Delamination of montmorillonite in serum-A new approach to obtaining clay-based biofunctional hybrid materials

Adsorption of proteins on the surface of smectites (e.g. montmorillonite-MMT) is a well established method for selective removal of some proteins from mucosal fluids. In this paper we report on an investigation of structural aspects of the adsorption of proteins occurring in normal human serum (NHS) on montmorillonites. Extensive structural studies, involving X-ray scattering (WAXS and SAXS) and electron microscopy (TEM) techniques, revealed that adsorption of proteins from normal human serum (NHS) causes montmorillonite to exfoliate, in a similar manner as in exfoliated polymer-layered silicate nanocomposites. Although the mechanism of exfoliation was not finally explained, the results indicate that it relies on synergistic adsorption of proteins on the surface of the clay. Apart from exfoliated, SAXS and TEM revealed occurrence of intercalated particles with extremely large distance between subsequent platelets (approx. 10-14 nm). As confirmed by tests of bacterial growth kinetics (with six Salmonella strains), after treatment with MMT. the serum loses its bactericidal properties due to removal of lysozyme. On the other hand, preliminary results indicate that adsorption of lysozyme on the clay surface imparts antibacterial properties to the obtained nanohybrids. The results reported in the paper clearly indicate that adsorption of proteins from natural systems can be considered as a facile route of obtaining exfoliated montmorillonite-protein systems. (C) 2009 Elsevier B.V. All rights reserved.