Bottom-up and green-synthesis route of amino functionalized graphene quantum dot as a novel biocompatible and label-free fluorescence probe for in vitro cellular imaging of human ACHN cell lines.

• His-GQDs synthesized via pyrolysis green-synthesis route. • His-GQDs were used for cellular imaging of ACHN cell lines as a novel bright green fluorescence probe. • This is the first reported of label-free, selective and non-toxic fluorescence probe for cellular imaging of ACHN cell lines. • Cellular imaging was achieved successfully show that His-GQDs can be easily penetrated into cytoplasm. In this study, bright green-luminescent probe (His-GQDs) were synthesized using a new one-pot "bottom-up" pyrolysis green-synthesis route, without consuming any water and chemical reagent. Citric acid as carbon source and Histidine as amino-functionalized agent, with optimized ratios, were used for fabricating His-GQDs as a novel, label-free, and selective probe. His-GQDs can be then used for cellular imaging of human ACHN cell lines that are composed of graphene sheets with the average size of 2.0 nm. Obtained His-GQDs probe has ultra-small size, low toxicity, chemical stability, biocompatibility, anti-photo bleaching and excellent optical properties with a rather high quantum yield of 62.8%. The detailed structural studies were confirmed by FT-IR, HR-TEM and powdered X-ray diffraction analysis respectively. In this project, the His-GQDs were utilized for cellular imaging of human ACHN cell lines for the first time. This probe indicated the presence desired biocompatibility of His-GQDs in human ACHN cell lines even at high their concentration (1800 µg mL−1) at 24 h post-treatment and their distribution in ACHN cell lines cytoplasm. [ABSTRACT FROM AUTHOR]