A colorimetric assay for Hg(II) based on the use of a magnetic aptamer and a hybridization chain reaction

We describe a colorimetric assay for mercury(II) ion. It is based on a hybridization chain reaction (HCR) and the use of Fe3O4@Au nanoparticles (NPs). Aptamers specific for Hg(II) were immobilized on the surface of the Fe3O4@AuNPs. The presence of Hg(II) inhibits the HCR process and this enables less Methylene Blue (MB) to intercalate into the dsDNA structure. After magnetic separation of the DNA-loaded NPs carrying Hg(II), the change in the absorbance of the residual MB solution is measured at 663 nm. The respective calibration plot is linear in the 1 to 300 nM concentration range, with a 0.7 nM detection limit (at a signal-to-noise ratio of 3). The method displays excellent selectivity over other metal ions. It was applied to the analysis of Hg(II) in spiked river water.