A mitochondrial redox protein cytochrome c reductase (CcR) based NO2─ biosensor. SAM functionalized GNP-PPy enhanced the sensitivity of NO2─ determination. ARM CORTEX M3 microcontroller based portable electrochemical analyzer for NO2─. NO2─ levels were further measured in hypoxia induced H9c2 cardiomyoblasts cells. A promising direct sensing method as an alternative for point-of-care applications.