The proof-of-concept　of　sensitive　electrochemical　immunoassay　for　the　quantitative　monitoring　of　human　epidermal　growth　factor　receptor　2　(HER2) is　reported.　The　assay　is　carried　out　on　iron　nitrogen-doped　carbon　(FeNC)　nanozyme-modified　screen-printed　carbon　electrode　using　chronoamperometry.　Introduction　of　target　HER2　can　induce　the　sandwiched　immunoreaction　between　anti-HER2　monoclonal　antibody-coated　microplate　and　biotinylated　anti-HER2　polyclonal　antibody.　Thereafter,　streptavidin-glucose　oxidase　(GOx)　conjugate　is　bonded　to　the　detection　antibody.　Upon　addition　of　glucose,　3,3′,5,5′-tetramethylbenzidine　(TMB)　is　oxidized　through　the　produced　H2O2　with　the　assistance　of　GOx　and　FeNC　nanozyme.　The　oxidized　TMB　is　determined　via　chronoamperometry.　Experimental　results　revealed　that　electrochemical　immunosensing　system　exhibited　good　amperometric response,　and　allowed　the　detection　of　target　HER2　as　low　as　4.5　pg/mL.　High　specificity　and　long-term　stability　are　acquired　with　FeNC　nanozyme-based　sensing　strategy.　Importantly,　our　system　provides　a　new　opportunity　for　protein　diagnostics.　Graphical　Abstract:　[Figure　not　available:　see　fulltext.]　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Austria,　part　of　Springer　Nature.