Hydroxyl rich graphene quantum dots for the determination of Hg(II) in the presence of large concentration of major interferents and in living cells

Abstract

Sensitive determination of Hg(II) by photoluminescence (PL) quenching of graphene quantum dots (GQDs) has been investigated extensively in the past. However, its selective determination was reported only in the presence of same concentration of other interferences. The present study reports the sensitive and selective determination of Hg(II) at pH 7 in the presence of 500- and 1000-fold higher concentration of Fe(III) and other metal ions, respectively using hydroxyl rich GQDs for the first time. The GQDs prepared from citric acid exhibit a strong blue luminescence with excitation independent emission properties. The PL of GQDs was completely vanished after the addition of Hg(II) whereas it was noticeably affected while adding Fe(III). However, the PL remains unaltered while adding other heavy and transition metal ions. Thus, the present fluorescent probe was used for the selective and sensitive determination of Hg(II). As the concentration of Hg(II) increases from 0 to 20 µM, the emission intensity linearly decreases with the correlation coefficient of 0.995 and the limit of detection (LOD) was found to be 9.87 nM (S/N=3). Among the different metal ions, Fe(III) alone interferes on the determination of Hg(II). However, the GQDs successfully determine Hg(II) in the presence of 500- and 1000-fold higher concentration of Fe(III) and other metal ions, respectively. The results obtained from the different spectroscopic and microscopic studies indicated that the quenching of GQDs was due to both complexation and formation of metallic Hg. The SEM studies showed that Hg(0) was formed on GQDs surface with size 10-20 nm. Finally, the present fluorescent probe was used to determine Hg(II) in different water samples and lung cancer cells.