Ovarian cancer is the foremost cause of death in women in the category of gynaecological malignancy. Fostering a high survival rate requires early prognosis and therefore needs ultrasensitive detection of a biomarker such as fibronectin, a glycoprotein in the extracellular matrix having a high prognostic value for ovarian cancer. Thus, such an application needs a cost-effective sensing material that possesses a high surface to volume ratio, good conductivity, and strong affinity towards biomolecules. Smartly engineered bio-wastes have shown notable potential in biosensors due to their innate biocompatibility albeit seldom utilized due to poor biomolecular interaction (sensitivity). In this work, a novel biosensor, based on sweet corn husk (bio-waste) derived porous carbon is demonstrated for a label-free ultra-detection of fibronectin protein. The reported porous carbon has high significance owing to high specific surface area (500 m2 g−1), excellent conductivity, and high affinity toward biomolecules due to the inherent presence of silica on the carbon surface. The announced biosensor presents a broad range (100 fg mL−1–10 μg mL−1) of detection with a sterling sensitivity (124.5 (KΩ/µg mL−1)/cm2) and a LOD of 129 fg mL−1. Further, it shows excellent selectivity, interference resistance response, reproducibility, high linearity and good stability, hence exhibiting a towering potential for real sample tests. © 2021