Immobilization of bio-macromolecules onto membranes via an adsorbed nanolayer: An insight into the mechanism

We have examined the mechanism of bio-macromolecule immobilization onto membranes via an intermediate adsorbed nanolayer. Unlike the formation of polyelectrolyte complex membranes where two charged polyelectrolytes complex each other in a single shot, the bioactive macromolecule immobilization onto membranes involves first the sorption of a polyelectrolyte nanolayer. This results in a firmly adsorbed hydrophilic layer with an overall charge inversed from that of the membrane surface, onto which bio-macromolecules can be adsorbed by multi-point electrostatic interactions. The formation mechanism of the materials is discussed on the basis of thermodynamical and kinetical analyses. The process of polyelectrolyte sorption would be kinetically blocked in a metastable state due to a large increase in the activation energy at a large extent of chain–surface ion-pairing. A variety of situations is expected according to the conditions of sorption of the successive layers. The implications of this for a better bio-macromolecule immobilization for different applications are discussed.