Thymine-Functionalized Gold Nanoparticles (Au NPs) for a Highly Sensitive Fiber-Optic Surface Plasmon Resonance Mercury Ion Nanosensor

Mercury ion (Hg(2+)) is considered to be one of the most toxic heavy metal ions. Once the content of Hg(2+) exceeds the quality standard in drinking water, the living environment and health of human beings will be threatened and destroyed. Therefore, the establishment of simple and efficient methods for Hg(2+) ion detection has important practical significance. In this paper, we present a highly sensitive and selective fiber-optic surface plasmon resonance (SPR) Hg(2+) ion chemical nanosensor by designing thymine (T)-modified gold nanoparticles (Au NPs/T) as the signal amplification tags. Thymine-1-acetic acid (T-COOH) was covalently coupled to the surface of 2-aminoethanethiol (AET)-modified Au NPs and Au film by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride/N-Hydroxysuccinimide (EDC/NHS) activation effect, respectively. In the presence of Hg(2+) ions, the immobilized thymine combines specifically with Hg(2+) ions, and forms an Au/thymine-Hg(2+)-thymine/Au (Au/T-Hg(2+)-T/Au) complex structure, leading to a shift in SPR wavelength due to the strong electromagnetic couple between Au NPs and Au film. Under optimal conditions, the proposed sensor was found to be highly sensitive to Hg(2+) in the range of 80 nM–20 µM and the limit of detection (LOD) for Hg(2+) was as low as 9.98 nM. This fiber-optic SPR sensor afforded excellent selectivity for Hg(2+) ions against other heavy metal ions such as Fe(3+), Cu(2+), Ni(2+), Ba(2+), K(+), Na(+), Pb(2+), Co(2+), and Zn(2+). In addition, the proposed sensor was successfully applied to Hg(2+) assay in real environmental samples with excellent recovery. Accordingly, considering its simple advantages, this novel strategy provides a potential platform for on-site determination of Hg(2+) ions by SPR sensor.