A "turn-off" fluorescent biosensor for the detection of mercury (II) based on graphite carbon nitride.

A novel and simple fluorescent biosensor has been realized through the fluorescence quenching of graphite carbon nitride (g-C3N4) for mercuric ion (Hg2+) detection. In this assay, the g-C3N4 sheets which were functionalized with single-stranded DNA (ssDNA) aptamer showed strong fluorescence emission at 440nm under the excitation of 380nm in the absence of Hg2+. When added to the assay solution, Hg2+ was embedded in the hairpin-shaped double-stranded DNA (dsDNA) due to the formation of the thymine-Hg2+-thymine (T-Hg2+-T) complex, which made the Hg2+ close to the surface of g-C3N4 sheet. Therefore, the fluorescence of g-C3N4 was quenched. This sensor has good selectivity with a limit of detection as low as 0.17nM under optimal conditions. The present work demonstrates that the g-C3N4-based fluorescent sensor has a promising application for detection of metal ions in real samples.