A novel strategy based on DNAzyme for electrochemiluminescence detection of Pb(II) with P-GO@QDs for signal amplification

A novel, simple, and versatile electrochemiluminescence (ECL) sensing platform for Pb(II) ions was developed based on DNAzyme with peroxidase-like activity to catalyze the reduction of hydrogen peroxide. Poly (diallyldimethylammonium chloride) (PDDA) with positive charge was adsorbed onto the surface of graphene oxide (GO) and then CdS quantum dots (QDs) with negative charge were enriched to the surface of GO by electrostatic interaction between CdS QDs and PDDA to prepare a composite (denoted as P-GO@QDs) which was immobilized on the surface of a glassy carbon electrode (GCE). When hydrogen peroxide was used as coreactant CdS QDs can produce ECL signal. G-rich DNA strand, i.e. T30695, can combine with Pb (II) ions to form a stable parallel Gquadruplex. The G-quadruplex can further combine with hemin to form DNAzyme which have catalysis towards the reduction of hydrogen peroxide causing the decrease of ECL signal. Amino-modified T30695 was attached to P-GO@QDs composite by the reaction between the amino group of T30695 and carboxyl group of CdS QDs. The ECL signal of the biosensor was linearly dependent on the logarithm of Pb(II) concentration from 1.0 x 10(-14) to 1.0 x 10(-11) M with a detection limit of 9 fM. An excellent performance of ECL biosensor indicated that it is promising for Pb(II) detection in real samples.