Recently　emerged　Z-scheme　heterostructure-based　immunoassays　have　presented　new　opportunities　for　photoelectrochemical　(PEC)　biosensing　development.　Here,　we　described　a　tunable　signal-on　PEC　biosensor　for　the　detection　of　cardiac　troponin　I　(cTnI),　which　exploited　a　competitive　absorption　effect　between　Cu(II)　ions　and　a　Zr　metal-organic　framework　(Zr-MOF)　constructed　on　TiO2　nanorods　(Cu2+@Zr-MOF@TiO2　NRs).　Water-stable　Zr-MOF　was　coated　onto　TiO2　NRs　on　fluorine-doped　tin　oxide　to　form　a　Z-scheme　heterostructure　substrate　(Zr-MOF@TiO2　NRs),　which　exhibited　a　high　photoelectric　response.　Cu2+@Zr-MOF@TiO2　NRs,　constructed　by　loading　Cu(II)　ions　onto　the　architecture　of　Zr-MOF　by　electrostatic　interaction,　demonstrated　a　low　background　signal.　After　sandwich　immunorecognition　within　a　96　well　plate,　H2S,　generated　by　confined　alkaline　phosphatase　on　zeolitic　imidazolate　framework-8,　was　directed　to　react　with　Cu(II)　ions　to　form　CuS.　This　resulted　in　an　in　situ　change　in　the　photoelectrode　and　an　enhanced　photoelectric　signal.　The　developed　PEC　biosensing　platform　exhibited　high　sensitivity　and　selectivity　for　the　cTnI　immunoassay　with　a　detection　limit　of　8.6　pg/mL.　The　Z-scheme-based　competition　absorption　modulation　of　photoelectrochemistry　provides　a　new　strategy　for　general　PEC　biosensing　development.