A simple photoelectrochemical (PEC) immunoassay based on an amino-terminated perylene derivative (PTCNH2) was developed for highly sensitive and specific detection of tumor necrosis factor-alpha (TNF-alpha). Simple grinding and sonication afforded a pi-pi stacked graphene oxide (GO)/PTCNH2 assembly exhibiting fast electron transfer kinetics and excellent photoelectric performance, and this assembly was applied as a PEC probe. The GO-PTCNH2 assembly provided not only a large surface area, fast electron transfer kinetics and abundant active sites for further biomolecule conjugation but also high PEC activity. A "signal-off" PEC immunoassay for TNF-alpha was developed by assembling GO-PTCNH2 on the electrode, followed by conjugation of anti-TNF-alpha with GO-PTCNH2 and subsequent capture of the target protein TNF-alpha. The linear detection range was from 10 pg/mL-100 ng/mL with a limit of detection (LOD) of 3.33 pg/mL. This method was also successfully applied for detecting TNF-alpha in human serum with recoveries ranging from 92,5% to 96.6% and a relative standard deviation of less than 9.99%. For the first time, this work reports a simple PEC immunoassay achieved by using PTC-NH2 as a photoelectrochemically active probe for the detection of a tumor biomarker. This assay could be applicable to the detection of other biomarkers for clinical diagnosis.