Here, an ultrasensitive electrochemiluminescence (ECL) immunosensor for the detection of cardiac troponin I (cTnI) was developed by using zeolitic imidazolate frameworks encapsulating spherical graphite crystals (CQDs@ZIF-8) as luminophore. Firstly, luminescent spherical graphite crystals (CQDs) were encapsulated in the zeolitic imidazolate framework (ZIF-8) nanocrystals. To improve the poor conductivity of CQDs@ZIF-8, Au nanoparticles were synthesized on the surface of CQDs@ZIF-8 to form AuNPs/CQDs@ZIF-8. Furthermore, L-cysteine (L-cys) as the coreactant of CQDs was immobilized on the AuNPs to enhance the ECL signal of CQDs. Then, the obtained L-cys/AuNPs/CQDs@ZIF-8 was introduced to construct an ultrasensitive ECL immunosensor for the detection of cTnI. As a result, the proposed immunosensor displayed excellent analytical performances for the detection-of-cTnI with a linear range from 1 fg mu L-1 to 10 pg mu L-1 and a detection limit of 033 fg mu L-1. (C) 2016 Elsevier B.V. All rights reserved.