Silica with biomolecules

We showed that these mesoporous silica materials, with variable pore sizes and susceptible surface areas for functionalization, can be utilized as good separation devices and immobilization for biomolecules, where the ones are sequestered and released depending on their size and charge, within the channels. Mesoporous silica with large-pore-size stmctures, are best suited for this purpose, since more molecules can be immobilized and the large porosity of the materials provide better access for the substrates to the immobilized molecules. The mechanism of bimolecular adsorption in the mesopore channels was suggested to be ionic interaction. On the first stage on the way of creation of chemical sensors on the basis of functionalized mesoporous silica materials for selective determination of herbicide in an environment was conducted research of sorption activity number of such materials in relation to 2,4-D. 

The use of silica particles in bioapplications began with the publication by Stober et al. in 1968 on the preparation of monodisperse nanoparticles and microparticles from a silica alkoxide monomer (e.g., tetraethyl orthosilicate or TEOS). Subsequently, in the 1970s, silane modification techniques provided silica surface treatments that eliminated the nonspecific binding potential of raw silica for biomolecules (Regnier and Noel, 1976). Derivatization of silica with hydrophilic, hydroxylic silane compounds thoroughly passivated the surface and made possible the use of both porous and nonporous silica particles in all areas of bioapplications (Schiel et al., 2006). 

Unmodified silica was found to have a low adsorptive capacity with respect to vitamin E. In the case of modified silica the quantity of immobilized biomolecules is significantly increased (Figure 2). The adsorption of vitamin E does not prevent interaction of silica with vitamin C (Figure 3). It was found that the adsorption of vitamin C from ethanol solution, on the surface of modified silica with preadsorbed vitamin E, is thermodynamically favourable (AGads = -31 kJ/mol). 

Functionalising these types of silica with amino groups is important for potential application in both biomolecular separation and immobilisation. In the separation of proteins by techniques such as ion exchange chromatography, amino surface groups are a commonly used functionality. For immobilisation of biomolecules, the surface amino group can be used as a first functional group to which other chemical species can be attached and consequently used to immobilise biomolecules [9],... 

IUPAC classification, mesoporous materials are defined as porous materials with diameters in the range 2-50 nm, which is rather dose to the dimensions of functional biomolecules such as proteins. Therefore, unexplored phenomena and functions could be observed for biomolecules confined in mesopore channels due to their restricted motion and orientation. In this chapter, we briefly introduce recent developments on the immobilization of biomolecules in mesoporous media, where the use of mesoporous silica and mesoporous carbon are mainly discussed. 

In this paper, the bulk material was obtained by impregnation of the silica host with GFP solution and nanosised by sonication, preserving the features of both the biomolecule and the mesoporous structure. An exhaustive physical chemical characterisation of the nanosized materials was performed by structural (X-Ray Diffraction, Transmission Electron Microscopy), volumetric and optical (photoluminescence spectroscopy) techniques. 

S. Santra, P. Zhang, K.M. Wang, R. Tapec, and W.H. Tan, Conjugation of biomolecules with lumino-phore-doped silica nanoparticles for photostable biomarkers. Anal. Chem. 73, 4988-4993 (2001). 

Several enzymes have been immobilized in sol-gel matrices effectively and employed in diverse applications. Urease, catalase, and adenylic acid deaminase were first encapsulated in sol-gel matrices [72], The encapsulated urease and catalase retained partial activity but adenylic acid deaminase completely lost its activity. After three decades considerable attention has been paid again towards the bioencapsulation using sol-gel glasses. Braun et al. [73] successfully encapsulated alkaline phosphatase in silica gel, which retained its activity up to 2 months (30% of initial) with improved thermal stability. Further Shtelzer et al. [58] sequestered trypsin within a binary sol-gel-derived composite using TEOS and PEG. Ellerby et al. [74] entrapped other proteins such as cytochrome c and Mb in TEOS sol-gel. Later several proteins such as Mb [8], hemoglobin (Hb) [56], cyt c [55, 75], bacteriorhodopsin (bR) [76], lactate oxidase [77], alkaline phosphatase (AP) [78], GOD [51], HRP [79], urease [80], superoxide dismutase [8], tyrosinase [81], acetylcholinesterase [82], etc. have been immobilized into different sol-gel matrices. Hitherto some reports have described the various aspects of sol-gel entrapped biomolecules such as conformation [50, 60], dynamics [12, 83], accessibility [46], reaction kinetics [50, 54], activity [7, 84], and stability [1, 80],... 

Template synthesized silica nanotubes (SNTs) provide unique features such as end functionalization to control drug release, inner voids for loading biomolecules, and distinctive inner and outer surfaces that can be differentially functionalized for targeting and biocompatibility.50 A general path to synthesize nanotubes utilizes anisotropic materials as template. They are coated with silica using Si(OR)4 precursors and nanotubes of Si02 are obtained after removal of the template (Figure 1.24). 

The ion-exchangers used in LC consist either of an organic polymer with ionic functional groups, or silica coated with an organic polymer with ionic functional groups. The types of functional groups used are the same as described in Chapter 18. Since IEC can be carried out with an aqueous mobile phase near physiological conditions, it is an important technique in the purification of sensitive biomolecules such as proteins. 

FIGURE 8.16 Representation of a biomolecule nanoencapsulated in the silica network. (Reprinted from M. Kato et al., J. Sep. ScL, 28 1893 (2005). With permission. Copyright Wiley-VCH 2005.)... 

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