Au NPs-enhanced surface plasmon resonance for sensitive detection of mercury(II) ions

We reported a sensitive surface plasmon resonance (SPR) sensor for the detection of Hg2+ in aqueous solution by using a thymine (T)-rich, mercury-specific oligonucleotide (MSO) probe and gold nanoparticles (Au NPs)-based signal amplification. The MSO probe was first immobilized on gold film through formation of Au–S bond between DNA and gold film. In the presence of Hg2+, the MSO probe captured free Hg2+ in aqueous media via the Hg2+-mediated coordination of T–Hg2+–T base pairs. This direct immobilization strategy led to a detection limit of 0.3 μM of Hg2+. In order to improve the sensitivity, part complementary DNA (PCS)-modified Au NPs labels were employed to amplify SPR signals. We demonstrated that this Au NPs-based sensing strategy resulted in a detection limit down to 5 nM of Hg2+, brings about an amplification factor of two orders of magnitude. This Au NPs-based Hg2+ sensor also exhibited excellent selectivity over a spectrum of interference metal ions. Taking advantage of the high amplifying characteristic of Au NPs and the specificity of MSO to Hg2+ recognition, we developed here a SPR sensor for specific Hg2+ detection with high sensitivity.