A　new　signal-amplification　strategy　based　on　copper(II)　(Cu2+)-dependent　DNAzyme　was　developed　for　sensitive　impedimetric　biosensing　of　Cu2+　in　aqueous　solution　by　coupling　with　target-induced　formation　of　hemin/G-quadruplex-based　DNAzyme　and　enzymatic　catalytic　precipitation　technique.　Initially,　the　target　analyte　cleaved　the　Cu2+-specific　DNAzyme　to　generate　an　initiator　strand　on　the　sensor.　Thereafter,　the　initiator　strand　underwent　an　unbiased　strand-displacement　reaction　between　hairpin　probes　in　turn　to　construct　a　nicked　double-helix,　accompanying　the　formation　of　hemin/G-quadruplex　DNAzyme　on　the　long　duplex　DNA.　The　newly　formed　DNAzyme　could　oxidize　the　4-chloro-1-naphthol　(4-CN)　to　produce　an　insoluble　precipitation　on　the　sensor,　thus　resulting　in　a　local　alteration　of　the　conductivity.　Under　the　optimal　conditions,　the　resistance　increased　with　the　increasing　Cu2+　in　the　sample,　and　exhibited　a　wide　dynamic　working　range　from　0.1pM　to　5.0nM　with　a　detection　limit　of　60fM.　The　methodology　also　displayed　a　high　selectivity　for　Cu2+　relative　to　other　potentially　interfering　ions　owing　to　the　highly　specific　Cu2+-dependent　DNAzyme,　and　was　applicable　for　monitoring　Cu2+　in　real　river　samples.　Thus,　our　strategy　has　a　good　potential　in　the　environment　surveys.　©　2015　Elsevier　B.V.