4.3.3. Other Polymeric Matrices

Hydrogels are polymeric networks that are of great interest for protein immobilization because they present the double advantage of high water content and a tunable porous structure [162]. Natural polysaccharides such as alginate can produce beads when crosslinked with certain metals. Alginate concentration can be tuned to control the porosity of alginate beads (in the range 5 to 200 nm diameter) and to find the best compromise between substrate diffusion and enzyme conformation preservation and leaching [163]. Enzymes embedded in DNA hydrogels often show enhanced thermal stability and improved stability during freeze-thaw cycles or in the presence of denaturants such as organic solvents. Conformation of the enzyme is proposed to be maintained thanks to extensive inter- and intra-strand weaving of long DNA building blocks. The hydrophilicity of the hydrogel further protects the enzyme against organic solvent [164]. Gel nanofiber made of Zn2+ and adenosine monophosphate was also used to encapsulate an enzyme cascade for glucose

detection. The biomaterial exhibited enhanced stability against temperature variation, protease attack, extreme pH, and organic solvents. Porosity and water content of the gel allowed to maintain 70% of the activity after 15 days storage while free enzymes lost activity [165].
