Understanding the interactions between proteins and surfaces (nanoparticles or films) is crucial for the fabrication and improvement of biomedical devices in direct contact with human blood. The aim of this work is the study of the interaction of fibrinogen (Fib) with zinc oxide nanoparticles. The nanoparticles were either synthesized chemically or were commercially available, having different size. Zinc oxide nanoparticles are known for their antibacterial properties, and Fib adsorption is studied in view of combining the antibacterial and desirable clotting behavior of a single material. The thermal properties of the Fib solution were studied by Micro-Differential Scanning Calorimetry. For the consideration of the compositional and structural properties of the nanoparticles, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy were employed, respectively. Through the changes of the thermal properties of Fib upon adsorption that were observed by microDSC, the mechanisms of the protein adsorption were revealed. It seems that electrostatic (for the D and E domains) and hydrophobic interactions (for the aC chains) were responsible for the adsorption and the protein structural changes caused by it. The discrepancy between the Fib adsorption percentages on homemade and commercially available zinc oxide nanoparticles can be attributed to their different size. (C) 2013 Elsevier Inc. All rights reserved.