to the Raman scattering spectrum. Experimental measurements of the noise photons show that the JOCA scheme can effectively reduce the impairments on quantum signals compared with the single-target schemes. Additionally, simulation results verify that the JOCA scheme can increase the secure key generation rate and transmission distance, and that it also enables the DWDM-QKD system to tolerate higher-power classical signals and more classical channels, which improve the compatibility with a high-capacity communication system.