Novel ratiometric surface-enhanced raman spectroscopy aptasensor for sensitive and reproducible sensing of Hg2+

It is important to precisely monitor mercury (II) ions (He) for environment protection and human health monitoring. Although many strategies have been developed in the past decades, there still remains a challenge for developing an ultrasensitive, simple and reliable approach to detect Hg2+. Herein, we report a ratiometric surface-enhanced Raman scattering (SERS) aptasensor by employing aptamer-modified Au@Ag core-shell nanoparticles (Au@Ag NPs) as highly functional sensing probes, allowing for ultrasensitive detection of Hg2+. In principle, the thiolated 5 '-Cy3 labeled aptamer probe (Cy3-aptamer) is firstly immobilized on the SERS substrate surface and then hybridizes with the 5 '-Rox labeled complementary DNA (cDNA) to form a rigid double-stranded DNA (dsDNA), in which the Cy3 and Rox Raman labels are used to produce the ratiometric Raman signals. In the presence of Hg2+, the aptamer DNA turns into the thymine (T)-Hg2+-T mediated hairpin structure, leading to the dissociation of dsDNA. As a result, the Rox labels are away from the Au@Ag NP SERS substrate while Cy3 labels are close to it. Therefore, the intensity of SERS signal from Cy3 labels increases while that from Rox labels decreases. The ratio between the Raman intensities of Cy3 labels and Rox labels is linear with Hg2+ concentrations in the range from 0.001 to 1.0 nM, and the limit of detection is estimated to be 0.4 pM. The proposed strategy provides a new rapid, simple and reliable approach for sensitive detection of Hg2+ and may create a universal methodology for developing analogous aptasensors for a wide range of other analytes determination.