In recent years, need for rapid, reliable, and low-cost protein biomarker screening has tremendously boosted research into the development of electrochemical immunosensors. In this line, here we report on rapid fabrication and proof-of-concept demonstration of a hyper-branched gold nanostructure (ns@gold) based electrochemical immunosensor for detection of protein biomarker at pg/mL level. We have optimized a simple direct electrochemical process to rapidly generate uniformly distributed high surface area ns@gold within 30 min. These 3D ns@gold show ∼ 8-times enhancement in conductivity and also a rapid surface functionalization via self-assembled monolayers (SAM) of mercaptoundecanoic acid within 45 min. Protein estimation data showed around 94 % immobilization efficiency on the ns@gold surface in comparison to 28.4 % on plain gold surface. A fast SAM formation and quick antibody immobilization steered the assay timing within 4 h. As a proof-of-concept, we used an antibody-antigen interaction for the detection of epithelial growth factor receptor (EGFR) protein. Voltammetric data for the target EGFR receptor resulted a linear working range of 10 pg/mL to 100 ng/mL with a low limit-of-detection of 6.9 pg/mL. High selectivity in detecting target proteins from a pool of non-target proteins using breast cancer cell lines was also demonstrated along with good stability and reusability.