The ZnO material exhibits a rich family of nanostructures, which show great potential for the sensitivity improvement of optical detection systems. In this work, ~350 nm ZnO nanowires (ZnONWs) were electrochemically deposited on ZnO and indium tin oxide coated glass (ZnONWs/ZnO/ITO/glass) substrate. ZnO-NWs were modified with N-(3-Aminopropyl)triethoxysilane (APTES) for covalent bovine serum albumin (BSA) immobilization. The studies were performed using spectroscopic total internal reflection ellipsometry (TIRE) setup based on the Kretschmann configuration. The refractive index dispersion of ZnO-NWs in the air was obtained from the optical model applying Bruggeman effective medium approach. It was determined that ZnO-NWs effective layer consists of 30 % ZnO and 70 % void. Reflectance difference before and after ZnO-NWs modification with BSA was 6.6 times higher than in the case of plain ZnO layer. The Δ kinetics of covalent BSA immobilization on APTES/ZnO-NWs/ZnO/glass substrate contains two phases. Evaluation of diffusion coefficient for BSA into PBS filled APTES/ZnO-NWs/ZnO/ITO/glass was performed using numerical calculation, and the obtained diffusion coefficient was 2.4·10-17 m2 /s. Simulation of BSA immobilization on flat ZnO layer and on ZnO-NWs modified surface showed that 13 times higher sensitivity for wavelength to refractive index change was observed for the substrate with ZnO-NWs.