A label-free SERS approach to quantitative and selective detection of mercury (II) based on DNA aptamer-modified SiO 2 @Au core/shell nanoparticles

Abstract A prototype of label-free SERS sensor, based on the formation of T-Hg 2+ -T pairs and the corresponding orientation variation of DNA on Au shell surface, was developed for detection of Hg 2+ in aqueous solution quantitatively and selectively. The DNA aptamer immobilized on the surface of SiO 2 @Au core/shell nanoparticles (NPs) consisted of two segments, namely, the segment which has the consecutive thymines (T) severing as the Hg 2+ recognition elements, and the segment which contains the guanine (G) and adenine (A) bases working as the signal reporter. With interaction of Hg 2+ ions and the thymines between the adjacent single-stranded DNA (ssDNA), the DNA molecule adopted vertical orientation, resulting in increase of Raman intensity ratio I(660 cm −1 )/I(736 cm −1 ) with increase of Hg 2+ concentration, which thus allowed to measure trace amounts of Hg 2+ in aqueous solution selectively and quantitatively. Our results revealed that this label-free SERS sensor could sensitively respond to Hg 2+ ions within a wide concentration range (from 1 × 10 −8 to 1 × 10 −3  M). This work therefore demonstrates that proper design of aptamer-modified SiO 2 @Au core/shell NPs can be utilized for label-free SERS detection of heavy metal ions in the environment.