This study investigated the morphological effects of vertically grown ZnO nanorods as bio-immobilized substrates for horse immunoglobulin (IgG) antigen. A simple and novel one-step process of antigen immobilization was developed. It was to apply horse antigen solution on the surface of ZnO nanorods as substrates by drying method at room temperature. The hydro-stability assessment of the immobilized antigen by FTIR spectroscopy was executed to determine its residual activity with reduced intensity. The design was to evaluate its specific functional groups of antigen in view of the absorption peak observed at a wave number of 1550 cm(-1) of water immersion time in calculation of the ratio. The results showed that the ratio of residual activity of horse antigen immobilized on ZnO nanorods substrates still presented more than 85% over the tip region in which the diameter was less than 65 nm. And it approached nearly 100% within the tip area of 28 nm in diameter on needle-like ZnO nanorods soaked in water for 2 h. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3559465] All rights reserved.