Nanoparticles filter light for microalgal growth

Researchers from The University of Western Australia (UWA) have helped develop a nanoparticle light filter system which stimulates the growth of useful microalgal organisms. The resulting microalgal cells, and their light-absorbing photopigments, provide high value-added chemical compounds which could lead to a variety of environmentally sustainable applications.

Research Assistant Professor Ela Eroglu and Dr Paul Eggers worked with Winthrop Professor Steven Smith and Flinders University clean technology expert Professor Colin Raston on the filter system. Their research has been published in the Royal Society of Chemistry journal Green Chemistry.

Algae grow in natural light but too much light, or certain wavelengths of light, can inhibit its growth. The researchers developed a method of using gold and silver nanoparticles to create an optical nanofilter within a bioreactor. Their technique involved the use of localised surface plasmon resonance (LSPR) - “the interaction between the electric field component of light and the conduction band electrons of a metal nanoparticle which leads to an oscillation of the surface electrons at a resonant frequency”, the researchers explained.

This harnesses the light wavelengths most beneficial to microalgal pigment formation, resulting in improved growth. Advantages of the method are that the bioreactors are re-usable systems and, as the researchers state, “Efficient recycling of these nanoparticle suspensions has been successively achieved for more than five cycles within an experimental period of six months”.

While Dr Eroglu admitted that “commercial application is a long way off”, the researchers say the usefulness of the microalgal cells means “their large-scale economic production is commercially desirable”. Potential applications include medical antioxidants and anti-inflammatory agents, natural food and soap colourants, cosmetic agents and feed supplements in aquaculture.

“Perhaps even more exciting,” said Professor Smith, “is the potential to use such nanofilters in artificial photosynthesis systems - the ‘Holy Grail’ of Green Chemistry - in which solar energy would be used to split water into oxygen and hydrogen for fuel.”

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