A ratiometric fluorescent nanosensor for the detection of silver ions using graphene quantum dots

A ratiometric fluorescent nanosensor was reported for the first time for the sensitive and selective analysis of Ag+ ions by employing graphene quantum dots (GQDs) as the reference fluorophore and o-phenylenediamine (OPD) as the specific recognition probe. Upon the addition of Ag+ ions, OPD could be oxidized to produce 2,3-diaminophenazine (DAP) with a strong fluorescence emission at 557 nm, whereas the fluorescence of GQDs at 445 nm would be simultaneously quenched by the so generated DAP through fluorescence resonance energy transfer (FRET). A ratiometric fluorescent Ag+ nanosensor was thus developed. The fluorescence intensity ratios of DAP to GQDs linearly increased with the increasing of Ag+ concentrations in the range of 0–115.2 μM, with a detection limit down to 250 nM. Furthermore, the feasibility of practical applications of the developed detection strategy for probing Ag+ ions in real water samples was demonstrated.