Magnetic Fe3O4 nanoparticles (MNPs) owing to the unique properties and advantages of magnetite, therefore, there has strong interest in application of immobilized enzyme. To maintain performance and properties of MNPs and combine with enzyme better, MNPs have to be modified. MNPs were prepared by a modified hydrothermal method. 20 mL of Fe(NO3)3 (0.16 mol/L) solution and 20 mL of FeSO4 (0.1 mol/L) solution were mixed and stirred, then adding ammonium hydroxide (25%) quickly to adjust the pH to 10 (approximately10 mL) at room temperature, followed by at 130℃ for 3 h in high pressure reactor. The black precipitate of magnetite was formed, which were strongly attracted by a permanent magnet and separated by magnetic decantation. The MNPs were alternating washed 3 times with 10 mL of deionized water, 2 times with 10 mL of ethanol and dried at 45℃. In order to prepare silica layers onto MNPs, sol-gel procedure was employed. This method is based on hydrolysis and condensation of tetraethyl orthosilicate (TEOS). The procedure of MNPs coated with SiO2(MNPs@SiO2) was followed: 100mg of MNPs were dispersed in 100 mL of 80% (v/v) ethanol using sonication for 30min, then ammonium hydroxide (25%) were added quickly to adjust the pH to 9-10 (approximately10 mL), followed by 2 mL of TEOS added and stirred for 3 h at room temperature. The MNPs @SiO2nanocomposite were obtained, then the MNPs@SiO2 were alternating washed 3 times with 10 mL of deionized water, 2 times with 10 mL of ethanol and dried at 45℃.The procedure of composite-modified aggregates with green deep eutectic solvents (MNPs @SiO2-DESs) was followed, three kinds of DESs based on choline chloride (ChCl) were synthesized, and DESs were prepared by heating two eutectic mixtures at 100℃ in a water bath with agitation until a homogeneous and colourless liquid was formed.1 mL of DES was dissolved in 3 mL of methanol, and then 10 mg of MNPs @SiO2 were dispersed among them using sonication and stirred for 2 h at room temperature. The MNPs @SiO2-DES were obtained and alternating washed 3 times with 10 mL of deionized water, 2 times with 10 mL of ethanol and dried at 45℃.The particle aggregates as carrier were used for immobilizedα-amylase by method of cross-linking covalently, 10mg of MNPs@SiO2-DES was dispersed in a solution of 2 mL of glutaraldehyde (volume fraction 5%) by sonication and the mixture was stirred for 1 h at room temperature. The activated support was separated and washed 3 times with 10 mL of deionized water for, followed by adding 4mL ofα-amylase (approximately 9 U/mL in 0.1 M sodium phosphate buffer, pH=6.0). The solution was incubated in a water bath at 25℃for 3 h. The enzyme-bound bioconjugate was separated, washed three times with 10 mL of phosphate buffer (pH=6.0), dispersed in 10 mL PBS and stored at 4℃. The structures and physicochemical properties of the aggregates were studied by transmission electron microscope (TEM), scanning electron microscope (SEM), infrared ray (IR), thermal gravity analysis (TGA), physical property measurement system (PPMS), and determination of enzyme activity, respectively. The results of TEM and SEM indicated that the particles aggregates were spherical with irregular surface, which were nanoscale (particle size of MNPs were range from 10 to 20 nm, particle size of Fe3O4@SiO2were around 100nm) and had properties of better dispersity; meanwhile, MNP distributed inside them. The result of magnetic responsiveness as PPMS showed, the saturation magnetization of Fe3O4and Fe3O4@SiO2were 65.42, 42.57 emu/g, respectively, and the saturation magnetization of Fe3O4@SiO2-DESs were decrease; However, it is adequate enough to separate the material from solutions. The surface of particle aggregates owned abundant functional groups and stable structure estimated by IR and TGA, The IR spectrum of Fe3O4@SiO2 and Fe3O4@SiO2-DESs showed that there were big differences, especially the band located at between 3 600 and 3 000 cm-1and the region of 1 000-1 200 cm-1. Because of hydroxyl groups or amino groups affected by hydrogen bonding, the movement of band position and broadening of peak occurred in original (-OH) or (-NH2). In comparison of TGA curves, difference of weight loss between 150℃and 800℃ exhibited the thermal stability and amount of DESs on the surface of Fe3O4@SiO2was DES2 (18.81±1.96)%, DES1 (9.57±1.36)% and DES3(8.87±0.34)%, respectively. Composite-modified aggregates with DES3were more beneficial to combine withα-amylase. As for immobilization ofα-amylase, composite-modified aggregates with DES3 as carrier had better adsorption performance and higher more enzyme activity, too. Composite-modified aggregated with DES3 is more suitable to be utilized in the carrier of immobilizedα-amylase; furthermore, attributed to the convenient magnetic separation, the immobilizedα-amylase could be easily recycled.%磁性 Fe3O4材料应用于固定化酶具有易分离和回收、操作简便等优点。为保持磁性材料优良的性能，更好的与酶结合，需要对磁性Fe3O4纳米颗粒进行修饰。使用低共熔试剂、二氧化硅等材料对制备的超顺磁性Fe3O4颗粒进行表面复合修饰，经修饰后的颗粒用于固定化α-淀粉酶，通过透射电子显微镜分析、扫描电镜分析、红外光谱分析、热重分析、综合物性分析、酶活力测定等手段研究了颗粒的结构组成、理化特性。结果表明，载体颗粒呈球形，粒径均在100 nm以下，表面有不规则物，Fe3O4纳米颗粒较均匀镶嵌于其中，分散性好。磁性Fe3O4纳米颗粒饱和磁化强度为65.42 emu/g，固定化酶后饱和磁化强度仍在21.90 emu/g以上。颗粒表面有丰富的功能基团，且修饰较稳定，其中DES3修饰的复合颗粒酶固载量达145.2μg/(10 mg)，且催化活性最高，是良好固定化酶的载体材料。
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