Biosensors: Label‐Free Colorimetric Detection of Nucleic Acids Based on Target‐Induced Shielding Against the Peroxidase‐Mimicking Activity of Magnetic Nanoparticles (Small 11/2011)

The cover image illustrates how target polymerase chain reaction (PCR) products shield the peroxidase mimicking activity of magnetic nanoparticles (MNPs), leading to a significantly reduced colorimetric signal as compared to the intense colorimetric response by the normal peroxidase activity of MNPs. In the case where PCR products are not formed because a target DNA is absent, MNPs display their normal peroxidase activity generating the red color. On the other hand, peroxidase activity is significantly reduced in the presence of target DNA because the resulting PCR products greatly diminish the accessibility of the colorimetric substrate, o-phenylenediamine. In addition, DNA directly adsorbs onto the surface of MNPs, leading to significant inhibition of the substrate binding to the MNPs, which is required for the peroxidaselike reaction. As a result, the colorimetric substrate is not converted to a red product, retaining its original yellow color. For more information, please read the Communication “Label-Free Colorimetric Detection of Nucleic Acids Based on Target-Induced Shielding Against the Peroxidase-Mimicking Activity of Magnetic Nanoparticles” by H. G. Park and co-workers, beginning on page 1521.