In　this　study,　a　signal-off　photoelectrochemical　aptasensing　approach　was　designed　for　quantitative　screening　of　carcinoembryonic　antigen　(CEA)　by　using　cobalt　sulfide　nanoparticle-functionalized　cadmium　sulfide　nanoflowers　(Co9S8@CdS)　as　photoactive　matrix　and　CuS　nanoparticles　(NPs)　as　electronic　extinguisher,　coupling　with　target-induced　hybridization　chain　reaction　(HCR).　The　Co9S8@CdS　nanohybrids,　which　were　synthesized　using　a　two-step　thermal　process,　shorten　the　electron-migration　path　by　virtue　of　their　matched　and　close　band　positions,　thus　facilitating　carrier　separation　and　increasing　photoactivity.　In　the　sensing　process　of　CEA,　a　sandwiched　reaction　occurred　followed　by　the　smooth　implementation　of　the　HCR,　accompanied　by　the　introduction　of　a　huge　amount　of　CuS　NPs　on　the　photoelectrode　surface.　These　captured　CuS　NPs　increased　the　consumption　of　electron　donors　(ascorbic　acid,　AA)　and　excitation　light　energy　and　also　impeded　the　movement　of　AA　toward　the　electrode,　which　synergistically　led　to　an　obvious　decrease　in　photocurrent.　Under　optimum　conditions,　the　as-designed　aptasensor　exhibited　satisfactory　analytical　performance　for　the　target　CEA　with　a　dynamic　linear　range　from　0.02　to　40.0　ng　mL−1　and　a　detection　limit　of　7.4　pg　mL−1.　Besides,　this　sensor　possessed　high　specificity,　good　stability,　and　acceptable　accuracy.　The　current　results　suggest　that　our　proposed　strategy　might　have　broad　application　prospects　in　the　bioanalysis　of　disease-related　markers　and　early　disease　diagnosis.　©　2023　The　Royal　Society　of　Chemistry.