Highly fluorescent graphene quantum dots as "turn off–on" nanosensor for detecting toxic metal ions to organic pollutant.

A high photoluminescence (PL)-based nanosensor based on graphene quantum dots (GQDs) is fabricated for the detection of toxic ions Ag⁺, Ce²⁺, Cd²⁺, Cu²⁺, Cr²⁺, Pb²⁺, Sn²⁺, and Fe³⁺, p-nitrophenol, and thioacetamide in water. The quenching of PL spectra indicates that the complex of GQDs/Fe(III) shows a high florescent quenching efficiency (~ 75%) toward the hydrophobic surface of the GQDs. The limit of detection for Fe(III) concentration 40 ± 2 nM, with high linearity and sensitivity. The change of the zeta potential value proves the attachment of Fe (III) ions to the surface of the GQDs. The GQDs/Fe(III) complexes can be utilized as a turn-OFF or turn-ON type fluorescence probe for p-nitrophenol (turn-OFF) detection with 5 ± 1 pM concentration and the sulfur (turn-ON) detection with 7.6 ± 1 pM. The proposed method is facile, sensitive and fast, which makes it ideal for nanosensors to detect water quality of rivers, ponds, or industrial wastes. [ABSTRACT FROM AUTHOR]