Abstract: The author describes a voltammetric sensor for the simultaneous determination of formaldehyde and ammonia using rGO/ZnO composite micro-dumbbell shaped rods. A facile hydrothermal technique was adopted to synthesize rGO/ZnO composite based micro-dumbbell shaped rods. The potential application based on obtained product has been employed as electrochemical sensor towards the detection of ammonia and formaldehyde using hexamine. For performing an electrochemical sensing application, glassy carbon electrode was modified with rGO/ZnO composite rods and analysed for the formation of multiple peaks thus emphasizing the detection of formaldehyde and ammonia using hexamine. Hexamine is toxic food preservative when it dissolutes in saline medium containing pH 7.4 emits ammonia and formaldehyde. The crystallinity property has been examined using X-ray diffraction technique revealing composite rods (rGO/ZnO) with 29.5 nm were lesser than ZnO NPs (38.33 nm). The surface morphology was investigated by scanning electron microscopy (SEM). In order to examine limit of detection (LOD) and sensitivity, cyclic voltammetry was carried out to determine the formaldehyde and ammonia. The voltammetric results revealed three different redox peaks with increased hexamine concentrations in which 0.4 V for formaldehyde, 0.13 V for ammonia and ~ 0.3 V for Zn2+ ions. The calibrated curve for ammonia with LOD and LOQ was found to be 0.1 µM and 0.9 µM and for formaldehyde with 0.023 µM and 0.07 µM respectively. Based on investigated results, the modified electrode was applied to the determination of ammonia and formaldehyde in urine samples (real-time analysis) and the results proved that the method is sensitive and can be an alternative to chromatographic and spectroscopic techniques. Graphic Abstract: [Figure not available: see fulltext.] © 2019, Springer Science+Business Media, LLC, part of Springer Nature.