Optical sensing of the initial stages in the growth and development of fibrin clot

Thrombus formation is a surface phenomenon which is always initiated upon a surface. It makes optical surface sensing systems very reasonable and promising tools for its monitoring and study. We evaluated the feasibility to follow the enzymatic conversion of surface-bound fibrinogen by thrombin to fibrin monomer and possible complex formation between surface-bound fibrin monomer and fibrinogen in solution using a surface plasmon resonance (SPR) sensor. For the investigations of optical properties of immobilised molecular layers, the Kretschmann geometry of the attenuated total reflection (ATR) method was utilised. Density of fibrinogen bound to the surface depended on the concentration of fibrinogen in solution during the adsorption process. A fibrinogen monolayer was always formed. Fibrinogen in solution did not bind to surface-bound fibrinogen. Bound fibrinogen converted by thrombin to fibrin monomer interacted (rather slowly) with fibrinogen in solution. The rate of adsorption depended upon immobilised fibrin monomer density, fibrinogen concentration in solution, and on the presence of calcium ions. At low fibrin monomer density, the second layer was formed that contained about the same amount of protein as the first layer, at higher fibrin monomer concentration less than one molecule of fibrinogen per molecule of fibrin monomer was captured.