In this work, a self-electrochemiluminous graphene oxide-capped Au@L012 nanocomposite was prepared as the label at carcinoembryonic (CEA) antibody to detect attomole CEA antigen. To maximize the luminescence intensity, L012 molecules (luminol analogue) were linked with poly(diallyldimethylammonium chloride) (PDDA) to form positive charged PDDA&L012 pairs, which were modified on negative charged Au@nafion nanoparticles to construct a Au@nafion@PDDA&L012 (Au@L012) complex. Graphene oxide with carboxyl groups was capped at Au@L012 complex through electrostatic interaction to serve as an effective matrix for the covalent attachment of CEA antibody. As compared with the traditional used Au nanoparticles modified with luminol, ∼740-fold increase of self-luminescence was observed from this new complex so that CEA antigen as low as 0.5 amol at electrode surface was measurable in the absence of any coreactant. Moreover, the nanocomposite was attached with CEA antigen at MCF-7 cells allowing the detection of CEA antigen from 72 cells. The success in the detection of surface antigen at small population of cells suggested the self-electrochemiluminescence nanocomposite as the new and biosafe label for the ECL immunoassay, which might push the application of ECL for the cellular immunoanalysis.