Surface-passivated, soluble and non-toxic graphene nano-sheets for the selective sensing of toxic Cr(vi) and Hg(ii) metal ions and as a blue fluorescent ink

Non-toxic amine-functionalized soluble graphene nano-sheets (f-GNS) were synthesized by using an old and well-known simple organic procedure. The f-GNS exhibited enhanced optical properties, such as strong blue fluorescence emission with a high value of quantum yield (∼13%). The O,O′-bis-(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol 800 as block polymeric amine (BPA)-passivized surface of f-GNS exhibited high aqueous solubility and excitation-dependent fluorescence emission behavior with a strong photo-stability performance. These f-GNS were tested for the significant selective sensing of toxic metal ions Cr(vi) and Hg(ii) from various tested toxic metal ions. The sensing experiment was supported by cyclic voltammetry analysis. The dual metal ion sensing method based on fluorescence showed the limit of detection (LOD) of ∼56 nM for Cr(vi) and ∼45 nM for Hg(ii) through a fluorescence quenching process. f-GNS were found to be non-toxic when tested over Escherichia coli (E.coli) cells. Additionally, the strong blue emission properties of f-GNS enabled their use as a suitable blue fluorescent ink under UV light illumination.