Electrochemical determination of Pb2+based on DNAzyme-triggered rolling circle amplification and DNA-templated silver nanoclusters amplification strategy

Lead ion (Pb2+) is one of the most widespread heavy metal contaminants that pose detrimental impact on environment and human health. An electrochemical biosensor was developed for detection of Pb2+ based on rolling circle amplification (RCA) of Pb2+-dependent DNAzyme and DNA-templated silver nanoclusters (DNA-AgNCs) mediated amplification strategy. The Pb2+-dependent DNAzyme (catalytic strand) hybridized with substrate strand to form a duplex structure. In the presence of Pb2+, DNAzyme was activated and cleaved sub-strate strand into two fragments at the "rA" site, releasing the enzyme strand as a padlock probe for subsequent RCA. The padlock probe hybridized with primer strand to form a circular template, which triggered RCA reaction in the presence of phi29 DNA polymerase and dNTPs. The resulted RCA product hybridized with DNA-AgNCs, catalyzing H2O2 to generate enhanced electrochemical signal. The electrochemical signal was proportional to the concentration of Pb2+ in the range of 1 pM-10 mu M with a detection limit of 0.3 pM (S/N = 3). The proposed strategy exhibits highly sensitive and selective for Pb2+ analysis, providing potential application in real water samples and environment analysis.