Bio-catalysis has been used for several decades in the food, agricultural and also paper industry. Using enzymes rather than conventional chemical transformations offer many advantages in terms of specificity and selectivity. Moreover, this method requires fewer steps and allows higher yields.

The use of enzymes for industrial processes has greatly increased, therefore different methods have been proposed to enhance both enzyme stability and enzyme bio-activity.

It is well known that the use of immobilized systems is really efficient to optimize stability and bio-activity of enzymes. Binding of enzymes to membrane could be used, but the surface area available for an efficient bio-transformation is not very large. Binding of proteins to "classical polystyrene microspheres" is quite easy and largely used for diagnostic, biotech and life science applications. Proteins could be bound to plain microspheres using the passive adsorption method, or to Functionalized Microspheres (i.e. with COOH, NH2, or OH groups) using the covalent coupling method.

With small microspheres (<1µm), the surface area is very large, but in fact, if the microspheres are too small, their recovery is very difficult and they cannot be easily re-used. With large microspheres (>2µm), their recovery is easier but surface area is insufficient.

Another interesting option is the possible use of super-paramagnetic microspheres for bio-catalysis. For many years, magnetic microspheres have been widely used in diagnostic, biotech and life science fields. Binding of proteins, especially antibody or streptavidin, to magnetic microspheres is now very common and offer several advantages:

• Magnetic microspheres could be very easily retained in the reaction system by a magnetic field.
• Recovery is much easier than conventional methods.
• Magnetic microspheres can be re-used and offer an economical tool in Bio-Processing.