When free diffusing ammonia begins to dissolve into a reaction precursor solution, a gas/liquid interface formed. Three-dimensional (3D) network iron oxide (i-Fe3O4) was synthesized at the interface without the protection of any inert gas at room temperature. This is the first time ammonia vapor method be used to prepare nano iron oxide at a gas/liquid interface. Scanning electron microscope results of it indicated that 3D network i-Fe3O4 is an assembly of nanowires and its properties are quite similar to spherical Fe3O4 nanoparticle. Energy dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectra were used to confirm the presence of Fe3O4. Electrochemical methods were employed to investigate the sensing properties for the electrocatalytic oxidation of hydrazine hydrate at the i-Fe3O4/glassy carbon electrode (GCE). The sensor displayed a response time less than 2s. a sensitivity of 152 mu A mM(-1) cm(-2) and the linearity of 0.1 to 600 mu M with a detection limit of 0.05 mu M (S/N = 3). (C) 2012 Elsevier Ltd. All rights reserved.