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 Hg ²⁺ 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.