DNA Modified Fe3O4@Au Magnetic Nanoparticles as Selective Probes for Simultaneous Detection of Heavy Metal Ions.

Driven by the urgent need to detect trace heavy metal ions in various real water samples, this article demonstrates for the first time an electrochemical biosensor based on DNA modified Fe3O4@Au magnetic nanoparticles (NPs). Three DNA probes are designed to contain certain mismatched base pairs. One is thiolated and modified on the surface of Fe3O4@Au NPs (DNA 1). The other two probes (DNA 2 and 3) are labeled with two independent electrochemical species. Stable structures of cytosine-Ag+-cytosine and thymine-Hg2+-thymine formed in the presence of Ag+ and Hg2+ can assist the hybridization of DNA 1/DNA 2 and DNA 1/DNA 3, which locate corresponding electrochemical species onto the surface of the magnetic NPs. The achieved nanocomposites are then used as selective electrochemical probes for the detection of heavy metal ions by recording the square wave voltammetry signals. Simultaneous detection of Ag+ and Hg2+ is demonstrated without significant interference, and their individual high sensitivities are fundamentally preserved, which meet the requirements of U.S. Environmental Protection Agency (USEPA). Furthermore, the proposed method has been challenged by various real water samples. The results confirm the DNA modified magnetic NPs based sensing method may have potential applications for the monitoring of heavy metal ions in real sample analysis.