Bioengineering of stainless steel surface by covalent immobilization of enzymes. Physical characterization and interfacial enzymatic activity.

Two hydrolytic enzymes, namely lysozyme and trypsin, were covalently immobilized onto stainless steel surfaces using wet chemistry processes. The immobilization strategy took advantage of the spontaneous physisorption of the polymer poly(ethylene imine) (PEI) onto stainless steel to yield a firmly attached, thin organic layer containing a high density of primary amine functions. Both enzymes were then covalently grafted to the surface via a glutaraldehyde cross-linker. Alternatively, a thicker underlayer of PEI was chemisorbed by cross-linking two PEI layers by glutaraldehyde. The effective presence of both enzymes on the stainless steel surfaces and their relative amount were assessed by immunochemical assays employing specific anti-enzyme antibodies. Eventually, the hydrolytic activity of the immobilized enzymes was evaluated by local enzymatic tests with suitable substrates. This work demonstrates that, although the amount of enzymes did not vary significantly with the underlayer thickness, their hydrolytic activity could be much improved by increasing the distance from the oxide surface and, likely, by favoring their accessibility. Our data suggest that the immobilization of enzymes on solid oxide surfaces is feasible and efficient, and that the enzymes retain catalytic activity. It may thus provide a promising route towards biofilm-resistant materials.