A novel photoelectrochemical (PEC) cytosensor for the ultrasensitive detection of circulating tumor cells (CTCs) was developed. The bio-inspired reduced graphene oxide (rGO) honeycomb film photoelectrode was fabricated via a "breath figure" method, followed by the self-assembly of a Bi2S3-MoS2 heterojunction. The resulting Bi2S3-MoS2 heterojunction-modified rGO honeycomb film was employed as a sensing matrix for the first time. Compared to the smooth rGO film, the significant enhanced photocurrent of the photoelectrode under visible light was attributed to its improved visible light absorption, increased surface area and enhanced separation efficiency of photo-generated electron-hole pairs, which met the requirements of the PEC sensor for detecting larger targets. By virtue of the photocurrent decrease due to the steric hindrance of MCF-7 cells, which were captured by an aptamer immobilized on the surface of the photoelectrode, a cytosensor for detecting CTCs was achieved, showing a wide linear range of 10-1 × 105 cells per mL and a low detection limit of 2 cells per mL. Furthermore, MCF-7 cells in human serum were determined by this PEC biosensor, exhibiting great potential in the clinical detection of CTCs.