Biological applications of zinc imidazole framework through protein encapsulation

Appl Nanosci DOI 10.1007/s13204-015-0511-x ORIGINAL ARTICLE Biological applications of zinc imidazole framework through protein encapsulation Pawan Kumar1 • Vasudha Bansal1 • A. K. Paul2 • Lalit M. Bharadwaj3 • Akash Deep2 • Ki-Hyun Kim1 Received: 27 July 2014 / Accepted: 16 November 2015 Ó The Author(s) 2015. This article is published with open access at Springerlink.com Abstract The robustness of biomolecules is always a significant challenge in the application of biostorage in biotechnology or pharmaceutical research. To learn more about biostorage in porous materials, we investigated the feasibility of using zeolite imidazolate framework (ZIF-8) with respect to protein encapsulation. Here, bovine serum albumin (BSA) was selected as a model protein for encapsulation with the synthesis of ZIF-8 using water as a media. ZIF-8 exhibited excellent protein adsorption capacity through successive adsorption of free BSA with the formation of hollow crystals. The loading of protein in ZIF-8 crystals is affected by the molecular weight due to diffusion-limited permeation inside the crystals and also by the affinity of the protein to the pendent group on the ZIF-8 surface. The polar nature of BSA not only supported adsorption on the solid surface, but also enhanced the affinity of crystal spheres through weak coordination interactions with the ZIF-8 framework. The novel approach tested in this study was therefore successful in achieving protein encapsulation with porous, biocompatible, and decomposable microcrystalline ZIF-8. The presence of both BSA and FITC–BSA in ZIF-8 was confirmed Electronic supplementary material The online version of this article (doi:10.1007/s13204-015-0511-x) contains supplementary material, which is available to authorized users. & Pawan Kumar 1 Department of Civil and Environmental Engineering, Hanyang University, 222 Wangsimni-Ro, Seoul 133-791, Republic of Korea 2 Central Scientific Instruments Organisation (CSIR-CSIO), Sector 30 C, Chandigarh 160030, India 3 Amity Institute of Nanotechnology, Noida, India consistently by spectroscopy as well as optical and electron microscopy. Keywords Zeolitic imidazolate framework (ZIF-8)
Proteins
BSA
Successive adsorption Introduction Proteins are natural and fundamental bio-functional units consisting of one or more chains of amino acids. They play many biological roles, such as catalysts with enhanced reactivity, selectivity, and specificity under mild conditions. If immobilized on a solid and porous surface, proteins can exhibit prolonged biological functioning (Pinto Reis et al. 2006; Gao et al. 2009; Lee et al. 2010; Worsdoorfer et al. 2012). In this regard, a great deal of attention has been drawn to the porous materials used as support due to their potential for interaction with proteins (Pinto Reis et al. 2006; Gao et al. 2009; Lee et al. 2010; Worsdoorfer et al. 2012). Nonetheless, development of these materials faces major challenges by insufficient stability of encapsulated proteins, e.g., incomplete release or initial burst release. It is widely perceived that chemical and mechanical stress are produced during the process of microencapsulation and that a longer duration of storage can increase damaging effects on the conformational and biological integrity of the protein (Yeo and Park 2004). Moreover, application of protein encapsulation for sensing also has challenges and difficulties due to reductions in (a) sensitivity, (b) activity, (c) operational stability, (d) recovery, and (e) reusability under certain experimental conditions (Such et al. 2011; Danhier et al. 2012). Consequently, there is a need for more research on the build-up of multi functionality platforms for proteins to overcome these major limitations. 123 Appl Nanosci The incorporation of biomolecules or nanomaterials on metal organic frameworks (MOFs) has attracted a great deal of interest because of their potential for clinical, health, and environmental applications due to the novel chemical, physical, and optical properties of those materials (Czaja et al. 2009; Chen et al. 2010; Lohe et al. 2011; Danhier et al. 2012; Liu 2012). MOFs are the structural analogs of zeolites, but are different in terms of their stability, selectivity, porosity, and especially feasibility of building a crystal structure. Development of MOFs has thus been remarkably achieved in various fields of study including catalysis, nonlinear optics, separation, magnetism, fluorescence, gas storage, ion exchange, and others (Allendorf et al. 2009; Buso et al. 2011; Sugikawa et al. 2011; Tsuruoka et al. 2011). Recently, the synthesis and design of zeolitic imidazolate framework (ZIF-8) have been favored following the recognition of its interatomic potential, topologies, framework architectures, large cavities (11.6 Å at window size of 3.4 Å), and chemical/thermal stability (Watson et al. 2002; Park et al. 2006; Phan et al. 2010; McKinlay et al. 2010; Springuel-Huet et al. 2013). This large window size of ZIF-8 allows greater flexibility to accommodate large guest molecules in the support material. In this respect, much of the current knowledge is based on the pioneering work of Lu et al. (2012), who demonstrated the encapsulation of nanoparticles in ZIF-8 (as molecular sieving) with the same functional characteristics as those of the isolated nanoparticles (Lu et al. 2012). Here, we present the first report of a protein encapsulation strategy in ZIF-8, to the best of our knowledge. To this end, the incorporation (or immobilization) of biomolecules (or protein) was achieved within Zeolitic imidazolate Fig. 1 Protein (BSA) incorporation in ZIF-8 scheme: SEM image, a ZIF-8 blank crystal and b ZIF–BSA composite. Bovine serum albumin (BSA) of size 2–4 nm with globular shape was well dispersed in ZIF-8 crystals due to assembly of zinc ions with imidazolate ligand 123 framework material (ZIF-8). This fundamental strategy was used for the development of the synthesis of ZIF-8 in an aqueous medium in the presence of BSA, a model protein. Experimental Materials All of the solvents and reagents, including zinc nitrate hexahydrate (Merck), methyl imidazolate (Merck), trimethyl ethyl amine (TEA), bovine serum albumin, and FITC–BSA (Sigma-Aldrich), were purchased as analytical grade and used as received. The UV–Vis spectroscopy (Varian Cary 500) was carried out in the range of 200–3300 nm. The synthesis and confirmation of crystal formation was done using X-ray diffraction (Shimadzu, 6000 diffractometer). Topological studies were performed using a confocal microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM). The conjugate formation was confirmed by FTIR spectroscopy (Thermo-2400). ZIF-8 synthesis and encapsulation of BSA To prepare ZIF-8 in aqueous medium, we followed the synthesis procedure of Watson et al. (2002), as shown in Fig. 1a, b (Watson et al. 2002; Kida et al. 2013). The same procedure described by (...truncated)