This work reports the liposome-mediated in situ formation of the AgI/Ag/BiOI Z-scheme heterojunction on foamed nickel electrode for signal-on cathodic photoelectrochemical (PEC) bioanalysis. Specifically, in a proof-of-concept study, Ag nanoparticle-encapsulated liposomes were initially confined via the sandwich immunobinding and then processed to release numerous Ag+ ions, which were then directed to react with the BiOI/Ni electrode, resulting in the in situ generation of a AgI/Ag/BiOI Z-scheme heterojunction on the electrode. The enhanced cathodic signal could be correlated to the target concentration, which thus underlays a novel signal-on cathodic liposomal PEC bioanalysis strategy. Different from previous anodic liposomal PEC bioanalysis, this work features the first cathodic liposomal PEC bioanalysis on the basis of the in situ formation of a Z-scheme heterojunction. More generally, integrated with various biorecognition events, this protocol could serve as a common basis for addressing numerous targets of interest.