Squamous cell carcinoma antigen (SCCA) has great diagnostic values for its high specificity (90-96%) in diagnosis of squamous cell carcinoma especially cancers, where electrochemical immunoassay is powerful for its accurate and reliable detection of specific tumor biomarkers at very low levels. In this work, well-defined three-dimensional dendritic core-shell rhodium@platinum-cobalt nanocrystals (Rh@PtCo NCs) were facilely prepared via a simple one-pot solvothermal strategy. Taking advantage of dramatically enhanced catalytic activity of the Rh@PtCo NCs for catechol oxidation, a label-free electrochemical immunosensor was developed for highly sensitive assay of SCCA. Under optimal conditions, the electrochemical signals were linearly correlated with the logarithm of the SCCA concentration, showing a broad linear range from 0.0001 to 10.0 ng mL(-1) and a ultralow detection limit of 0.04 pg mL(-1) (S/N = 3). The resultant immunosensor was further exploited for actual analysis of serum samples with convinced results. This immunosensor has good expectation in actual samples analysis and provides a universal approach for detection of other tumor markers and disease surveillance. (C) 2019 Elsevier Inc. All rights reserved.