Silver Nanoparticles Formation by Phaeodactylum tricornutum Cells

Diatoms (Bacillariophyceae) are eukaryotic unicellular autotrophic organisms and the most species-rich group of algae. Diatoms are characterized by a silicified cell wall called a frustule that consists of two parts called thecae.

The study of nanomaterials has been emerging throughout the last few decades due to their incredible applications in all aspects of human life. The synthesis of nanoparticles has been extensively studied due to their specific characteristics such as catalytic activity and antimicrobial capabilities.

Diatom cells have a great diversity of geometrical shapes and their ideal hierarchy structure is a promising system for green synthesis of nanomaterials like nanoparticles (NPs) and other nanomaterials while reducing the cost and the toxic substances often used. Silver nanoparticles (AgNPs) synthesis using natural organisms has become a major research area in the field of nanotechnology. Therefore, AgNPs biosynthesis by diatom cultures, which can be done at ambient CO₂ concentrations, temperature and pressure, offers a sustainable green alternative solution.

In this work, we examined the formation of silver NPs (AgNPs) by the diatom P. tricornutum cultivated at 25°C for a period of 8 days. Using this approach, diatom cultures were grown throughout the duration of the experiment in an artificial seawater (ASW)-f/2 medium where 1 ppm Ag⁺ was added on experimental day 4. As seen in previous results, 1 ppm Ag⁺ reduces the P. tricornutum growth by up to 50% as compared with the control. Scanning Electron Microscopy (SEM) in combination with Energy Dispersive Spectrometry (EDS) revealed the presence of AgNPs nanoparticles with different sizes which 80% of them were under 100 nm associated with the diatom frustules and extracellular polysaccharides. These results open new possibilities in the development of new bionanomaterials by diatoms.