We successfully developed a fluorometric paper-based
test kit for
the selective and sensitive determination of cyanide using nitrogen-doped
graphene quantum dots (N-GQDs) as the fluorescent probe. Citric acid
and tris(hydroxymethyl)aminomethane were precursors for the one-step
synthesis of N-GQDs via in situ hydrothermal methods,
providing a high quantum yield of 57.9%. The proposed mechanism uses
a fluorescence turn-on approach. Specifically, the fluorescence of
N-GQDs is quenched by the incorporation of Ag+ via a photoinduced
electron transfer (PET). During the detection step, sulfuric acid
converts cyanide (CN–) into hydrogen cyanide (HCN).
The Ag+ species on the N-GQD surface then react with the
evolved HCN via a coordination bond to form a silver cyanide complex,
resulting in the fluorescence emission of the N-GQDs being turned
back on. As a result, the fluorescence emission intensity of N-GQDs
linearly increased with increasing CN– concentrations
in the range of 0.5–25 mg L–1, with a limit
of detection (LOD) of 0.08 mg L–1. Notably, the
developed sensor has advantages in terms of simplicity, rapidity,
low cost, and high selectivity toward CN–. The analytical
performance of the test kit was also validated the performance of
the test kit against a conventional precipitation titration method.
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