In this work, alpha-amylase enzyme was covalently immobilized on the surface of silica-coated modified magnetite nanoparticles, for the first time. The synthesis and immobilization process is simple and very fast and consists of the following steps: (1) preparing the magnetic iron oxide nanoparticles using the co-precipitation method, (2) coating NP with silica (SiO2) by sol-gel reaction, (3) preparing the amino-functionalized magnetite NPs by treating silica-coated NPs with 3-aminopropyltriethoxysilane, (4) activating immobilization of alpha-amylase on the activated amino-functionalized magnetite NPs, and (5) covalently immobilization of alpha-amylase on the activated-amino-functionalized magnetite NPs. The synthesis steps and characterizations of NPs were examined by FT-IR, XRD, EDX and TEM. The optimum concentration and time for maximum enzyme activity of the immobilized alpha-amylase are identified to be 150 mu g and 4 h, respectively for the hydrolysis of starch. The immobilized alpha-amylase showed maximal catalytic activity at pH = 6.5 and 45 degrees C. The kinetic studies shows overall enhancement in the performance of the immobilized enzyme with reference to the free enzyme. Similarly, the thermal stability of the enzyme is found to increase after the immobilization. The Immobilized alpha-amylase has also been demonstrated to be capable of being reused for six cycles while retaining similar to 85% of the initial activity. By using a magnetically active support, quick separation of amylase from reaction mixture is enabled. The K-m values were found as 6.27 and 4.77 mM for free and immobilized enzymes, respectively. The V-max values for the free and immobilized enzymes were calculated as 2.44 and 11.58 mu mol/mg min, respectively. (C) 2013 Elsevier B.V. All rights reserved.