We　designed　a　signal-on　photoelectrochemical　(PEC)　immunoassay　for　the　sensitive　monitoring　of　prostate-specific　antigen　(PSA)　based　on　the　etching　reaction　of　hydrogen　peroxide　(H2O2)　toward　oxygen/phosphorus　co-doped　graphitic　C3N4/AgBr/MnO2　nanosheets　(OP-g-C3N4/AgBr/MnO2).　Initially,　glucose　oxidase　(GO(X))-labeled　detection　antibodies　were　introduced　into　the　capture　antibody-coated　microplate　with　a　sandwich-type　immunoreaction　in　the　presence　of　PSA.　Then,　the　as-generated　H2O2　from　the　decomposition　of　glucose　by　GO(X)　etched　the　manganese　dioxide　(MnO2)　nanosheets　into　manganese　ions　(Mn2+),　thereby　causing　the　exposure　of　the　underlying　OP-g-C3N4/AgBr.　Meanwhile,　H2O2　could　be　also　used　as　an　electron　scavenger,　and　restrain　the　recombination　of　the　electron　hole　pairs　of　OP-g-C3N4/AgBr.　Two　advantages　of　H2O2　enhanced　the　photocurrent　synergistically.　Under　optimum　conditions,　the　PEC　immunoassay　showed　high　sensitivity　toward　target　PSA　within　a　dynamic　working　range　of　0.05-50　ng　mL(-1)　with　a　limit　of　detection　of　17　pg　mL(-1).　In　addition,　our　system　possessed　high　specificity,　favorable　selectivity,　and　good　stability.　Relative　to　commercialized　PSA　ELISA　kits,　the　accuracy　of　our　strategy　was　acceptable.　More　importantly,　our　strategy　can　be　easily　extended　to　screen　other　biomarkers　by　controlling　the　corresponding　antibodies.　(C)　2021　Elsevier　B.V.　All　rights　reserved.