“Converting free enzymes into these novel enzyme-containing nanoparticles can result in significantly more stable catalytic activity,” said Jay Grate of the Pacific Northwest National Laboratory.
To coat the enzymes, Grate and colleague Jungbae Kim used a porous composite organic/inorganic network just a few nanometres thick. First the researchers formed vinyl groups on the surface of the enzymes to make them soluble. Then they mixed a solution of the enzymes in an organic solvent with silane monomers containing both vinyl groups and trimethoxysilyl groups. Polymerization of these monomers produced linear polymers covalently bound to the surface of the enzyme. A second polymerization step then cross-linked the silicon chains, creating a composite network around each enzyme molecule. Changing the reaction conditions and reactants altered the thickness of the network: for example, using less reactive vinyl groups produced a coating up to half as thick.
The researchers applied the coating to the protein-splitting enzyme alpha-chymotrypsin, forming single-enzyme nanoparticles about 8 nm in diameter. The nanoparticles had a half-life of up to 143 days. A solution of the particles stored at 4 °C, meanwhile, showed only a slight decrease in activity over five months.
The single-enzyme nanoparticles could have applications in biosensors, breaking down toxic waste, and surface coatings - for example to protect implants in the body from the formation of protein plaques or on ships to prevent barnacles from attaching to the hull.
The researchers reported their work at the American Chemical Society meeting held in the US earlier this month.