An enzyme electrocatalytic immunosensor based on functional composite nanofibers for sensitive detection of tumor suppressor protein p53 (AG(p53)) is developed. The carboxylated multi-walled carbon nanotube (MWCNT) doped nylon 6 (PA6) composite nanofibers (MWCNT-PA6) were prepared using electrospinning, which served as the nanosized backbone for thionine (TH) electropolymerization. The functional composite nanofibers (MWCNT-PA6-PTH) served as supporting scaffolds not only promotes electron transfer, but also increases the surface area to introduce a large amount of AG(p53) capture antibody (Ab(1)), thus increasing the detection sensitivity. After a sandwich immunoreaction, AG(p53) and horseradish peroxidase (HRP)-labeled detection antibody (HRP@Ab(2)) captured onto the electrode surface produced an amplified electrocatalytic response by the reduction of enzymatically oxidized polythionine (PTH) in the presence of hydrogen peroxide (H2O2). The increase of response current was proportional to the AGp53 concentration in the range of 2 pg mL(-1) to 2 ng mL(-1) and the detection limit was down to 1 pg mL(-1). This study provides new insight into the design of advanced electrospun nanofiber-based immunosensor for detection and analysis of a variety of proteins. It holds promise for the diagnosis of cancer development and monitoring of patient therapy. (C) 2015 Elsevier B.V. All rights reserved.