Molecular imaging of fibrinogen by scanning probe microscopy for studying contact activation

The irreversible conversion of the plasma protein fibrinogen to fibrin is an important step within the coagulation process. Contact activation may be stimulated by an electron transfer from the fibrinogen molecule to an alloplastic material. Structure and electronic properties of fibrinogen and material are therefore determining the hemocompatibility. Scanning Probe Microscopy (SPM) is extremely useful for studying these processes. Atomic Force Microscopy allows a structural analysis of biological objects and solid surfaces on nanometer scale under air and even in electrolytes. Scanning Tunneling Microscopy allows a spatially resolved analysis of the electronic properties. In the presented study the interdependence between hemocompatibility and electronic properties of semiconducting materials was analyzed by molecular imaging of fibrinogen with SPM-methods. The structure of fibrinogen was investigated at a molecular scale. Stable imaging was possible under air and in electrolytes. Only on silicon, the material with the smallest band gap regarded, fibrin strands and networks were imaged. On silicon even a time resolved analysis was possible showing the development of fibrin strands in vitro. On the materials with greater band gaps only single molecules and small clusters of fibrinogen were observable. This correlation between electronic properties and contact activation has to be regarded for the development of hemocompatible surface coatings.