Heavy metal ion detection using a capacitive micromechanical biosensor array for environmental monitoring

Heavy metal ions are major contaminants in present day water supply. In this work the fabrication and evaluation of a DNAzyme functionalized capacitive micromechanical sensor array for the detection of lead ions is presented. The catalytic strand of a “8–17” DNAzyme can cleave a substrate DNA strand that has one ribonucleotide base, in the presence of Pb2+, dissociating the complex into three fragments. The DNAzyme strand is laser printed and immobilized on the sensor surface and hybridized with the substrate strand. When self-cleaving occurs, the surface stress changes, which is then registered as change in the capacitance of the device. The sensor was able to detect 10 μM of Pb2+, whilst in a reverse procedure the re-hybridization of the immobilized catalytic strand with the substrate strand was demonstrated. The reactions were validated by tagging the catalytic strand with FAM (6-carboxyfluorescein), while the substrate strand was tagged with Dabcyl, a quencher.