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) (Pb2+) is described that is based on signal amplification by using an ion-dependent split DNAzyme and template-free DNA extension reaction. The Pb2+-dependent split DNAzyme was assembled on gold nanoparticles (Au@Fe3O4), and this nanoprobe then was exposed to Pb2+ which causes the split-off of DNAzymes to release primers containing 3′-OH groups (S1 and S2). 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 Pb2+. The use of a Pb2+-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 Pb2+.