Diatoms are a plankton, whose shells are made of silica. Their ability to make silica structures, biosilicification, has been of interest in nanotechnology and materials sciences, because biosilicification occurs under ambient conditions at slightly acidic pH values, and the degree of complexity of the resulting nanometer-scale structures has never been matched by artificial materials. Biosilicification in diatoms is achieved by specific interactions between silicic acid derivatives and cationic polypeptides named silaffins containing long-chain polyamines. Biosilicification, therefore, has mainly been achieved by controlling the structure of cationic polymers. Quaternized poly(2-(dimethylamino)ethyl methacrylate) films formed by surface-initiated atom transfer radical polymerization were chose as a synthetic counterpart of the long-chain polyamines in silaffins. Counteranion exchange controlled the structure of the silica films. In addition, we demonstrated that poly(2-(dimethylamino)ethyl methacrylate) film could be used for the formatio of nonbiogenic oxide thin films, such as TiO2.
On the other hand, the spatio- and chemoselective deposition of silica was achieved on the poly(diallyl dimethyl ammonium chloride) film formed by layer-by-layer processes.
With a help of the physiological conditions of the layer-by-layer processes and biosilicification, a living cell was individually encapsulated by silica without loss of viability.