Development　of　accurate　analytical　protocols　for　cancer　biomarkers　is　used　for　the　initial　prescreening　of　malignant　tumors,　disease　surveillance,　and　efficacy　assessment　with　significant　clinical　benefits.　In　this　work,　we　reported　a　liposome-mediated　signal-off　photoelectrochemical　(PEC)　immunoassay　for　the　sensitive　detection　of　carcinoembryonic　antigen　(CEA)　using　ternary　transition　metal　sulfide　CuS/ZnCdS　as　the　photoactive　material.　Good　photocurrents　were　acquired　on　the　basis　of　specific　oxidation　reaction　of　dopamine　on　the　CuS/ZnCdS.　The　energy　band　relationship　of　CuS/ZnCdS　was　determined,　and　the　well-matched　oxidation　potential　of　dopamine　was　verified.　To　achieve　accurate　recovery　of　low-abundance　CEA,　systematic　PEC　evaluation　from　human　serum　samples　was　performed　by　combining　with　classical　immunoreaction　and　liposome-induced　dopamine　amplification　strategy　with　high　stability　and　selectivity.　Under　optimum　conditions,　PEC　immunoassay　displayed　good　photocurrent　responses　toward　target　CEA　with　a　dynamic　linear　range　of　0.1–50　ng/mL　with　a　detection　limit　of　31.6　pg/mL.　Importantly,　this　system　by　combining　with　a　discussion　of　energy　level　matching　between　semiconductor　energy　bands　and　small-molecules　opens　a　new　horizon　for　development　of　high-efficient　PEC　immunoassays.　©　2025