Exploiting　innovative　strategies　with　signal　amplification　in　photoelectrochemical　(PEC)　biosensing　systems　to　realize　sensitive　screening　of　low-abundance　proteins　has　become　one　of　the　mainstream　research　orientations.　Herein　we　reported　a　new　strategy　to　amplify　photocurrent　signal　employing　a　photocatalyst-electrolyte　effect　in　alkaline　media　for　the　sensitive　monitoring　of　prostate-specific　antigen　(PSA)　using　snowflake-liked　CdS@ZnIn2S4　heterojunction　as　photosensitizer.　In　this　strategy,　both　the　band-edge　position　and　surface　redox　reaction　process　were　subtly　altered　by　modulating　the　alkalinity　of　electrolyte.　The　hydroxyl　anions　(OH-　)　from　NaOH　could　be　oxidized　to　hydroxyl　radicals　(.OH)　by　the　holes　in　CdS@ZnIn2S4,　thus　accelerating　the　scavenging　of　holes　and　promoting　the　photocurrent.　Based　on　the　above-mentioned　mechanism,　a　sensitive　split-type　glucose　oxidase-mediated　PEC　immunosensor　for　PSA　detection　was　fabricated.　Upon　target　PSA　introduction,　the　glucose　acid　was　generated　through　the　sandwich-type　immunoreaction　to　affect　the　alkalinity　of　PEC　detection　environment,　thereby　suppressing　the　photocurrent　intensity.　The　CdS@ZnIn2S4-based　PEC　immunosensor　exhibited　satisfactory　photocurrent　responses　with　a　good　linear　range　of　0.04-40　ng　mL(-1)　at　a　limit　of　detection　of　14　pg　mL(-1).　Significantly,　this　research　not　only　introduces　an　effective　strategy　to　detect　PSA　with　good　sensitivity　and　specificity,　but　also　provides　a　new　insight　to　amplify　the　signal　by　regulating　the　electrolyte.