In this study, a label-free electrochemical biosensor system based on a disposable indium tin oxide polyethylene terephthalate (ITO-PET) electrode modified with the 11-(triethoxysilyl) undecanal (11-TESU) agent was developed for the detection of tumour necrosis factor-alpha (TNF-α) in serum. The developed biosensor was observed with electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) techniques, square wave voltammetry (SWV) and single frequency impedance (SFI) technique which is utilized for the specific interaction between anti-TNF-α and TNF-α antigen. In addition, scanning electron microscopy was used to look at how the morphology of each ITO-PET surface changed (SEM). All parameters such as 11-TESU concentration, anti-TNF-α concentration and anti-TNF-α incubation time, were optimized. The biosensor system was characterized by measuring its linear determination range, repeatability, reproducibility, reusability, storage stability, and surface coverage. The TNF-αelectrochemical biosensor showed high levels of repeatability and reproducibility as well as a large dynamic range of detection (from 0.03 pg mL-1 to 3 pg mL-1). The LOD and LOQ for the biosensor were extremely low at 1x10-4 pg mL-1 and 5x10-4 pg mL-1, respectively. It was applied to real samples to determine whether the proposed biosensor would be useful in clinical settings.