Red-fluorescent graphene quantum dots from guava leaf as a turn-off probe for sensing aqueous Hg(ii)

Therapeutic guava (Psidium guajava) leaf was used to green synthesize novel red-fluorescent graphene quantum dots (G-GQD) and their fluorescence quenching characteristic was exploited for the sensitive and selective detection of Hg(ii), a hazardous metal pollutant, in aqueous media. An eco-friendly and low-cost approach was demonstrated for the preparation of fluorescent G-GQD by the one-pot single-step solvothermal treatment of guava leaf extracts, emitting in the far-red spectral region of 620 to 780 nm with the maximum intensity near 673 nm. The as-fabricated G-GQD revealed excitation wavelength (300-420 nm)-dependent as well as pH (2-7.2)-dependent fluorescence intensity, but without any shift in emission peak wavelength. The emission property of the as-fabricated G-GQD was utilized as a fluorescence turn-off probe for the selective quantification of aqueous Hg2+, with a limit of detection of 82 mu M, over a large dynamic range of up to 0.38 mM. The effect of other co-existing metal salts, particularly the presence of paramagnetic ions, such as Cu2+, Co2+, Fe2+, and Al3+, which are known fluorescence quenchers, did not show any interference with Hg+2 selectivity by the fluorescent G-GQD. These results indicate the potential applicability of the convenient, eco-friendly and cost-effective G-GQD for its rapid, selective, and sensitive fluorescence sensing response toward Hg(ii) ion in polluted water bodies. Moreover, such a type of fabricated far-red emitting G-GQD not only overcomes the limitation of conventionally reported fluorescent GQD sensors emitting in the blue and green spectral regions, but also widens the horizon for different green-synthesized GQDs in metal and biochemical sensing applications also in the biologically advantageous red region of the visible spectrum.

Automated summary

Therapeutic guava leaf was used to green synthesize novel red-fluorescent graphene quantum dots (G-GQD) for sensitive and selective detection of Hg(ii) in aqueous media, showing a potential for rapid, selective, and sensitive fluorescence sensing response towards polluted water bodies.