Proc. Natl Acad. Sci. USA 109, 17336–17341 (2012)

The cell wall of silica-condensing microorganisms such as diatoms has a complex three-dimensional architecture that spans the nanometre- and millimetre-length scales. These structures and the biomineralization process of diatoms have inspired the creation of various functional inorganic nanomaterials. Previously, it was shown that highly concentrated protein hydrogels with a crowded three-dimensional molecular environment and user-defined features can be used as templates for creating porous silica replicas of the hydrogels. Now, Bryan Kaehr and colleagues at Sandia National Laboratories and the University of New Mexico have shown that crowded molecular environments such as mammalian cells can also direct the condensation of silica to form replicas of the cells.

Kaehr and co-workers grew cells on glass substrates and fixed them with formaldehyde before immersing them overnight in silicic acid at pH 3 at approximately 40 °C. Following this, the cells were dried and calcinated at 550 °C. Scanning electron microscopy showed this process coated the interior and exterior of the cell with silica, and that many of the details of the cells were faithfully captured. Moreover, the silicification process made the cellular architectures mechanically stable during drying and calcination. Further experiments revealed that although the lipid components of the cell membrane are gradually displaced during silica deposition, the cell membrane needed to be intact initially to maintain the mechanical integrity of the silica–cell composite. Even though the silica infiltrated all subcellular structures and organelles, the DNA helical structure remained undamaged in the nucleus.

The researchers also explored the transformation of the silica–cell composite into porous carbon structures, which could be useful in fuel-cell, decontamination and sensor applications.