A simple colorimetric assay for the detection of metal ions based on the peroxidase-like activity of magnetic nanoparticles

We developed a simple colorimetric assay for the detection of metal ions based on the peroxidase-like activity of magnetic nanoparticles (MNPs) and their interactioin with target specific single-stranded DNA (ssDNA). It was already known that MNPs easily oxidize substrates in the presence of hydrogen peroxide same as a peroxidase. In this study, the target specific ssDNA was adsorbed on the positively charged surface of MNP, then the catalytic activity of MNPs was reduced by the screening effect of adsorbed ssDNA on the surface of MNPs to substrates. The peroxidase like activity of MNPs was recovered by the addition of targets because the target specific ssDNA were displaced from MNPs by the interaction between targets and their specific ssDNA. The degree of color change of mixture was proportional to the concentration of mercury ion in a range of 5–75 μM. In control experiment, other metal ions did not induce the color change.