The antibody immobilization with low-cost materials and label-free methods are a challenge for the fabrication of biosensor devices. In this work, it was developed a strategy for antibody immobilization on ZnO TFTs over polyethylene terephthalate (PET) as a recyclable plastic substrate. In a first approach we performed a detection of 1x10⁸ enteropathogenic E. coli UFC/mL used as our testing model. Antibodies were biofunctionalized using a label-free strategy for bacterial detection. This strategy was able to couple the physics of transistors, the film deposition at low temperature and the binding of the biological recognition element (antibody) without affecting the functionality of the device. Fourier Infrared spectroscopy (FTIR) is a non-destructive technique used for monitoring the complete process, showing the characteristic signals (amide I, II and S-S) related to the antibody immobilization on ZnO-TFTs. Moreover, the transfer characteristics allowed us to observe the device before and after the immobilization and the changes in the shift of the threshold voltage V_t. The use of a recyclable plastic substrate PET enables the compatibility with flexible electronics that could contribute for a low-cost biosensor useful in rural communities that do not have the necessary infrastructure and trained personnel for pathogenic bacterial detection in food or water. The development of this technology has the versatility to be extrapolated to different testing models, allowing the early detection of emerging diseases (bacterial or viral), and also it provides the opportunity to end-users for self-testing.