Early　detection　of　cancer　has　a　profound　impact　on　patient　survival　and　treatment　outcomes　considering　high　treatment　success　rates　and　reduced　treatment　complexity.　Here,　we　developed　a　portable　photoelectrochemical　(PEC)　immune　platform　for　sensitive　testing　of　alpha-fetoprotein　(AFP)　based　on　Pt　nanocluster　(Pt　NCs)　loaded　defective-state　g-C3N4　photon-electron　transducers.　The　broad　forbidden　band　structure　of　g-C3N4　was　optimized　by　the　nitrogen　doping　strategy　and　additional　homogeneous　porous　structure　was　introduced　to　further　enhance　the　photon　utilization.　In　addition,　the　in-situ　growth　of　Pt　NCs　provided　efficient　electron　transfer　catalytic　sites　for　sacrificial　agents,　which　were　used　to　further　improve　the　sensitivity　of　the　sensor.　Efficient　photoelectric　conversion　under　a　hand-held　flashlight　was　determined　by　the　geometry　of　the　transducer　and　the　energy　band　design,　and　the　portable　design　of　the　PEC　sensor　was　realized.　The　developed　sensing　platform　exhibited　a　wide　linear　response　range　(0.1–50　ng　mL−1)　and　low　limit　of　detection　(0.043　ng　mL−1)　for　AFP　under　optimum　conditions.　This　work　provides　a　new　idea　for　designing　portable　PEC　biosensing　platforms　to　meet　the　current　mainstream　POC　testing　needs.　©　2024　Elsevier　B.V.