Nitric oxide (NO) is an important bio-regulatory and signaling molecule associated with various physiological and pathophysiological pathways, but its sensitive real-time detection is still very challenging due to the low concentration, large diffusivity and fast decay in biological samples. Here an antimony tetroxide (Sb2O4) nanoflowers/reduced graphene oxide (rGO) nanocomposite is synthesized via a facile and eco-friendly solvothermal method to merit-combine highly electroactive Sb2O4 nanoflowers with large surficial rGO component for a strong synergistic effect on oxidation of NO. Results demonstrate that the Sb2O4/rGO-based sensor has a low detection limit, high sensitivity, excellent selectivity and fast response for NO detection. The real-time detected NO released from living cells showed significant difference between normal and tumor cells. The Sb2O4 nanoflowers/rGO nanocomposite sensor holds a great promise for important applications in biomedical research fields and clinical diagnosis. (C) 2020 Published by Elsevier Inc.