Herein,　we　reported　a　novel　photoelectrochemical　immunoassay　method　based　on　a　target-triggered　on/off　signal　of　the　ultra-structured　Bi2O2S　(BOS)　photoanode　system　for　the　sensitive　testing　of　carcinoembryonic　antigens　(CEAs)　in　serum　samples.　Well-defined　three-dimensional　sheet-like　self-assembled　flower-like　Bi2O2S　superstructures　were　obtained　using　a　time-controlled　hydrothermal　method.　Such　well-shaped　multifaceted　surfaces　were　considered　to　be　good　laser　cavity　mirror　surfaces　for　multifaceted　reflection　and　refraction　of　excitation　light　in　the　material.　An　elegant　enzyme　biocatalytic　strategy　was　introduced　into　the　constructed　detection　model　to　sensitively　detect　CEAs.　The　substrate　4-chloro-1-naphthol　(4-CN)　was　oxidized　to　4-chloro-hexadienone　(4-CD)　under　the　formation　of　target-triggered　immune　complexes　against　mAb1　and　peroxidase-modified　mAb2.　Subsequently,　4-CD　produced　by　the　biocatalytic　precipitation　reaction　was　transferred　to　the　photoanodes　of　Bi2O2S　nanoflowers　(BOS　NFs)　to　burst　their　photoelectric　signals,　thus　achieving　the　quantification　of　CEAs.　Through　optimization　of　the　conditions　of　the　immunization　protocol,　a　good　negative　photocurrent　response　to　the　target　CEA　was　found　in　the　wide　range　of　0.02-50　ng　mL−1　with　a　detection　limit　of　11.2　pg　mL−1.　Impressively,　the　reported　biocatalytic　PEC　sensing　strategy　on　superstructures　is　comparable,　or　superior,　to　the　gold　standard　ELISA　kit　in　terms　of　sensitivity　and　the　target　response　range.　This　study　presents　a　target-mediated　PEC　immunoassay　for　biocatalytic　precipitation　based　on　a　self-assembled　superstructure　of　Bi2O2S,　providing　a　fresh　scheme　for　the　analysis　of　disease-related　markers.　©　2022　The　Royal　Society　of　Chemistry.