Label-free selective impedimetric detection of Cu2+ ions using catalytic DNA

Copper is an essential element for regulation of many biological processes, however, in excess it is considered to be toxic for human health. This metal is frequently accompanied by other elements such as cadmium, nickel and lead. Thus, developing a selective and simple method for determination of copper in a matrix containing other heavy metal ions is of great importance. In this work, a novel selective method for copper detection was developed using electrodes modified with the DNAzyme capturing Cu(2+) ions. The DNAzyme reconstituted with copper catalyzes oxidation of ascorbic acid leading to the build-up and adsorption of oxidation products on the electrode surface and produces changes in the interfacial properties of the electrode. The increase in the interfacial electron-transfer resistance is probed with electrochemical impedance spectroscopy (EIS) in the presence of the reversible redox couple [Fe(CN)6](3-)/[Fe(CN)6](4-) as a marker. The DNAzyme based biosensor combines excellent selectivity against other heavy metal ions with sufficient sensitivity to Cu(2+) in the range of 6.5-40 μM.