Hydrogel entrap enzymes

Heo J. and Crooks R. M., Microfluidic biosensor based on an array of hydrogel-entrapped enzymes, Anal. Chem., 77(21), 6843-6851, 2005. 

Heo, J., Thomas, K.J., Seong, G.H., Crooks, R.M., A microfluidic bioreactor based on hydrogel-entrapped E. coli Cell viability, lysis, and intracellular enzyme reactions. Anal. Chem. 2003, 75, 22-26. 

The versatility of water-soluble polyphosphazenes is in the variations in the structures that can be prepared. Structures with a low glass-transition temperature backbone can be modified with a variety of versatile side units. These may find use in solid polymeric ionic conductors, as a means to entrap and immobilize enzymes with retention of enzymic activity, and in biological functions as hydrogels with the capability of exhibiting biocompatibility and... 

Escherichia coli cells (BL21) were entrapped in hydrogel micropatches. The cells were found to remain viable in the patches. Furthermore, diffusion of small molecules through the polymer (with 1-10 nm pores) to the cells allows cell reactions to be studied. For example, the fluorescent dye BCECF-AM diffused to the cells and the dye was converted to BCECF by intracellular enzymes present only in live cells [1053]. 

Immobilization of nanoparticles and enzymes onto electrode surfaces using various entrapment chemistries, that is, sol-gels, layered polyions, and hydrogels, has allowed for greater functionality and improved stability. Crumbliss and coworkers demonstrated the direct electron transfer between the redox center of HRP by evaporation... 

For the repeated use of enzymes in such an analytical device, numerous techniques for enzyme immobilization including entrapment in hydrogels (membrane... 

Veronese, F.M. Mammucari, C. Schiavon, F. Schiavon, O. Lora, S. Secundo, F. Chilin, A. Guiotto, A. Pegylated enzyme entrapped in poly(vinyl alcohol) hydrogel for biocatalytic application. II Farmaco 2001, 56, 541-547. 

When constructing biosensors, which are to be used continuously in vivo or in situ, maintaining sensor efficiency while increasing sensor lifetime are major issues to be addressed. Researchers have attempted various methods to prevent enzyme inactivation and maintain a high density of redox mediators at the sensor surface. Use of hydrogels, sol-gel systems, PEI and carbon paste matrices to stabilize enzymes and redox polymers was mentioned in previous sections. Another alternative is to use conductive polymers such as polypyrrole [123-127], polythiophene [78,79] or polyaniline [128] to immobilize enzymes and mediators through either covalent bonding or entrapment in the polymer matrix. Application to various enzyme biosensors has been tested. 

Mitala, J.J. and Michael, A.C. (2006) Improving the performance of electrochemical microsensors based on enzymes entrapped in a redox hydrogel. Analytica Chimica Acta, 556 (2),... 

In recent years, a growing Interest In hydrogels as solid supports for enzyme, hormones and pharmacons has become evident. Poly(hydroxyethyl) methacrylate), PHEMA, has been utilized to entrap trypsin and glucose oxidase (1 ) but the radical systems... 

Table III also shows that trypsln-cvb-hydrogel derivatives retain in the range of 11-45% the original enzyme activity, which is about average for the covalently bound trypsin on polymers containing hydrogel. For comparison, Mosbach (2.) immobilized trypsin on a crosslinked copolymer of acrylamide and hydroxyethyl-methacrylate via CNBr coupling, and analyzed it photometrically with a- -benzoyl-Dl-arginine-p-nltroanlllde (BAPNA), reporting a 35% retention of activity. o Driscoll and co-workers (1 ) however, reported an equivalent of 1.3% efficiency when trypsin was physically entrapped in a crosslinked PHEMA gel and assayed with TAME.

Enzymes, like most proteins, are unstable molecules. The stability of enzymes is of particular importance to biosensors because the rate of the enzymatically catalysed reaction is especially sensitive to the three-dimensional conformation of the enzyme. Most, if not all, enzymes are fully active only in a hydrated state. However, rarely are enzymes found in a completely aqueous medium in a sensor. Usually, the enzyme is dissolved into a hydrogel, immobilized onto a surface, or entrapped in a polymer matrix, all environments which differ in varying degrees from the natural environment of the enzyme. 

One approach to develop more biologically compatible surfaces for immobilizing proteins is to incorporate a matrix, such as a hydrogel, as an interface between the protein and the solid surface (Burnham et al. 2006). The entrapment of enzymes in a hydrogel layer provides excellent long-term stability and the possibility to adjust the polymer matrix to the specific needs of a certain enzyme. Hydrogels are useful for linking proteins to solid surfaces because their hydrophilic nature and porous structure can help to keep these labile molecules in the native functional state. 

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