Improving Pb2+ detection using DNAzyme-based fluorescence sensors by pairing fluorescence donors with gold nanoparticles

For previously reported fluorescence Pb2+ sensors, DNAzymes have lead to a significant increase in Pb2+ detecting sensitivity and specificity. However, these sensors suffer from incomplete fluorescence quenching and require additional steps for annealing DNAzymes and substrates as well as for removing the uncoupled substrates. In this study, we successfully overcome these issues by immobilizing the substrate nucleic acids on gold nanoparticles through thiol linkages. The immobilization of the substrate molecules to the gold nanoparticles lead to almost-complete fluorescence quenching and fast Pb2+ detection, without altering the Pb2+ specificity of the DNAzymes. After optimizing the concentration of DNAzymes, reaction time and pH, we could detect Pb2+ as low as 5 nM within 20 min without the preliminary and the post treatments. Considering the multi-color-fluorescence quenching capability of gold nanoparticles and the to-be-developed functional nucleic acids for other metal ions, this study could extend the application of DNAzymes to the detection of multiple heavy metal ions.