An overview of the fundamentals of the chemistry of silica with relevance to biosilicification and technological advances

Biomineral formation is widespread in nature, and occurs in bacteria, single-celled protists, plants, invertebrates, and vertebrates. Minerals formed in the biological environment often show unusual physical properties (e.g. strength, degree of hydration) and often have structures that exhibit order on many length scales. Biosilica, found in single-celled organisms through to higher plants and primitive animals (sponges), is formed from an environment that is undersaturated with respect to silicon, and under conditions of approximately neutral pH and relatively low temperatures of 4-40 degrees C compared to those used industrially. Formation of the mineral may occur intracellularly or extracellularly, and specific biochemical locations for mineral deposition that include lipids, proteins and carbohydrates are known. In most cases, the formation of the mineral phase is linked to cellular processes, an understanding of which could lead to the design of new materials for biomedical, optical and other applications. In this contribution, we describe the aqueous chemistry of silica, from uncondensed monomers through to colloidal particles and 3D structures, that is relevant to the environment from which the biomineral forms. We then describe the chemistry of silica formation from alkoxides such as tetraethoxysilane, as this and other silanes have been used to study the chemistry of silica formation using silicatein, and such precursors are often used in the preparation of silicas for technological applications. The focus of this article is on the methods, experimental and computational, by which the process of silica formation can be studied, with an emphasis on speciation.