A facile, simple and low-cost approach for synthesizing highly fluorescent carbon quantum dots (CQDs) from thermal treatment of sustainable hair has been developed. The resultant CQDs exhibited strong blue emission with a quantum yield of 10.75%, excellent photostability and high stability in high salt conditions. As the fluorescence of CQDs can be efficiently quenched by Hg2+, the CQDs can be constructed as a nanosensor for Hg2+ with good sensitivity and selectivity. And as low as 10 nM Hg2+ can be successfully detected.

Fluorescent copper nanoparticles (F-CuNPs) have received great attention due to their attractive features, such as water solubility, wide availability, ease of functionalization and good biocompatibility, and considerable efforts have been devoted to the preparation and applications of F-CuNPs. This review article comprises three main parts. In the first part, we briefly present the fluorescence properties of F-CuNPs. Then we cover the fabrication strategies of various F-CuNPs functionalized by different ligands. In the third part, we focus on the applications of F-CuNPs for sensing metal ions, including Hg(2+), Pb(2+), Cu(2+), Fe(3+) and other metal ions. Lastly, we further discuss the opportunities and challenges of F-CuNPs in the synthetic strategies and applications for sensing metal ions.

Nitrogen and boron doped carbon quantum dots (NB-CQDs) with yellow-green emission were prepared via hydrothermal method using 2-hydroxyphenylboronic acid and ethylenediamine in aqueous solution.The as-prepared NB-CQDs exhibited bright yellow-green emission, excellent stability in aqueous solution with high ionic strength and good biocompatibility. We further explored the applications of NBCQDs for sensing metal ions in aqueous solution. We found that the NB-CQDs could be utilized to sense Cr 2 O 7 2À in aqueous solution due to the Cr 2 O 7 2À-induced fluorescence quenching. In the sensing system, as low as 0.5 mM Cr 2 O 7 2À can be successfully detected and a good linear relationship in the range of 0-250 mM has been obtained. And the NB-CQDs can be also used as ink for writing on paper, revealing the NB-CQDs can be applied for anti-counterfeiting. Moreover, the NB-CQDs exhibit negligible cytotoxicity and good biocompatibility, which is favorable for bioimaging applications. And the NB-CQDs were successfully applied for fluorescence imaging in HeLa cells.