Electrochemical lead(II) biosensor by using an ion-dependent split DNAzyme and a template-free DNA extension reaction for signal amplification

A voltammetric biosensor for lead(II) (Pb 2+ ) is described that is based on signal amplification by using an ion-dependent split DNAzyme and template-free DNA extension reaction. The Pb 2+ -dependent split DNAzyme was assembled on gold nanoparticles (Au@Fe 3 O 4 ), and this nanoprobe then was exposed to Pb 2+ which causes the split-off of DNAzymes to release primers containing 3′-OH groups (S 1 and S 2 ). The template-free DNA extension reaction triggers the generation of long ssDNA nanotails, which then can bind the free redox probe N,N′-bis(2-(trimethylammonium iodide)propylene)perylene-3,4,9,10-tetracarboxyldiimide (PDA + ) via electrostatic adsorption. Hence, the concentration of PDA + in solution is reduced. Therefore, less free PDA + can be immobilized on a glassy carbon electrode modified with electrodeposited gold nanoparticles (depAu) to produce an electrochemical signal, typically measured at ∼0.38 V ( vs . SCE) for quantitation of Pb 2+ . The use of a Pb 2+ -dependent split DNAzyme avoids the usage of a proteinic enzyme. It also increases the sensitivity of the sensor which has a lower detection limit of 30 pM of Pb 2+ . Graphical abstract Novel electrochemical biosensor based on the amplification of ion-dependent split DNAzyme and template-free DNA extension reaction for trace detection of Pb 2+ .