A label–free GR–5DNAzyme sensor for lead ions detection based on nanoporous gold and anionic intercalator

Abstract

A label–free electrochemical sensor, based on a classic lead ions (Pb2+)–dependent GR–5DNAzyme as the catalytic unit, disodium–anthraquinone–2,6–disulfonate (AQDS) as DNA intercalator, and nanoporous gold (NPG) for signal amplification, was designed for sensitive and selective detection of Pb2+. Firstly, NPG modified electrode surface were employed as a platform for the immobilization of thiolated probe DNA, and then, hybridized with DNAzyme catalytic beacons. The Pb2+–induced catalytic reaction makes the substrate strand break at the cleavage sitGe irreversibly, which disturbs the formation of DNA strands. AQDS served as an indicator that intercalated into the base–pairing regions of DNAzyme, resulting in a strong electrochemical signal. In the presence of Pb2+, the complementary regions were reduced, due to the fracture of the DNA strand, resulting in the release of AQDS. And a decreased current was obtained, corresponding to Pb2+ concentration. Taking advantage of the amplification effect of NPG electrode for increasing the reaction sites of thiol modified capture probe, the proposed electrochemical biosensor could detect Pb2+ quantitatively, in the range of 1–120nM, with a limit of detection as low as 0.02nM, which is much lower than the maximum contamination level for Pb2+ in drinking water defined by the U.S. Environmental Protection Agency. The electrochemical sensor was also used to detect Pb2+ from real water samples, and the results showed excellent agreement with the values determined by inductively coupled plasma mass spectroscopy. This biosensor showed a promising potential for on–site detecting Pb2+ in aqueous environment.