A　novel　signal　amplification　strategy　based　on　Cu2+-dependent　DNAzyme　was　developed　for　sensing　Cu2+　ion　by　combining　hybridization　chain　reaction　(HCR)　with　fluorescence　resonance　energy　transfer　(FRET)　technique.　In　the　presence　of　Cu2+　ion,　the　substrate　strands　of　Cu2+-dependent　DNAzyme　immobilized　on　magnetic　beads　were　specifically　cleaved　and　released.　The　released　strands　initiated　the　HCR　process　of　hairpin　H1　and　H2　labeled　with　FAM　as　the　donor　and　TAMRA　as　the　acceptor,　respectively.　Long　nicked　dsDNA　structures　were　self-assembled　to　bring　the　donor　and　the　acceptor　in　close　proximity,　resulting　in　a　FRET　process.　The　relative　ratio　of　fluorescent　intensities　of　the　acceptor　and　donor　was　used　to　quantitatively　detect　Cu2+　ion　with　a　limit　of　detection　of　0.5　nmol　L-1.　This　proposed　biosensor　was　applied　to　detect　Cu2+　ion　in　tap　water　with　satisfactory　results.　(C)　2016　Elsevier　B.V.　All　rights　reserved.