ENCAPSULATION OF MICROALGAE IN SILICA AND THEIR POTENTIAL USE AS BIOREACTORS FOR SYNTHESIS OF METALLIC NANOPARTICLES

ANA CECILIA SPEDALIERI; MATIAS JOBBAGY; ALDABE BILMES, SARA

Madrid

Congreso; XVII International Sol-Gel Conference; 2013

International Sol-Gel Society (ISGS)

Encapsulation of microorganisms in silica sol-gel matrices provides an interesting approach towards developing bioactive hybrid materials. The optical and mechanical properties of the inorganic matrix along with the capability of microorganisms for releasing biomolecules or modifying their surroundings can provide many novel characteristics to this type of material. Moreover, the capability of several microorganisms of biosynthesizing metallic nanoparticles enables the possibility of developing bioreactors of nanoentites with controlled size and shape. In this work we present the biosynthesis of gold nanoparticles by microalgae -mainly Chlorella vulgaris- encapsulated in SiO2. The encapsulation methodology consists in a two-step process in which the algae are fixed in calcium alginate beads, and the SiO2 matrix is then formed around the bead by a sol-gel process. Once the gel is formed a citrate solution is added to dissolve the calcium alginate, generating a small cavity where cells can grow. The biosynthesis of gold nanoparticles by the encapsulated microalgae from gold cations was made by adding Au precursors either in the pre-encapsulation process or after the gel is formed. The formation of alginate beads using HAuCl4 as the cation precursor produced biosynthesized 10-15nm Au NPs, demonstrating bioavailability of gold cations. Moreover, composition of the beads was further analyzed, concluding the crosslinking cations were protons. For the addition of gold cations after the gel is formed ?HAuCl4 solution added on top of gels-, beads formed with calcium alginate and proton alginate were used. This latter composition was more suitable for lowering inespecific reduction of gold, since no citrate was needed and the bead dissolved by itself once the gel is formed. In terms of the inorganic matrix, two different synthetic pathways were analyzed. We used a sol-gel aqueous pathway, using sodium silicate and Ludox, and an alcoxide route, starting with TEOS, and studied the synthetic conditions that allowed minimum cellular stress and proper diffusion of the biosynthesized nanoparticles. Gels obtained by using TEOS as a precursor gave better optical properties, which is fundamental for proper growth of microalgae since they are photosynthetic organisms. Throughout this work we analyzed the influence of the pre-encapsulation and post-encapsulation conditions for biosynthesis and the optimal conditions of the inorganic matrix to allow release of the metallic nanoparticles. As concluding remarks, this biohybrid material is suitable for developing bioreactors for synthesis of monodisperse gold nanoparticles, and potentially expandable to other metallic nanoparticles and microalgae species.