Synthesis of Si/SiO2 core/shell fluorescent submicron-spheres for monitoring the accumulation of colloidal silica during the growth of diatom Chaetoceros sp.

Marine diatoms play a very crucial role in carbon export, and current food-web and become an important factor in global silica cycle. This then has made the mechanism of their biosilicification interesting to be a research subject. The classical theory states that the silica metabolism has been originated from the absorption of silicate ions, which might not give a suitable explanation for the solid silica silicification. In this study, mono-disperse Si/SiO2 fluorescent submicron-spheres were synthesized in aqueous solution, and applied in monitoring the extracellular solid silica accumulation of Chaetoceros sp. diatom. The Si/SiO2 submicron particles emitted light-blue color with the spectrum centered at 440 nm under the excitation of 365 nm UV light, similar to the typical excitation/emission pair of the DAPI fluorophore (excitation/emission: 358 nm/461 nm).  The fluorescence-microscopic investigation showed that the Si/SiO2 particles delocalized on the diatoms’ surface and increased a silicic-acid-level surrounding the microalgae. As a consequence, the growth rate of the diatoms increased as the concentration of the SiO2 particles was at 120 mg/L, and reached 1.5 times higher than the growth rate calculated from the F2 media. The study not only introduces a new aspect to the extracellular metabolism of microalgae biosilicification corresponding to the global silica cycle, but also presents a new-type of culturing media using SiO2 nanoparticles for diatom cultivation, which increases the growth rate of artificial diatom-culturing for further applications.