Photoelectrochemical　(PEC)　immunoassay　has　been　widely　developed　for　biomarker　detection,　but　most　include　heavy　and　expensive　instruments　that　are　not　suited　for　portable　and　on-site　detection.　In　this　work,　the　PEC　immunoassay　platform　for　mobile　phones　was　reported　for　flexible,　rapid,　low-cost　detection　of　carcinoembryonic　antigen　(CEA).　The　PEC　detection　platform　was　successfully　composed　of　disposable　screen-printed　carbon　electrodes,　a　micro-electrochemical　workstation,　a　flashlight　(the　excitation　light　source),　and　a　smartphone　with　a　companion　software　with　a　micro-electrochemical　workstation　for　rapid　and　on-site　detection　of　target　biomarkers.　In　this　portable　smartphone-based　PEC　system,　the　S-scheme　heterojunction　BiOCl/CuBi2O4　was　effectively　excited　due　to　the　efficient　electron　transfer　rate　and　excellent　photocurrent　response　under　visible　light.　Specifically,　the　sandwich-type　immunoreaction　for　capturing　target　biomarkers　introduced　alkaline　phosphatase　(ALP)　labeled　gold　nanoparticles　(Au　NPs).　The　addition　of　CEA　increased　the　ascorbic　acid　(AA)　content　and　enhanced　the　photocurrent.　The　proposed　immunoassay　presented　a　good　linear　with　the　logarithm　of　CEA　concentrations　range　within　0.01–40　ng　mL−1,　and　the　detection　limit　of　3.5　pg　mL−1　(S/N　=　3).　Therefore,　the　portable　detection　platform　offered　an　implementable　approach　to　the　development　of　miniaturized　and　portable　photoelectrochemical　detectors　and　on-site　detection　technology.　©　2023　Elsevier　B.V.