An electrochemical biosensor for the detection of Pb.sup.2+ based on G-quadruplex DNA and gold nanoparticles

We present a novel simple strategy for the detection of Pb.sup.2+ based on G-quadruplex DNA and gold nanoparticles. First, gold nanoparticles were chemically adsorbed onto the surface of a thiol-modified gold electrode. Subsequently, the substrate DNA1 was adsorbed onto the surfaces of the gold nanoparticles via thiol-gold bonds, so that the complementary guanine-rich DNA2 could be hybridized to the gold electrode in sequence. [Ru(NH.sub.3).sub.6].sup.3+ (RuHex), which can be electrostatically adsorbed onto the anionic phosphate of DNA, served as an electrochemical probe. The presence of Pb.sup.2+ can induce DNA2 to form a stable G-quadruplex and fall off the gold electrode. The amount of RuHex remaining on the electrode surface was determined by electrochemical chronocoulometry (CC). The prepared biosensor showed high sensitivity for Pb.sup.2+ with a linear range with respect to ln(c.sub.Pb2+) from 0.01 to 200 nM and a low detection limit of 0.0042 nM under optimal conditions. Because of the high selectivity of the Pb.sup.2+-specific DNA2, the designed biosensor also showed low false-positive signal rates with other metal ions in real-world examples. Therefore, this strategy has the potential for practical application in environmental monitoring.