Colorimetric assay for mercury (II) based on mercury-specific deoxyribonucleic acid-functionalized gold nanoparticles

A colorimetric nanoprobe—mercury-specific DNA-functionalized gold nanoparticles (Au–MSD) was developed for sensing Hg2+. The new mercury-sensing concept relies on measuring changes in the inhibition of “non-crosslinking” aggregation of Au–MSD-induced by the folding of mercury-specific DNA strand through the thymine–Hg2+–thymine (T–Hg2+–T) coordination. In the absence of Hg2+, a high concentration of MgCl2 (50 mM) results in a rapid aggregation of Au–MSD because of the removal of charge repulsion. When Hg2+ is present, the particles remain stable due to the folding of MSD functionalized on the particle surface. The assay enables the colorimetric detection of Hg2+ in the concentration range of 0.1–10 μM Hg2+ ions with a detection limit of 60 nM, and allows for the selective discrimination of Hg2+ ions from the other competitive metal ions. Toward the goal for practical applications, the sensor was further evaluated by monitoring Hg2+ in fish tissue samples.