A　new　label-free　DNA　sensing　protocol　was　designed　for　fluorescent　detection　of　mercury(II)　(Hg2+),　coupling　hairpin　DNA-scaffolded　silver　nanocluster　(DNA-AgNC)　with　exonuclease　III-assisted　target　recycling　amplification.　The　assay　was　carried　out　through　target-induced　conformational　change　of　hairpin　DNA,　while　the　signal　derived　from　the　formed　silver　nanoclusters　on　hairpin　DNA　probes.　Initially,　target　Hg2+　was　specifically　coordinated　with　thymine-thymine　(T-T)　mismatches　to　form　an　intact　hairpin　DNA.　Then,　the　newly　formed　hairpin　DNA　was　digested　through　exonuclease　III　from　blunt　3＇　termini　and　restrained　at　3＇　protruding　terminus,　thus　resulting　in　the　release　of　target　Hg2+　from　hairpin　DNA.　The　liberated　target　Hg2+　initiated　the　next　cycling,　thereby　causing　the　conformational　change　of　numerous　hairpin　probes　from　the　stem-loop　DNA　structure　to　single-stranded　DNA.　Under　the　optimal　conditions,　the　fluorescent　intensity　of　the　as-produced　DNA-AgNCs　decreased　with　the　increasing　Hg2+　concentration　within　a　dynamic　range　from　0.1　nM　to　10　nM　with　a　detection　limit　(LOD)　of　24　pM.　Moreover,　the　low-cost　fluorescent　sensing　system　exhibited　high　reproducibility　and　good　specificity,　thus　representing　an　optional　sensing　platform　for　rapid　screening　of　Hg2+　in　environmental　water　samples.　(C)　2015　Elsevier　B.V.　All　rights　reserved.