Small　amount　of　lead　ions　(Pb2+)　can　cause　great　harm　to　human　health,　it　is　important　to　develop　some　simple　but　sensitive　methods　to　detect　Pb2+　quickly　and　accurately.　In　this　study,　a　sensitive　method　has　been　developed　for　Pb2+　detection　based　on　the　difference　of　gold　monomer　ratio　using　a　dark　field　microscope　(DFM)　as　readout　system.　The　proposed　method　employed　single-particle　gold　nanoparticles　(AuNPs)　and　8–17　DNAzyme　as　signal　converter　and　identification　unit,　respectively.　The　8–17　DNAzyme　consists　of　a　catalytic　strand　and　a　substrate　strand,　the　5′　end　of　the　two　strands　are　modified　with　sulfhydryl　groups.　The　8–17　DNAzyme　is　firmly　modified　on　the　surface　of　AuNPs　(50　nm,　AuNPs1)　in　advance,　in　the　absence　of　Pb2+,　AuNP　aggregation　is　occurred　by　adding　AuNPs　(20　nm,　AuNPs2)　as　they　can　interact　with　the　other　end　of　the　dsDNA.　In　the　presence　of　Pb2+,　due　to　the　specific　cleavage　of　the　substrate　chain　by　Pb2+,　another　–SH　leaves　away　from　AuNPs1,　the　aggregation　of　AuNPs　cannot　be　occurred.　AuNP　aggregates　can　be　easily　distinguished　from　the　monomers　under　DFM　because　the　aggregation　can　induce　green-to-yellow　scattering　color　changing,　and　the　monomer　ratio　summarized　by　Image　J　can　be　used　for　quantitative　analysis.　The　linear　response　range　is　0.1–100.0　pM　with　a　detection　limit　of　0.075　pM.　The　proposed　method　has　been　applied　to　detect　Pb2+　in　lake　water　and　human　blood　serum　samples　with　satisfied　results.　©　2021　Elsevier　B.V.