Biofunctionalization of silica microspheres for protein separation

Imidazole-octyl mixed-mode stationary phase based on macroporous silica for the purification of ovomucoid and ovotransferrin

A process-simplified hard template approach was established to synthesize the monodisperse macroporous silica microspheres with homogeneous structures by twice alkali-thermal treatment and calcination routes. Porous vinyl-functionalized polysesquioxane microspheres (V-PMSQ) were synthesized through a hydrolyzation-polycondensation method and used as templates. The template particles with large aperture and high pore volume were obtained by adjusting the pH value and reaction time of the twice alkali-thermal reaction. After calcination, monodisperse silica microspheres with an average pore size of 30 nm, homogeneous pore structures, and narrow particle size distribution were fabricated, which can be directly used as chromatographic matrices without classification. After that, a new reversed-phase/strong anion-exchange (RP/SAX) mixed-mode stationary phase Sil-S-VOIM was prepared by bonding the 1-vinyl-3-octyl-imidazole ligands to the above silica microspheres through a "thiol-ene" click reaction. The performance of the Sil-S-VOIM column was evaluated by one acidic protein (transferrin) and two basic proteins (lysozyme, α-chymotrypsin) and compared to a single imidazole-modified Sil-S-VIM column and an octyl-modified Sil-C8 column, respectively. Due to the synergistic effect of electrostatic repulsion and hydrophobic interactions, baseline separations of the above proteins were observed only on the Sil-S-VOIM column, with resolutions of 2.55 and 2.01 between lysozyme and transferrin, and between transferrin and α-chymotrypsin, respectively, indicating good selectivity and separation ability compared with single-mode stationary phases. It was applied to the isolation of egg white samples with peaks identified by SDS-PAGE and MALDI-TOF-MS. The results showed that the selective retention and isolation of ovomucoid and ovotransferrin were successfully achieved, with yields of 78.8% and 67.2%, respectively. The protocol described in this work is simpler, faster, and has higher protein recovery. Overall, this new mixed-mode stationary phase provided a promising potential for the separation and determination of intact proteins.

Facile synthesis of peanut-like Sn-doped silica nano-adsorbent for affinity separation of proteins

A peanut-like hollow silica (denoted as p-l-hSiO₂) adsorbent is prepared in a facile method, which is composed of several silica nanospheres and has an average diameter of 22 nm, with thickness of 5 nm. Its Brunauer–Emmett–Teller (BET) surface area, pore volume and pore size are 258.9 m² g⁻¹, 1.56 cm³ g⁻¹ and 3.9 nm, respectively. Then the afforded p-l-hSiO₂/GSH adsorbent is applied to purify glutathione S-transferases-tagged (denoted as GST-tagged) proteins. It is found that the p-l-hSiO₂ adsorbent exhibits a specific adsorption, a high binding capacity (6.80 mg g⁻¹), good recycling performance and high recovery (90.1%) to the target proteins, showing promising potential for the affinity separation of GST-tagged proteins.

Peanut-like Sn-doped hollow silica adsorbent is prepared in a facile method, which exhibits a specific adsorption, a high binding capacity , good recycle performance and high recovery to the GST-tagged proteins.

Silica Microspheres-in-Pores Composite Monoliths with Fluorescence and Potential for Water Remediation

Water pollution is a severe worldwide issue. Constructing advanced porous composite materials has been an efficient route to water remediation via adsorption. In this study, a unique microspheres-in-pores monolithic structure was fabricated. An emulsion-templated polymer monolith was first prepared and silica microspheres were subsequently formed in the porous polymer. A silica precursor was modified with a fluorescent dye and co-condensed with other precursors to fabricate porous composites with fluorescent properties, which were enhanced by the presence of Ag nanoparticles in the polymer matrix. This unique material showed good promise in water remediation by removing organic dyes and heavy metal ions from wastewater via a flowing filter or monolithic column separation.

Selective binding, magnetic separation and purification of histidine-tagged protein using biopolymer magnetic core-shell nanoparticles

In previous studies, we synthesized the magnetic core-shell structured Fe₃O₄/PMG/IDA-Ni²⁺ nanoparticles. The Ni²⁺ on the surface of nanoparticles provides abundant docking sites for histidine, and the composite nanoparticles showed potential applications in the separation and purification of histidine-tagged (His-tagged) proteins. Meanwhile, the presence of the superparamagnetic core (Fe₃O₄) in the nanoparticles allows them to be quickly separated and purified by an external magnetic field. Herein, the ability of magnetic nanoparticles to purify His-tagged human superoxide dismutase 1 (hSOD1) was verified. SDS-PAGE and activity data showed His-tagged hSOD1 specifically bound to Fe₃O₄/PMG/IDA-Ni²⁺, and there was no significant competition for binding between final and three intermediate products. The binding capacity of nanoparticles can reach to 62.0 mg/g (dry weight of hSOD1/nanoparticles). The nanoparticle-bound hSOD1 exhibited better thermal and storage stability compared to free hSOD1. Furthermore, the purification efficiency of the magnetic nanoparticles in the separation and purification of His-tagged proteins was comparable to the other two commercial materials (High Affinity Ni-NTA Resin, HisPur Ni-NTA Magnetic Beads). Finally, the magnetic nanoparticles can be reused in the binding of His-tagged protein for multiple times. In conclusion, the nanoparticles are ready to be applied in the separation and purification of His-tagged protein.

Tetra-nickel substituted polyoxotungsate as an efficient sorbent for the isolation of His6-tagged proteins from cell lysate

By virtue of the flexible structure of polyoxometalates, Ni²⁺ is encapsulated into trivacant lacunary tungstophosphate ligands by the form of [Ni₄] cluster to offer a tetra-nickel substituted polyoxotungsate K₆Na₄[Ni₄(H₂O)₂(PW₉O₃₄)₂] (Ni₄P₂). The Ni₄P₂ is then immobilized onto the surface of SiO₂ nanoparticles by self-assembly under electrostatic interactions to give the product of Ni₄P₂@SiO₂ composites. Due to the specific affinity between substituted Ni²⁺ in the polyoxotungsate and the histidine residues of protein, Ni₄P₂@SiO₂ composites exhibit highly adsorption selectivity towards histidine protein. This Ni₄P₂@SiO₂ composite is of high stability, and SDS-PAGE assay indicates that it can be used repeatedly as an efficient sorbent for the isolation of His6-tagged proteins from cell lysate with improved performance when compared with commercial NTA-Ni²⁺ column.

Preparation of Monodisperse Porous Silica Particles Using Poly(Glycidyl Methacrylate) Microspheres as a Template

Monodisperse macroporous poly(glycidyl methacrylate) (PGMA) microspheres were used as a template for preparing porous silica particles. The starting polymer microspheres that were 9.3 μm in size were synthesized by multistep swelling polymerization using a modified Ugelstad technique. Subsequently, silica (SiO2) was deposited on the surface and inside the PGMA microspheres to produce poly(glycidyl methacrylate)-silica hybrid particles (PGMA-SiO2). Upon calcination of the PGMA-SiO2 microspheres, porous silica particles were formed. The morphology, particle size, polydispersity and inner structure of the silica microspheres were investigated by scanning and transmission electron microscopy. Thermogravimetric analysis and dynamic adsorption of nitrogen determined the amount of silica formed and its specific surface area. Compared with the starting PGMA microspheres, the size of the porous silica particles decreased by up to 30 %. These porous silica microspheres are promising for chromatography and biomedical applications.

Synthesis of petal-like ferric oxide/cysteine architectures and their application in affinity separation of proteins

Petal-like ferric oxide/cysteine (FeOOH/Cys) architectures were prepared through a solvothermal route, which possessed high thiol group density. These thiol groups as binding sites can chelate Ni(2+) ions, which can be further used to enrich and separate his-tagged proteins directly from the mixture of lysed cells without sample pretreatment. These results show that the FeOOH/Cys architectures with immobilized Ni(2+) ions present negligible nonspecific protein adsorption and high protein adsorption capacity, with the saturation capacity being 88mg/g, which are especially suitable for purification of his-tagged proteins.