The paper presents a method for preparing hybrid magnetic cross-linked enzyme aggregates (M-CLEAs) using carboxyl magnetic nanoparticles (MNP). The magnetic nanoparticle-enzyme complexes induced by electrostatic interaction between carboxyl group of magnetic particle and amino group of enzyme were separated from the solution under magnetic field

and then were cross-linked by glutaraldehyde. The traditional method of M-CLEAs preparation from amino-modified magnetic nanoparticles and the enzyme need the precipitant to prompt the separation of enzyme and magnetic nanoparticle from the solution. The method here proposed does not need the precipitant

thereof the process is greatly simplified. In this paper

the factors of cross-linking time

pH

enzyme concentration and concentration of glutaraldehyde in M-CLEAs preparation process were studied

and then the enzymatic properties of M-CLEAs were also investigated in detail. The results showed that the optimum conditions were as follows: enzyme concentration of 1 mg·ml-1

magnetic fluid concentration of 10 mg·ml-1

glutaraldehyde concentration of 0.25% and crosslinking reaction at pH 6.0 for 6 h. The final enzyme loading reached 80 mg·g-1 and the activity of M-CLEAs was 50 U·mg-1. The pH stability

thermostability and storage stability of the immobilized enzyme improved significantly

and M-CLEAs still remained nearly 60% of activity after 10 cycles.