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A signal-off type photoelectrochemical (PEC) immunosensor based on Ru(bpy) 3 2+ and Bi 2 S 3 co-sensitized ZnTiO 3 /TiO 2 polyhedra as matrix and SiO 2 /PDA-Au as the label of second antibody was proposed for the ultrasensitive detection of procalcitonin (PCT). The hollow ZnTiO 3 /TiO 2 polyhedra called zinc titanium composite hollow structures (ZTCHS) was prepared by hydrothermal method to enhance the utilization of visible light comparing with pure ZnTiO 3 or TiO 2. The unique structure endowed large specific surface areas and satisfying load capacity to ZTCHS. Ru(bpy) 3 2+ and Bi 2 S 3 were utilized to co-sensitize ZTCHS to further strengthen the PEC performance of ZTCHS. It was interesting that the dual-inhibition effects of SiO 2 /PDA-Au further enhanced the sensitivity of proposed PEC immunosensor. On the one hand, the steric hindrance of SiO 2 /PDA effectively restricted electron transfer. On the other hand, Au nanoparticles could absorb visible light to compete with the matrix material. Based on the above aspects, the proposed signal-off type PEC immunosensor possessed a wide linear range from 0.0001 ng mL−1 to 100 ng mL−1 and low detection limit (about 0.03 pg mL−1, S/N = 3), demonstrating the promising application of PEC immunosensor in analysis fields. ► Novel Ru (bpy) 3 2+ and Bi 2 S 3 sensitized ZTCHS polyhedra shows excellent PEC activity. ► The dual-inhibition effects of SiO 2 /PDA-Au reduce distinctly the photocurrent. ► A signal-off type PEC sensor achieves the ultrasensitive detection of procalcitonin. [ABSTRACT FROM AUTHOR]