Biomimetic Silica Encapsulation of Nanoparticles and Enzymes

Abstract

In nature, several organisms elegantly deposit silica into shell and spicule structures. These include the unicellular algae family of diatoms (1, 2) as well as the marine sponges (3, 4). The basis for silica deposition in these organisms has been elucidated over the last several years. Families of proteins, termed silaffins in diatoms and silicateins in marine sponges, have been isolated from the silacious components of the respective organisms (1, 3). These protein families do not resemble each other in terms of sequence or isoelectric point, but the purified forms of each precipitate silica from silicic acid precursors (1, 4). The in vitro protein-mediated silica condensation reactions were the proof-of-concept that these organisms use proteins to deposit and/or template their intricate silica structures. Interestingly, these silica precipitating templates become entrapped with the silica matrix. The composite protein-silica structure found in nature was the impetus for encapsulating enzymes in silica using peptides and proteins as the silica template. This chapter will focus on the encapsulation of nanoparticles and enzymes using peptide-templated silica.