Fluorescent aptamer-functionalized graphene oxide biosensor for label-free detection of mercury(II).

Label-free fluorescent detection of Hg(2+) has been realized via quenching of fluorescence of graphene oxide (GO). The water-soluble GO sheets, which are functionalized with single-stranded DNA aptamer, exhibit strong fluorescence emission at 600 nm under the excitation of 488 nm in the absence of Hg(2+) ions. When Hg(2+) ions appear in the aqueous solution, Hg(2+) ions are sandwiched between the hairpin-shaped double-stranded DNA due to the formation of the thymine-Hg(2+)-thymine complex, which holds the Hg(2+) ions in proximity to the surface of GO sheets. As a result, the fluorescence emission of GO is quenched. The present GO-based sensor shows a limit of detection as low as 0.92 nM and excellent selectivity toward Hg(2+) over a wide range of metal ions. The present work indicates that GO is a promising fluorescent probe for detection of metal ions and biomolecules.