A Localized Surface Plasmon Resonance Light-Scattering Assay of Mercury (II) on the Basis of Hg2+-DNA Complex Induced Aggregation of Gold Nanoparticles

It is known that localized surface plasmon resonance (LSPR) is responsible for the surface-enhanced spectroscopic processes of metallic nanoparticles and thus LSPR spectroscopy has become a powerful technique for chemical and biological purposes. In this contribution, we present a simple homogeneous Hg2+ assay by measuring enhanced LSPR scattering signals resulted from Hg2+-DNA complex induced aggregation of gold nanoparticles (AuNPs). In a medium of pH 7.4 tris-HCl buffer containing 0.05 M NaCl, 'single-stranded oligonucletides with the sequence of 5'-d(T-6)-3' (poly-T-6 ssDNA), can be selectively adsorbed onto the surface of gold colloids, stabilizing the AuNPs against aggregation. If Hg2+-DNA complex via Hg2+- mediated thymine-Hg2+-thymine (T-Hg2+-T) is formed, however, the adsorption of poly-T-6 ssDNA onto the surface of gold colloids gets reduced, and then aggregation of the AuNPs occurs owing to the decrease of the electrostatic repulsion between AuNPs. Consequently, strong LSPR scattering signals resulting from the aggregates of AuNPs could be visually observed under a dark field microscope and easily be measured with a common spectrofluorometer. The LSPR scattering intensities characterized at 556.0 nm were found to be proportional to the concentration of Hg2+ ions in the range of 4.0 x 10(-8) to 6.0 x 10(-7) M with the limit of determination (3 sigma) of 1.0 nM. Compared with reported calorimetric methods, our present approaches display the advantages of higher sensitivity.