In this work, the eletrochemiluminescence (ECL) behavior of Cu2+/cysteine complexes and N-(aminobutyl)- N-(ethylisoluminol) (ABEI) functionalized gold nanoparticles combined with chitosan (Cu2+-Cys-ABEI-GNPs-CS) were studied by cyclic voltammetry and a double-step potential, which exhibited excellent ECL properties without any coreactant. It was found that the ECL intensity of Cu2+-Cys-ABEI-GNPs-CS could increase at least 1 order of magnitude compared with that of Cu2+-Cys-ABEI-GNPs. Furthermore, a coreactant-free and label-free ECL immunosensor has been established for the determination of early acute myocardial infarction biomarker copeptin based on luminescent immuno-gold nanoassemblys consisting of Cu2+-Cys-ABEI-GNPs-CS and immuno-gold nanoparticles prepared by connecting copeptin antibody with trisodium citrate stabilized gold nanoparticles. In the presence of copeptin, an obvious decrease in ECL intensity was observed due to the formation of antibody-antigen immunocomplex, which could be used for the determination of copeptin in the range of 2.0 × 10-14-1.0 × 10-11 mol/L with a detection limit of 5.18 × 10-15 mol/L. The detection limit of the ECL immunosensor is at least 2 orders of magnitude lower than that of sandwich immunoassays based on labeling technology. Also, the ECL immunosensor does not need any coreactant and avoids complicated labeling and purification procedure. It is ultrasensitive, simple, specific, and low-cost. This work reveals that the proposed luminescent immuno-gold nanoassemblies are ideal nanointerfaces for the construction of immunosensors. The proposed strategy may be used for the determination of other antigens if corresponding antibodies are available.