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[Display omitted] • The N-CQDs were synthesized by a simple and economical one-pot hydrothermal method. • The prepared N-CQDs possess an ultra-high quantum yield (92.1%). • N-CQDs shows promising applications in sensing, bioimaging and anti-counterfeiting. The exploration of carbon quantum dots (CQDs) with ultra-high quantum yield, simple synthesis path, and satisfying output to facilitate their wide applications in numerous fields are always the research focus. In this work, nitrogen-doped carbon quantum dots (N-CQDs) with strong blue fluorescence were synthesized with a simple one-step hydrothermal method using citric acid and o-phenylenediamine as raw materials, and the absolute quantum yield was as high as 92.1%. The detailed research results demonstrate that the N-CQDs have outstanding fluorescence stability, high selectivity, and anti-interference in Hg2+ detection. The obtained N-CQDs also possess excellent biocompatibility, which can also be successfully applied in cell imaging and intracellular Hg2+ detection. Most importantly, due to their high quantum yield and excellent dispersibility, the N-CQDs solution can be used as a quick-drying fluorescent ink for ink-jet printing. Therefore, the as-prepared N-CQDs have great potential in fluorescence sensing, biomedical diagnosis, data encryption, and anti-counterfeiting. [ABSTRACT FROM AUTHOR]

The carbon quantum dot (CQD), a fluorescent carbon nanoparticle, has attracted considerable interest due to its photoluminescent property and promising applications in cell imaging and bioimaging. In this work, biocompatible, photostable, and sustainably sourced CQDs were synthesized from byproducts derived from a biorefinery process using one-pot hydrothermal treatment. The main components of byproducts were the degradation products (autohydrolyzate) of biomass pretreated by autohydrolysis. The as-synthesized CQDs had a size distribution from 2.0–6.0 nm and had high percentage of sp2 and sp3 carbon groups. The CQDs showed blue-green fluorescence with a quantum yield of ~13%, and the fluorescence behaviors were found to be stable with strong resistance to photobleaching and temperature change. In addition, it is found that the as-synthesized CQDs could be used for imaging of cells and tumors, which show potential applications in bioimaging and related fields such as phototherapy and imaging. [ABSTRACT FROM AUTHOR]