Reusable DNA-functionalized-graphene for ultrasensitive mercury (II) detection and removal

Mercury is a bioaccumulative and highly toxic heavy metal. Thus, the removal and detection of Hg²⁺ from the environment is a major challenge. This paper reports a novel bio-nanomaterial for the simultaneous determination and removal of Hg²⁺ with the use of rGO-Fe₃O₄ functionalized with Hg²⁺-specific thymine oligonucleotide (T-DNA). T-DNA interacts with Hg²⁺ and changes from having a random coil into a hairpin structure, thereby increasing the fluorescence of SYBR Green I. Such fluorescence turn-on process allows the detection of Hg²⁺ in the concentration range of 1-20ng/mL, with a detection limit of 0.82ng/mL. Removal is achieved by exploiting the T-Hg²⁺-T base pairs and the large surface area of graphene; these bio-nanocomposites exhibit excellent removal efficiency (over 80%) and rapid separation from the aqueous solution. Moreover, bio-nanomaterials can be regenerated after a simple treatment. The proposed method also demonstrates the evident practicability of the simultaneous detection and removal of Hg²⁺ in lake water samples.