Aerogels are famously among the solids with the lowest density and various applications have been suggested since their discovery. Now, a team from Israel has developed a general way to entrap enzymes within the airy hollows of these novel materials. They hope to exploit the low density, high surface area, high porosity, and ultra-low heat conductivity in their novel composites. Aerogels can have a density as low as 3 milligrams per cubic centimeter and a surface area of 1000 square meters per gram.

Supported, or immobilized, enzymes, are critical components of numerous biotechnological processes, such as fructose-glucose isomerization and stereoselective drug modification. The benefits of the immobilization of the enzyme is that it can be highly active during the reaction, protected from damage, and then easily removed for use again once the reaction is complete.

The team points out that early attempts to use pure ceramic aerogels such as inert silica as an entrapping support material for enzymes were not successful because the very procedures used to synthesize the aerogels are destructive to the enzymes . Conversely, tweaking the procedure to make it compatible with enzyme form and function disrupts the formation of the aerogel. The team of David Avnir of The Hebrew University of Jerusalem has now found a general way to circumvent both of these problems to allow the entrapment of enzymes in silica aerogels, retaining enzymatic activity and the air-light structure of the aerogel.

The process, developed by graduate student Nir Ganonyan, utilizes ethanol as an intermediate co-solvent much later and in lower quantity, and reduces significantly the temperature and time needed for the drying with a supercritical fluid (carbon dioxide), all of which minimize enzyme denaturing. Precise buffer control in terms of concentration and timing also accelerated gelation without denaturing the enzymes. The precise details are critical to their success. [Avnir et al. Mater Today (2019); DOI: 10.1016/j.mattod.2019.09.021]

The team explains how their entrapment of three different types of enzymes - glucose oxidase, acid phosphatase, and xylanase - was possible. Moreover, the aerogel-supported enzymes all showed superior activity and classical Michaelis-Menten kinetics (when compared to the same enzymes supported on a more conventional xerogel by sol-gel entrapment). The team adds that the next phase in this work will be to modify the silica itself to expand its potential applications and also to investigate the potential of other oxides in the structures, namely alumina and iron oxide, which have regulatory approval for use in humans.