This　work　reports　a　novel　electrochemical　immunoassay　protocol　with　signal　amplification　for　determination　of　low-abundance　protein　(free　prostate-specific　antigen,　PSA,　used　as　a　model)　with　high　sensitivity　and　high　selectivity　by　coupling　metal　sulfide　(PbS)-based　nanolabels　with　cleavage　of　the　corresponding　lead　ion-induced　DNAzymes.　The　assay　mainly　consists　of　an　antigen-antibody　immunoreaction　with　metal　nanolabel　in　a　transparent　96-well　polystyrene　microplate,　the　release　of　metal　ions　from　the　nanolabel,　and　cleavage　of　metal　ion-induced　DNAzyme.　The　signal　is　amplified　by　the　labeled　redox　tag　(ferrocene)　on　the　DNAzyme-based　sensor.　In　the　presence　of　target　analyte,　the　sandwiched　immunocomplex　can　be　formed　between　the　primary　antibody　on　the　microplate　and　the　corresponding　metal　sulfide　nanolabel.　The　carried　nanolabel　can　release　numerous　metal　ions　by　acid,　and　induce　the　cleavage　of　the　corresponding　DNAzyme,　thus　resulting　in　the　change　of　electrochemical　signal.　Under　optimal　conditions,　the　DNAzyme-based　immunoassay　presents　an　obvious　electrochemical　response　for　the　detection　of　PSA,　and　allows　detection　of　PSA　at　a　concentration　as　low　as　0.1　pg　mL(-1).　Intra-assay　and　interassay　coefficients　of　variation　(CV)　were　less　than　9.5%　and　10%,　respectively.　No　significant　differences　at　the　0.05　significance　level　were　encountered　in　the　analysis　of　12　clinical　serum　specimens　between　the　developed　immunoassay　and　a　commercially　available　enzyme-linked　immunosorbent　assay　(ELISA).