This paper reports a microfluidic nitrate sensor using a graphene foam (GF) based electrode modified by titanium dioxide nanofibers (nTiO ₂ ) and nitrate reductase enzyme molecules. The porous structure of GF allows for an easy access of nTiO ₂ and enzyme molecules and attach onto the interior surfaces of GF scaffolds. This provides enhanced surface area and loading capability of enzymes for catalytic reaction with nitrate ions in soil extracts. This sensor offers a superior sensitivity of 0.316 kΩ/μM/cm ² , fast detection time (~87s), and a high selectivity to nitrate ions even in presence of many interfering ions in the soil.