PhD Defence by Yanyan Su – University of Copenhagen

Plant and Environmental Sciences > Events > PhD Defence by Yanyan Su

PhD Defence by Yanyan Su

Title: Light manipulation and photonics applications of diatom frustules

Diatoms are eukaryotic, unicellular and photosynthetic algae that are ubiquitously present in almost every aquatic environment. Diatoms are one of the most dominant groups of phytoplankton, contributing more than 25% of the world’s net primary production. Apart from their enormous ecological significance, diatoms are distinguished by their unique, intricate and elaborate silica-based cell walls, with species-specific nanostructural patterns. Because of their many delicate structures at the micro/nano scale, diatoms offer a natural source for the production of nanostructured silica, which can inspire the nanotechnological capability of humans. More and more efforts have been made to attempt to utilize the diatom frustules for different applications purposes, but most of them are still in their infancy as most of these investigations are based on single valves. Further, in order to facilitate their applications, manipulation or control of the nanostructure of frustules is desirable.

The effect of different light spectra (six different wavelengths throughout the visible range at two light intensities) on the morphology of centric diatom Coscinodiscus granii has been investigated. It has been shown that different light spectra lead to significant changes in frustule morphology after 14 days of cultivation under different light treatments and that these changes in morphology is sufficient enough to cause the differences in photonic properties of the frustules.

Further work on the long-term effects of different ligth spectra on the frustule morphology has been carried out. It has been shown that C. granii could be maintained over a 10-months period at monospectral light and that most of the changes in frustule morphology induced by different light treatments could be maintained after 10 months cultivation and the variability in some of the morphological parameters was even reduced.
The effect of different light spectra on the cellular silicon concentration of C. granii has been studied. The change in cellular silicon concentration is mainly due to changes in the thickness of frustule. The potential adaptive mechanism might be related to adjustments in the sinking rates affected by controlling the cellular silicon concentration. This will eventually optimize the light utilization under different light treatments.

Finally, the spectral properties of drop-casted layers of both rinsed frustules and dried intact cells of three diatom species (Coscinodiscus granii, Thalassiosira punctifera and Thalassiosira pseudonana) have been investigated, with special focus on the transmission and reflectance in the UV range. It has been shown that rinsed frustules are more suitable as UV (or optical) filter compared with dried intact cells due to the instability in the spectral properties of the latter. Among the three tested diatom species, T. punctifera has the highest UV protection efficiency. There are no differences in the silica crystal structure of the frustules of the three diatom species and the differences in frustule morphology of the three diatom species might contribute to the differences in light propagation. Further, the thickness of the layer of the frustules is also a critical factor influencing the UV filtering effect.

Associate Professor Marianne Ellegaard, PLEN-UCPH
Associate Professor Nina Lundholm,  Natural History Museum of Denmark-UCPH

Assessment committee
Professor Poul Erik Jensen, Department of Plant and Environmental Sciences University of Copenhagen, PLEN-UCPH (chair)
Professor Anna Godhe, University of Gothenburg, Sweden
Senior Researcher Luca de Stefano, CNR Institute for Microelectronics and Microsystems

Reception at PLEN, Thorvaldsensvej 40 in M117-1 after the defence