Enzyme Immobilization On Magnetic Nanoparticles for Cellulose Hydrolysis

Cellulosic ethanol has received a lot of recent attention as an alternative transportation fuel to reduce global dependence on oil. However, due to the high cost of enzymes, the process is not currently economically feasible. Our approach is to formulate recyclable enzyme constructs by immobilizing cellulases on magnetic nanoparticles. Glucose oxidase was selected as a model enzyme to demonstrate the immobilization strategies. Three different size magnetic nanoparticles (5 nm, 25 nm and 50 nm) were fabricated to explore the effect of particle size on diffusion efficiency. Two different methods, co-precipitation and oxidation of Fe(OH)2 were used to fabricate different sizes of magnetic nanoparticles. Magnetic nanoparticles were functionalized with amine groups by 3-(amino propyl) triethoxysilane. Glutaldehyde was then used as a cross-linking agent between functionalized magnetic nanoparticles and glucose oxidase. We have found that activity of glucose oxidase immobilized on various size magnetic nanoparticles retained activity after more than 40 days. The analysis of transmission electron microscopy (TEM) images showed that the morphology of magnetic nanoparticles was spherical and that sizes agreed with results from those of Brunauer, Emmett, Teller (BET) method analysis. The magnetic strength of the nanoparticles was analyzed via a Physical Properties Measurement System (PPMS). X-ray photoelectron spectroscopy (XPS) confirmed each step of the magnetic nanoparticle surface modification and successful enzyme immobilization. Recycling stability studies showed that only 20% of activity loss occurred during 10 consecutive recycle for large (50 nm) and medium (25 nm) size enzyme magnetic nanoparticles. Cellulase multi-enzyme mixtures along with extra β-glucosidase are the key enzymes for biomass degradation. We are applying the immobilization methods to these biomass related enzymes to test the feasibility of recycling the biocatalysts during cellulose hydrolysis.