DNAzyme-based sensing probe protected by DNA tetrahedron from nuclease degradation for the detection of lead ions.

Lead poisoning endangers soil, plants and human health due to its toxic effect. It is urgent to develop ideal tool for the in vivo detection of Pb2+.In this study, tetrahedron-based Pb2+-sensitive DNAzyme sensor (TPS) is constructed by taking advantages of a classic Pb2+-dependent GR-5 DNAzyme and DNA tetrahedral structure, where the cleavage substrate and DNAzyme are modified with fluorophore FAM and quencher BHQ-1, respectively. DNA tetrahedron is arranged at the terminus of substrate/DNAzyme duplex to offer the protective shield against the nuclease attack. In the absence of Pb2+, FAM and BHQ-1 are kept close and FAM fluorescence is efficiently quenched. However, in the presence of Pb2+ cofactor, the DNAzyme exhibits the catalytic activity and cleaves the substrate strands, spatially separating the FAM away from BHQ-1 and releasing fluorescence. Utilizing the sensing probe, the Pb2+ can be quantitatively detected down to 1 nM without the interference from nontarget metal ions. Even if incubating in the human serum solution for 12 h, no substantial nuclease degradation is detected. In different complex biological milieu, the TPS can preserve the 85% of fluorescence signal, indicating that the developed TPS is a promising tool for the future application in the in vivo detection of Pb2+.