Sol-gel encapsulation methods

Dave, B.C., Dunn, B., Valentine, J.S. and Zink, J.I. (1994) Sol-gel encapsulation methods for biosensors. Analytical Chemistry, 66, 1120A-1127A. 

B.C. Dave, B. Dunn, J.S. Valentine, and J.I. Zink, Sol-gel encapsulation methods for biosensors. Anal. Chem. 66, 1120A-1126A (1994). 

Dave B C, Duim B, Selverstone Valentine J, Zink J I (1994) Sol-gel encapsulation methods for Biosensors. Anal Chem 66 1120A-1127A. 

Dave, B.C., et al., Sol-Gel Encapsulation Methods for Biosensors. Analytical Chemistry, 1994. 66 p. 1120A- 1127A. 

J. Yu, S. Liu, and H.X. Ju, Mediator-free phenol sensor based on titania sol-gel encapsulation matrix for immobilization of tyrosinase by a vapor deposition method. Biosens. Bioelectron. 19, 509-514 (2003). 

Entrapment in polymeric matrices is a variation of noncovalent attachment where the support is instead generated in the presence of the enzyme. A particularly popular entrapment technique is sol-gel encapsulation, where the enzyme is trapped within an Si02 matrix formed by acid- or base-catalysed hydrolysis of tetraalkoxysilanes in the presence of enzyme. ° The technique can be tuned to provide the appropriate microenvironment for each enzyme in much the same way as can be done with other immobihzation methods. ... 

In a previous work, Tardioli et al. [9] have immobilized CGTase from Thermoanaerobacter sp. by covalent attachment into glyoxy 1-agarose particles and obtained an activity recovery of about 32%, that is, five times the highest values obtained in this work (6.94% with sol-gel encapsulation). It is thought that with the latter method, in addition to the causes listed above for immobilized enzyme activity loss, the immobilization conditions and reagents used by the sol-gel method contribute to enzyme deactivation. 

One merit of special attention in this chapter is the fact that sol-gel synthesis offers a convenient method for hosting chemical reactions, a process which is not possible using other synthesis techniques. Typically, in sol-gel encapsulation, silica nanoparticles surround the captive molecules during gel formation. In principle, the sol-gel process can be considered as a phase separation by sol-reactions, sol-gelation and finally, removal of the solvent resulting in a ceramic material Depending on the preparation, dense oxide particles or polymeric clusters will be obtained [16]. 

Confining enzymes within the lattices of polymerized gels is another method for immobifization. Such occlusion does not lead to any bond formation between the enzyme and the polymer matrix thus, there is no disruption of the protein molecules. Such biocatalysts are robust and are easy to recover however, appHcation of sol-gel encapsulation has been more related to chemical analysis than bioprocesses. 

In this chapter, we overview some of the more advanced and promising protein immobilization technologies that have become available in the last decade, especially the fabrication of organized thin film architectures, sol-gel encapsulation, crosslinked crystals, and protein-polymer composites. The current status and applicability of these methods in the catalyst, sensor, and diagnostics arenas, as well as prospective applications and future developments are discussed. 

Stability of the chromophore was observed usiag uv-vis spectroscopy, the authors conclude that this sol—gel method of chromophore encapsulation does not provide any real thermal or oxidative protection in either the covalendy or noncovalently bonded state. 

Very few examples have been described for the non-covalent immobilization of chiral porphyrin complexes (Fig. 26). In the first case, the porphyrin-dichlororutheninm complex was encapsulated in silica, which was prepared around the complex by a sol-gel method [78], in an attempt to prevent deactivation observed in solution in the epoxidation of different alkenes with 2,6-dichloropyridine N-oxide. In fact, the heterogeneous catalyst is much more active, with TON up to 10 800 in the case of styrene compared to a maximum of 2190 in solution. Enantioselectivities were about the same imder both sets of conditions, with values aroimd 70% ee. 

---