Lead　pollution　presents　a　significant　threat　to　ecological　systems　and　human　health,　underscoring　the　urgent　need　for　highly　sensitive　detection　methods.　Herein,　we　introduce　a　novel　DNA　concatemer-encoded　CRISPR/Cas12a　fluorescence　sensor　(MDD-Cas12a)　for　sensitive　detection　of　Pb2+　based　on　DNAzymes.　To　accomplish　this,　we　designed　a　substrate　strand　containing　a　long　DNA　concatemer　encoding　multiple　protospacer　adjacent　motifs　(PAMs)　and　protospacer　sequences　for　activation　of　the　CRISPR/Cas12a　system.　The　DNA　concatemer　was　subsequently　anchored　to　the　surface　of　magnetic　beads　(MBs)　to　fabricate　a　MBs-DNA　concatemer　nanoprobe.　In　the　presence　of　Pb2+,　the　DNAzyme　structure　catalyzes　the　cleavage　of　the　substrate　strand,　leading　to　the　release　of　DNA　concatemers.　Following　magnetic　separation,　the　released　DNA　concatemers　significantly　activate　the　non-specific　trans-cleavage　activity　of　the　Cas12a/crRNA　complex.　The　fluorescence　reporter　DNA　is　then　completely　cleaved　by　the　activated　Cas12a/crRNA　complex,　and　the　Pb2+　concentration　in　the　sample　can　be　quantified　by　measuring　the　fluorescence　signal.　By　harnessing　the　specific　recognition　capability　of　DNAzymes　for　Pb2+,　the　programmability　of　DNA　concatemers,　and　the　self-amplification　features　of　the　CRISPR/Cas12a　system,　the　MDD-Cas12a　platform　demonstrates　high　sensitivity　and　specificity　for　detecting　Pb2+　in　milk　and　lake　water　samples.　©　2025　The　Royal　Society　of　Chemistry.