This paper demonstrates an ultrasensitive microfluidic biochip nanoengineered with microporous manganese-reduced graphene oxide nanocomposite for detection of cardiac biomarker, namely human cardiac troponin I. In this device, the troponin sensitive microfluidic electrode consisted of a thin layer of manganese-reduced graphene oxide (Mn3O4-RGO) nanocomposite material. This nanocomposite thin layer was formed on surface of a patterned indium tin oxide substrate after modification with 3-aminopropyletriethoxysilane and was assembled with a polydimethylsiloxane-based microfluidic system. The nanoengineered microelectrode was functionalized with antibodies specific to cardiac troponin I. The uniformly distributed flowershaped nanostructured manganese oxide (nMn3O4) onto RGO nanosheets offered large surface area for enhanced loading of antibody molecules and improved electrochemical reaction at the sensor surface. This microfluidic device showed an excellent sensitivity of log [87.58] kΩ/(ng mL-1)/cm2 for quantification of human cardiac troponin I (cTnI) molecules in a wide detection range of 0.008-20 ng/mL. This device was found to have high stability, high reproducibility, and minimal interference with other biomarkers cardiac troponin C and T, myoglobin, and B-type natriuretic peptide. These advantageous features of the Mn3O4-RGO nanocomposite, in conjunction with microfluidic integration, enabled a promising microfluidic biochip platform for point-of-care detection of cardiac troponin. © 2017 American Chemical Society.