Synthesis of Core/Shell Colloidal Magnetic Zeolite Microspheres for the Immobilization of Trypsin
Synthesis of Core/Shell Colloidal Magnetic Zeolite Microspheres for the Immobilization of Trypsin
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固定化胰蛋白酶的核/壳胶体磁性沸石微球的合成
DOI：
10.1002/adma.200801766
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发表时间：
2009-04-06
影响因子：
29.4
通讯作者：
Zhao, Dongyuan
中科院分区：
文献类型：
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作者：
Deng, Yonghui;Deng, Chunhui;Zhao, Dongyuan
具有可控结构、形貌和功能的胶体粒子由于其在柱填充基底、光子晶体、药物输送、化学传感器、催化载体和生物大分子分离等方面的潜在应用而受到广泛关注。特别是胶体磁性微球，由于其易于功能化的表面和磁响应性的完美结合，作为杂化材料长期以来一直受到极大的关注。这种组合赋予它们在微型设备中使用的巨大潜力，其中需要通过磁场进行简单的操作，分离和位点特异性靶向。磁性微球的合成方法很多，包括用有机聚合物（如聚苯乙烯）包裹磁性颗粒，以及用溶胶-凝胶法在磁性颗粒表面包覆无机二氧化硅等。磁性微球在细胞分选、生物分子分离等领域也有着广泛的应用前景，近年来，磁性微球的性能研究一直是磁性微球研究的热点.这些包括努力改善它们的磁场响应性，以便实现有效的操纵，以及努力引入额外的功能，以便定制它们的物理化学性质（例如，高表面积和官能团）以实现亲和结合或特异性缀合。在这方面，我们已经合成了亚微米大小的磁性微球，通过改性的溶胶-凝胶方法用二氧化硅涂覆磁铁矿颗粒，这些微球被证明是有用的富集低丰度肽。Park等人基于粒子间的异质聚结策略制备了磁性氧化铁/Au微球，并将其用于生物测定。Kim等人报道了通过用介孔二氧化硅同时封装磁铁矿纳米颗粒和CdSe/ZnS量子点来生产磁性荧光多孔微球。Shi及其同事合成了具有无序介孔二氧化硅壳的磁性微球。最近，报道了使用涉及表面活性剂的溶胶-凝胶合成，具有垂直排列的介孔二氧化硅壳的高磁化、磁性、介孔二氧化硅微球。这些微球已被用于有效地去除水中的微囊藻毒素。微孔沸石是一类重要的具有开放骨架铝硅酸盐结构的无机材料，在气体分离、石油化工催化等工业过程中有着广泛的应用。沸石颗粒由于其低毒性、良好的性能、用于接枝或附着的官能团以及高分散性，已被证明是各种应用中的良好生物材料，例如在微流控系统中的微反应器中的胰蛋白酶的固定化以及在蛋白质鉴定中的低丰度肽的高效富集。然而，与有序介孔硅酸盐（其合成涉及在低温下表面模板溶胶-凝胶过程的自组装，例如，室温），沸石通常使用高温水热法合成。因此，核/壳沸石微球的合成仍然是一个巨大的挑战，因为难以控制沸石晶体在磁铁矿颗粒上的生长。在这篇文章中，我们报道了一种新的方法来合成核/壳结构的磁性沸石微球（MZMs）具有均匀的可变直径（从约100微米）。600 nm至1 mm）。该方法结合了溶胶-凝胶合成的沸石晶种涂层和气相传输（VPT）生长的沸石晶体壳。胶体MZM，由磁铁矿核心组成（约。400 nm直径）和沸石壳（约. 180 nm厚），具有明确的核/壳结构和48.5emug-1（emu：电磁单位）的高磁化强度，并在水中表现出良好的分散性。此外，这些微球显示出很强的亲和性，胰蛋白酶与高吸附容量（62 mgmg）。使用胰蛋白酶固定化MZMs（T-MZMs），在微波照射的辅助下，仅需15秒即可实现高效蛋白质消化，比溶液中的消化快得多。此外，T-MZMs可以通过简单的磁分离方便地回收，并重复使用至少7次，而消化效率没有任何可见的降低。核/壳MZM的合成程序由三个主要步骤组成，如方案1所示。首先，通过溶胶-凝胶法在Fe_3O_4颗粒表面包覆一层SiO_2，制备了Fe_3O_4/SiO_2微球。二氧化硅层防止水热过程中的侵蚀，并用作沸石晶体生长的二氧化硅源。其次，为了使带负电荷的沸石晶种存款在微球表面，用阳离子改性剂聚二烯丙基二甲基氯化铵（PDDA）对Fe_3O_4/SiO_2微球表面进行改性，然后通过库仑作用将沸石晶种纳米粒子（silicalite-1）吸附在微球表面。第三，微球经受
Colloidal particles with controlled structures, morphologies, and functionalities have attracted much attention because of their potential application in column-packing substrates, photonic crystals, drug delivery, chemical sensors, catalysis carriers, and separation of biomacromolecules. In particular, colloidal magnetic microspheres have long been of great interest as hybrid materials, because of their perfect combination of easily functionalizable surfaces and magnetic responsiveness. This combination endows them with great potential for use in miniature devices, where easy manipulation, separation, and site-specific targeting via a magnetic field are desired. A variety of approaches have been explored to synthesize magnetic microspheres, including encapsulation ofmagnetite particles by organic polymers, such as polystyrene, and coating magnetic particles with inorganic silica via sol-gel processes. Possible applications ofmagneticmicrospheres have also been explored infields such as cell sorting, separation of biomolecules, and so on. Recently, great efforts have been focused on enhancing the performance of magnetic microspheres. These include efforts to improve their magnetic-field responsiveness, so as to achieve effective manipulation, and efforts to introduce additional functionalities, in order to tailor their physicochemical properties (e.g., high surface area and functional groups) to achieve affinity binding or specific conjugation. In this regard, we have synthesized submicrometer-sized magnetic microspheres by coating magnetite particles with silica through a modified sol-gel approach; these microspheres proved to be useful in the enrichment of low-abundance peptides. Based on the heterointerparticle coalescence strategy, Park et al. prepared magnetic iron-oxide/Au microspheres, and used them in bioassays. Kim et al. reported on the production of magnetic fluorescent porous microspheres by simultaneously encapsulating magnetite nanoparticles and CdSe/ZnS quantum dots with mesoporous silica. Shi and coworkers synthesized magnetic microspheres with disordered mesoporous silica shells. More recently, using a sol-gel synthesis that involved a surfactant, high-magnetization, magnetic, mesoporous, silica microspheres with perpendicularly aligned mesoporous silica shells were reported. These microspheres have been used for the efficient removal of microcystins in water. Microporous zeolites are important inorganic materials with open-framework aluminosilicate structures, and have been extensively used in industrial processes such as gas separation and petrochemical-based catalysis. Zeolite particles, because of their low-toxicity, good capability, functional groups for grafting or attachment, and high dispersability, have been demonstrated to be good biomaterials in various applications, such as in the immobilization of trypsin for microreactors in microfluidic systems and for the highly efficient enrichment of low-abundance peptides in protein identification. However, unlike ordered mesoporous silicates (whose synthesis involves self-assembly of a surfactant-templating sol-gel process at low temperatures, e.g., room temperature), zeolites are usually synthesized using high-temperature hydrothermal processes. As a result, the synthesis of core/shell zeolite microspheres remains a great challenge, because of the difficulty in controlling the growth of zeolite crystals on the magnetite particles. In this communication, we report a novel approach to synthesizing core/shell-structured magnetic zeolite microspheres (MZMs) with uniform variable diameters (from ca. 600 nm to 1mm). The approach combines sol-gel synthesis of a zeolite seed coating and vapor-phase transport (VPT) for growing the zeolite crystal shells. The colloidal MZMs, which consist of a magnetite core (ca. 400 nm in diameter) and a zeolite shell (ca. 180 nm thick), have a well-defined core/shell structure and a high magnetization of 48.5 emug 1 (emu: electromagnetic units), and exhibit good dispersability in water. Moreover, these microspheres show a strong affinity to trypsin with a high adsorption capacity (62mgmg ). Using trypsin-immobilized MZMs (T-MZMs), highly efficient protein digestion is achieved, with the assistance of microwave irradiation, in only 15 s, which is much faster than digestion in solution. Moreover, the T-MZMs can be conveniently recovered by simple magnetic separation, and reused at least seven times without any visible reduction in digestion efficiency. The synthesis procedure for the core/shell MZMs consists of three main steps, as shown in Scheme 1. First, Fe3O4/SiO2 microspheres are synthesized by coating Fe3O4 particles with a layer of silica via a sol-gel process. The silica layer prevents erosion during the hydrothermal process, and functions as the silica source for the growth of the zeolite crystals. Second, in order to deposit the negatively charged zeolitic seeds on the silica surfaces of the microspheres, a cationic polyelectrolyte, poly (diallydimethylammonium chloride) (PDDA), was used tomodify the surfaces of the Fe3O4/SiO2 microspheres; the zeolite seed nanoparticles (silicalite-1) were then adsorbed on the surfaces by Coulomb interaction. Third, the microspheres were subject to