A novel label-free photoelectrochemical immunosensor was developed for the determination of prostate-specific antigen (PSA) based on fluorine-doped tin oxide (FTO) electrode modified with anatase and rutile titanium dioxide nanoparticles (TiO_2(a-r)) as a platform for the electrodeposition of bismuth sulfide (Bi₂S₃). The photoelectrochemical response of the TiO_2(a-r) platform sensitized with Bi₂S₃ for the ascorbic acid donor molecule (AA) was about 34-fold higher than that observed in the absence of Bi₂S₃. The Bi₂S₃/TiO_2(a-r)/FTO platform was modified with PSA antibodies to produce the anti-PSA/Bi₂S₃/TiO_2(a-r)/FTO immunosensor, which was incubated in solutions of PSA antigen to inhibit the photocurrent of the immunosensor for AA. The photocurrent of the anti-PSA/Bi₂S₃/TiO_2(a-r)/FTO immunosensor presented a linear relationship with the logarithm of the PSA concentration ranging from 1 pg mL⁻¹ to 100 ng mL⁻¹ with good sensitivity and a limit of detection of 0.870 pg mL⁻¹. The sensor was successfully employed for the determination of PSA in artificial blood plasma samples, with recoveries between 94.6 and 98.6%.