Highly Sensitive Fluorometric Hg2+ Biosensor with a Mercury(II)-Specific Oligonucleotide (MSO) Probe and Water-Soluble Graphene Oxide (WSGO)

A highly sensitive and selective, turn-on and simple Hg2+ biosensor is reported by using water-soluble graphene oxide (WSGO) and dye-labeled mercury(II)-specific oligonucleotide (MSO) probe. The probe is rich of thymine (T) and can readily form the stem-loop structure which consists of the T-Hg2+-T configuration. In the absence of Hg2+, the probe exists as a random coil conformation which can be readily adsorbed on the surface of WSGO by strong noncovalent binding of bases, as a result, the fluorescence of the dye labeled on the terminus of the MSO is strongly quenched by the efficient electron/energy transfer from the dye to WSGO. Upon addition of Hg2+, the formation of the T-Hg2+-T structure releases the MSO from the surface of WSGO, resulting in a restoration of the fluorescence of dye-labeled MSO probe. Based on this observation, a highly sensitive and selective Hg2+ sensor is developed, which can work with turn-on mode in aqueous solutions at room temperature. By using the fluorometric method, the limit of detection for Hg2+ can reach picomolar range (187 pmol.L-1), and it is demonstrated that the biosensor is highly selective and only minimally perturbed by a wide range of non-specific metal ions.