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We report an electroactive 3-dimensional graphene-multi walled carbon nanotube (G-MWCNT) hybrid prepared using a one step chemical vapor deposition (CVD) method with acetylene as a precursor source, transferred over a glassy carbon electrode (GCE) as a biomolecular immobilization material, for the construction of a bioelectrode. G-MWCNT/GCE was covalently immobilized with human cardiac troponin antibody (anti-cTnI) through a molecular bi-linker, 1-pyrene butyric acid N-hydroxysuccinimide ester (PyBuNHS), and characterized by spectroscopy and electrochemical techniques. The bio-analytical performance of the electrode was investigated using electrochemical impedance spectroscopy (EIS) by fitting the impedance response of the electrode with an optimal fitted equivalent circuit model for the quantitative detection of human cardiac troponin (cTnI) in human serum. A low value of exponent 'n' (n ¼ 0.44) observed in a constant phase element of the impedance of the G-MWCNT/GCE hybrid electrode indicated a heterogeneous microstructure surface that exhibited diffusive characteristics but showed dominant charge transfer characteristics (R et ) with n ¼ 0.88 upon biomolecular immobilization and subsequent immunoreaction with target cTnI in the low frequency region of <1 Hz, showing a good biocompatibility. The bioelectrode exhibited a linear impedance response to cTnI in a wide range of 0.001-10 ng mL À1 in human serum with a low detection limit of 0.94 pg mL À1 and a sensitivity of 63.5 U cm 2 per decade.

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