br Conclusions br In summary a NiFe O NTs
In summary, a NiFe2O4 NTs catalyzing oxygen evolution reaction promoted ratiometric ECL biosensor for the sensing of HE4 was de-veloped based on DBAE and lucigenin as the new ECL emitter unit for the first time. In this protocol, NiFe2O4 NTs with superior properties not only served as a matrix to load large amounts of Envision-Ab1 complex, but catalyzed the OER process to yield oxygen, leading to a significantly promoted ECL response of DBAE. Interestingly, Envision complex an-chored with substantial HRP could accelerate the decomposition of H2O2 to release O2%−, which enhanced the two ECL reaction of DBAE and lucigenin. Additionally, the h-BN nanosheets was revealed to be an effective probe scaffold for the first time in this strategy, which achieved the high loading of lucigenin and maintained the intense and stable ECL signal of lucigenin for its strong adsorption capability and excellent resistance to corrosion. Therefore, by virtue of the above features, a highly sensitive ratiometric ECL strategy was designed for the sensitive determination of HE4, which holds great promise in the early ovarian cancer monitoring and clinical diagnosis.
Appendix A. Supplementary data
 T. Ma, M. Zhang, Y. Wan, Y. Cui, L. Ma, Preparation of an acridinium ester-labeled antibody and its application in goldmag nanoparticle-based, ultrasensitive chemi-luminescence immunoassay for the detection of human Ifenprodil hemitartrate protein 4, Micromachines 8 (2017).  L. Lu, B. Liu, Z. Zhao, C. Ma, P. Luo, C. Liu, G. Xie, Ultrasensitive electrochemical immunosensor for HE4 based on rolling circle amplification, Biosens. Bioelectron. 33 (2012) 216–221.  C. Wang, X. Ye, Z. Wang, T. Wu, Y. Wang, C. Li, Molecularly imprinted photo-electrochemical sensor for human epididymis protein 4 based on polymerized ionic liquid hydrogel and gold nanoparticle/ZnCdHgSe QDs composite film, Anal. Chem. 89 (2017) 12391.  H.P. Peng, M.L. Jian, Z.N. Huang, W.J. Wang, H.H. Deng, W.H. Wu, A.L. Liu, X.H. Xia, W. Chen, Facile electrochemiluminescence sensing platform based on high-quantum-yield gold nanocluster probe for ultrasensitive glutathione detection, Biosens. Bioelectron. 105 (2018) 71–76.
 K. Liao, E. Meyer, T.N. Lee, A. Loercher, D. Sikkema, Inhibition of interleukin-5 induced false positive anti-drug antibody responses against mepolizumab through the use of a competitive blocking antibody, J. Immunol. Methods 441 (2017) 15–23.  P.T. Babar, A.C. Lokhande, M.G. Gang, B.S. Pawar, S.M. Pawar, H.K. Jin, Thermally oxidized porous NiO as an efficient oxygen evolution reaction (OER) electrocatalyst for electrochemical water splitting application, J. Ind. Eng. Chem. 60 (2017).
 S. Asadizadeh, M. Amirnasr, S. Meghdadi, F.F. Tirani, K. Schenk, Facile synthesis of Co 3 O 4 nanoparticles from a novel tetranuclear cobalt(III) complex. Application as efficient electrocatalyst for oxygen evolution reaction in alkaline media, Int. J. Hydrogen Energy 43 (2018).
 M.R. Karimi Pur, M. Hosseini, F. Faridbod, M.R. Ganjali, S. Hosseinkhani, Early detection of cell apoptosis by a cytochrome C label-Free electrochemiluminescence aptasensor, Sens. Actuators B Chem. 257 (2018) 87–95.  M.R.K. Pur, M. Hosseini, F. Faridbod, M.R. Ganjali, Highly sensitive label-free electrochemiluminescence aptasensor for early detection of myoglobin, a biomarker for myocardial infarction, Microchim. Ichnoanal. Acta 184 (2017) 3529–3537.  M.R. Pur, M. Hosseini, F. Faridbod, A.S. Dezfuli, M.R. Ganjali, A novel solid-state electrochemiluminescence sensor for detection of cytochrome c based on ceria nanoparticles decorated with reduced graphene oxide nanocomposite, Anal. Bioanal. Chem. 408 (2016) 7193–7202.
 S. Hussain, M.M. Tavakoli, A. Waleed, U.S. Virk, S. Yang, A. Waseem, Z. Fan, M.A. Nadeem, Nanotextured Spikes of alpha-Fe2O3/NiFe2O4 composite for effi-cient photoelectrochemical oxidation of water, Langmuir 34 (2018) 3555–3564.  A. Sudhaik, P. Raizada, P. Shandilya, P. Singh, Magnetically recoverable graphitic carbon nitride and NiFe 2 O 4 based magnetic photocatalyst for degradation of oxytetracycline antibiotic in simulated wastewater under solar light, J. Environ. Chem. Eng. (2018).
Jiani Wang received her Bachelor's degree in 2017 from Baoji University of Arts and Sciences, China. She is working for her Master’s degree in Fujian Normal University and investigating focus on the application of biosensors.
Jianrong Song received his B.S. in clinical medicine at 1998 from Fujian Medical University, China. He is currently an associate chief physician at Fujian Provincial Maternity and Children's Hospital. His investigations focus on the gynecologic oncology for nearly 20 years.