Label-free electrochemical immunosensors based on screen-printed carbon electrodes are a promising tool for performing fast, simple and economical detection of cancer biomarkers.However, despite the potential of these devices, some limitations, such as their low sensitivity, need to be overcome before their widespread use as technology for clinical analysis. Herein, we proposed different strategies to modify screen-printed carbon electrodes, aiming to improve the analytical signal and the surface area for the immobilization of antibodies, which are two essential parameters for reaching good analytical performance in label-free immunosensors. We explored the application potential of carbon black and NiFe 2 O 4 nanoparticles, two low-cost nanomaterials with excellent electrochemical properties, which remain relatively unexplored in the construction of electrochemical immunosensors. In a first approach, an immunosensor was developed for detecting the carbohydrate antigen CA 19-9 using electrodes modified with composites of carbon black and the polyelectrolytes polyethyleneimine and polyacrylic acid. The immunosensor exhibited a low detection limit of 0.07 U mL − 1 , in addition to an excellent fabrication reproducibility, stability and selectivity.The proposed device showed good correlation with commercial immunoassays in the determination of CA 19-9 in cell lysates and human serum samples from pancreatic cancer patients. An immunosensor for detecting the tumor protein p53 was also developed, using electrodes modified with films of polyethyleneimine and NiFe 2 O 4 nanoparticles. The analytical parameters of the devices are among the best reported in the literature for determination of p53, with a low detection limit of 5 fg mL −1 . Also, the immunosensors showed an excellent selectivity toward p53 detection in fetal bovine serum, saliva and cell lysate samples. The platforms proposed herein combined the numerous advantages of screenprinted electrodes with the excellent properties of the studied nanomaterials, allowing the development of low-cost (˂BRL$ 4/ test) and disposable devices with excellent analytical performance, which can be adapted for the detection of several disease markers.