Diverse applications of nanostructured diatom and ecotoxicity of carbon nanotubes to alga

Diatoms are unicellular, photosynthetic microalgae that are widely distributed in fresh and seawater. Frustules or the rigid amorphous silica cell wall of the diatoms have unique porous architecture and high surface area. Recent research shows the potential of nanostructure diatom silica for variety of applications including optics, photonics, bio sensing, filtration, immune precipitation, micro and nanofabrication, protein separation, catalysis and gas sensor. Diatom nanotechnology is not yet fully explored. The unique porous architecture of the diatom was utilized to immobilize various metal oxides like zirconium (Zr) oxide for fluoride removal, iron (Fe) oxide for arsenic removal and bimetallic Fe-Zr oxide for Selenium removal. The composites were characterized and adsorption data were modeled using First and Second order kinetics as well as Langmuir and Frendulich isotherms. The adsorption capacity for fluoride was 15.5 mg/g of diatom zirconium oxide composite, 10 mg/g of arsenite and 12.5 mg/g of arsenate using Diatom iron oxide composite and 227 mg/g of selenate using Diatom Zirconium iron oxide composite. Thus, new generation adsorbents for water treatment were successfully developed. Further, diatom silica was explored for drug delivery of hydrophobic drug Griseofulvin. Diatom drug composite (DDC) was developed using anti solvent crystallization method. DDC had 30% increased dissolution rate compared with pure drug. This research for the first time studied the use of laboratory cultured diatom for drug delivery of poorly water soluble drug. Another area research includes toxicity of carbon nanotubes to green algae Dunaliella tertiolecta. With increasing production and use of carbon nanotubes, it is important to study its effects on environment. Algae are present on the surface and are first point of contact, hence it’s important to understand the effects and interaction of these materials to algae. Carboxylated functionalized single walled carbon nanotubes (f-SWCNTs) were examined for their toxic effects on marine alga chlorophyte Dunaliella tertiolecta. The toxicity was measured based on growth, photosynthetic activities and oxidative stress measured as intracellular glutathione. Physical interactions between the f-SWCNT and alga were also examined. The presence of nanotubes led to a growth inhibition of over 30%, photosynthetic yield decreased by as much as 18% and intracellular glutathione reduction was as high as 95%. The results from f-SWCNTs were somewhat different when compared to our previous study using the same algae and functionalized multi walled carbon nanotubes