A Pb2+-ion electrochemical biosensor based on single-stranded DNAzyme catalytic beacon

A novel strategy for selective and sensitive electrochemical lead ion (Pb 2+ ) biosensor was developed based on the single-stranded DNAzyme catalytic beacon. A DNAzyme that requires Pb 2+ for activation was selected and labeled with redox-active ferrocene (Fc) for signal transducer. The Fc-labeled single-stranded DNAzyme (Fc-ssDNAzyme) was self-assembled through S Au bonding on a gold electrode surface. In the presence of Pb 2+ , the ssDNAzyme was activated and catalyzed the hydrolytic cleavage of the substrate strand, resulting in the removal of the substrate strand along with the Fc from the Au electrode surface. The dissociation of Fc caused a decrease of electrochemical signal (“signal-off”). Under the optimal conditions, the electrochemical signal of Fc decreased directly with the increasing Pb 2+ concentration, exhibiting a linear response in the range of 0.5   nM to 5   μM with a detection limit of 0.25   nM. This strategy is simple, sensitive and selective with the minimal reagents and working steps, thereby holds great potential for Pb 2+ detection in real environmental sample analysis.