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Diatoms are microalgae which have their unique cell encased into a nanostructured silica shell called frustule. The silica shells of diatoms can be envisioned as micro/nano structures suitable to further chemical modification yielding smart functional nanomaterials. Differently from the chemical production of silica, the biosynthesis of natural SiO2 occurs in mild conditions and it does not require the use of toxic precursors or reagents. Biosilica from diatoms features interesting properties such as high surface area, mechanical resistance and nanotexturization, which makes it appealing for applications in photonics, sensing, optoelectronics, biomaterial science and biomedicine. In addition, frustules’ biosilica can be easily chemically modified to add new functions. This can be done by simple surface functionalization, and/or in vivo by adding specific molecules to the culture medium. We have shown applications of chemically modified frustules for bone cells growth. In particular, we have demonstrated that in vivo functionalization of diatom biosilica with sodium alendronate results in osteoactive material. We have also demonstrated the production of functional structures by coating living diatoms with biomimetic organic polymers, like polydopamine (PDA). The resulting living heterostructures turn out to be intriguing platforms for additional chemical modifications, such as anchoring enzymes, affording multifunctional materials for biological applications. Finally, we have also shown that photonic microstructures can be produced by in vivo incorporation of tailored light emitting molecules in living Thalassiosira weissflogii diatoms. With a similar approach, biosilica has been doped with phosphorescent Ir complexes. Overall, our studies point out intriguing biotechnological routes to multifunctional nanomaterials for biomedicine and nanotechnology starting from unicellular algae.
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