This article reports the effects of natural plant proteins on the morphology of zinc oxide nanoparticles (ZnONPs) prepared via a precipitation method. Green synthesised ZnONPs have a wide range of uses such as biomedical applications, water purification, optical devices and gas sensors. The non-toxic and economical technique described in this article is favourable for large-scale production too. ZnONPs were produced from a zinc acetate precursor with dye extract of Ixora Coccinea (IC) leaves as a capping agent. The as-prepared ZnONPs were characterised by X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV-visible (UV-vis), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. The XRD analysis showed an average crystallite size of 23 nm. The SEM analysis revealed a reduction in aggregation of ZnO crystallites due to addition of dye extracts of IC. EDX and UV-vis results confirmed the formation of pure ZnONPs. Finally, the gas sensing properties of ZnO films, prepared by doctor blade method, were used to detect ethanol vapour. The results showed gas response ratios of 28.7 and 5.4 at 800 ppm and 40 ppm exposure, respectively. Furthermore, the response time and recovery time were found to be 24 sec and 47 sec, respectively at 200 ppm exposure of ethanol vapour.