Fibrinogen conjugated gold nanoparticles (fibrinogen-Au) and thrombin conjugated silver nanoparticles (thrombin-Ag) were synthesized by heating (90 °C) the proteins (50 μg protein/ml) with 1 mM AgNO3 or AuCl3. The resultant particles were harvested and examined by flow cytometry, scanning electron microscopy (SEM), transmission emission microscopy (TEM), optical microscopy and dynamic light scattering. SEM and TEM images revealed that the fibrinogen-Au and thrombin-Ag particles interacted. The emergent bio-nanoconjugate population could be controlled by addition of thrombin-Ag. The method may be exploited in parametrizing coagulation factors and other clinically important protein-protein interactions. © 2007 Federation of European Biochemical Societies.