A fluorescent biosensor based on carbon dots-labeled oligodeoxyribonucleotide and graphene oxide for mercury (II) detection.

As the newest two members of the carbon materials family, carbon dots (CDs) and graphene oxide (GO) possess many excellent optical properties resulting in a wide range of applications. In this work, we successfully synthesized CDs with a high-quantum-yield, and labeled them on oligodeoxyribonucleotide (ODN). The fluorescence of resultant CDs-labeled oligodeoxyribonucleotide (ODN-CDs) was quenched by GO via fluorescence resonance energy transfer. In the presence of Hg(2+), the fluorescence was recovered by the release of ODN-CDs from GO due to the formation of T-Hg(2+)-T duplex. In the light of this theory, we designed a simple, highly sensitive and selective fluorometric Hg(2+) sensor based on CDs-labeled oligodeoxyribonucleotide and GO without complicated, costly and time-consuming operations. Under the optimal conditions, a linear relationship was obtained between relative fluorescence intensity and the concentration of Hg(2+) in the range of 5-200 nM (R(2)=0.974). The present GO-based sensor system is highly selective toward Hg(2+) over a wide range of metal ions and has a detection limit of 2.6 nM. This method is reliable, and has been successfully applied for the detection of Hg(2+) in practical samples.