Algae are a diverse group of autotrophic single-cell or multicellular organisms. Recently, applying algal research to nanoscience investigations has been one interesting area of emerging technology.
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Algae are categorized into microalgae (microscopic) and macroalgae (macroscopic). They can exist in colonies or individually in soil, marine, or fresh water, and some algal species are a rich source of nutrition for humans and animals.
Scientists have explored the potential use of algae in various fields of science and industry, which include medicine, pharmaceutical, agriculture, aquaculture, cosmetics, natural dyes, and biofuels. This article will discuss algae-based approaches in nanotechnology research.
Algal Research and Nanotechnology
Algae species can be classified into different groups, such as Chlorophyceae, Cyanophyceae, Phaeophyceae, Rhodophyceae. Microalgae in particular have been used to synthesize metallic nanoparticles as well as bimetallic nanoalloys in a dose-dependent manner.
Algal research has observed that green synthesis of nanomaterials using algae has several advantages, including maximum reduction of metals and a higher rate of synthesis, which might be due to their high metal accumulation capacity.
Another advantage is that, compared to other microbes, algal cultures are relatively easy to handle and can be grown at low temperatures. Recently, algae-based biosynthesis of nanomaterials is considered a new branch of algal research, namely, phyconanotechnology.
Biosynthesis of Nanomaterials Using Algal Research
Nanomaterials of desirable shape and particle size could be obtained by altering physical parameters such as temperature, pH, the concentration of the metals and the reducing agent.
These parameters also prevent aggregation and agglomeration of the nanomaterials. Some of the common steps involved in the biosynthesis of metallic nanoparticles are discussed below:
- Preparation of algal extract in aqueous or organic solvents.
- Preparation of molar solutions of the ionic metallic compounds.
- Mixing of the previously prepared algal extract with the molar solution of the ionic metallic compounds and subsequent incubation for a specific time under controlled conditions in a continuous stirring or stagnant position.
Based on the type of microalgae species, nanoparticles are synthesized either by an extracellular or an intracellular technique. During the extracellular formation of metallic nanoparticles, a reduction reaction occurs outside the algal cells.
The extracellular enzymes and metabolites, such as polysaccharides, reducing sugars, proteins, peptides, pigments, or other reducing factors, can reduce the metal ions and, thereby, produce metallic nanoparticles.
In contrast, the reduction of metallic ions is associated with algal metabolism (photosynthesis and respiration) for the intracellular formation of metallic nanomaterials.
In cyanobacteria, some of the key components associated with the reduction of metallic ions to metallic nanoparticles are reduced nicotinamide adenine dinucleotide phosphate (NADPH) and NADPH-dependent reductase, recycled through energy-generating reactions occurring in the photosynthetic electron transport system (ETS).
A smaller degree of conversion also appears in respiratory ETS. Other components where formation occurs via redox reactions are the thylakoid membrane, cell membrane, and cytoplasm.
Algal research also reports that the enzyme nitrogenase is associated with the intracellular reduction of gold (Au) ions to gold nanoparticles (AuNPs). Interestingly, it was found that metallic nanoparticles are first synthesized intracellularly by internalization of the metallic ions.
Subsequently, internal reduction and release of stabilized metal nanoparticles into the culture medium occur due to the function of polysaccharides and other macromolecules.
pH also plays an important role in the extracellular synthesis of metallic nanoparticles. For instance, a higher pH level enhances the reducing power of functional groups, increasing stability and preventing their agglomeration of the synthesized metallic nanoparticles.
The color of the reaction mixture changes when nanomaterials (e.g., gold and silver) are produced. For instance, if the color of the reaction mixture changes to brown, it is indicative of the formation of silver (Ag) nanoparticles, while in the case of Au nanoparticles formation, the color of the reaction mixture changes to pink or ruby red.
The biosynthesized nanoparticles are characterized using various analytical tools, such as U.V. Visible Spectrometer (UV Vis), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transformed Infrared (FTIR) spectroscopy, Energy-Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD).
Applications of Algal Synthesized Nanomaterials
Several nanoparticles synthesized using algae-based processes possess unique physical properties and are used in many industries, such as biomedical, water treatment, and agriculture.
Antibacterial
Copper nanoparticles synthesized using brown alga (Bifurcaria bifurcate) exhibit robust antibacterial activity against Staphylococcus aureus, Enterobacter aerogenes, etc. Similarly, AuNPs produced using Galaxaura elongata show antibacterial activity against Pseudomonas aeruginosa, MRSA, and E. coli. Ag nanoparticles biosynthesized using whole cells of microalga Chlorococcum humicola can inhibit multiple bacteria.
Additionally, Ag nanoparticles produced using Caulerpa racemose, a marine algae, have been found to effectively inhibit human bacterial pathogens, such as S. aureus and Proteus mirabilis. The aqueous extract of Gracilaria corticata, a red algae, has been used as a reducing agent to generate Ag nanoparticles, which can inhibit phytopathogens, such as Xanthomonas campestris pv. malvacearum.
Antifungal
Nanoparticles synthesized using algal research act as efficient antifungal agents. For example, Ag nanoparticles synthesized using red seaweed Gelidiella acerosa are effective against Humicola insolens, Trichoderma reesei, Fusarium dimerum, and Mucor indicus.
Another algal research study reported Ag nanoparticles produced using Sargassum longifolium could inhibit Aspergillus fumigatus and Fusarium sp.
Anticancer
Scientists reported that Ag nanoparticles, synthesized using Sargassum vulgare, could effectively eliminate cancerous human myeloblastic leukemic cells HL60 and cervical cancer cells HeLa.
Antioxidant
Au nanoparticles synthesized using freshwater epilithic red alga, Lemanea fluviatilis exhibit robust antioxidant properties.
Future Prospects
One area of nanotechnology that algal research could further benefit from is the exploration of nanoparticles as an antibiofilm. Silver, selenium and tellurium nanoparticles, which can be produced via algae-based biosynthesis, have shown strong antibiofilm activity against both Gram-positive and Gram-negative pathogens.
In the future, algal research could contribute to the eco-friendly production of biofilms, aiding nanotechnology research's ongoing move towards green science.
Continue reading: Using Single Cell ICP-MS to Measure the Increase in Nanoparticles and Ionic/Dissolved Gold by Fresh Water Algae.
References and Future Reading
Mukherjee, A. et al. (2021) A Review of Green Synthesis of Metal Nanoparticles Using Algae. Frontiers in Microbiology. 12. Available at: https://doi.org/10.3389/fmicb.2021.693899
Gupta, R. and Agarwal, N. (2019) Advances in Synthesis and Applications of Microalgal Nanoparticles for Wastewater Treatment. Journal of Nanotechnology. Article ID 7392713. pp. 9. https://doi.org/10.1155/2019/7392713
Dahoumane, A. S. et al. (2016) Microalgae: An outstanding tool in nanotechnology. Bionatura. 1(4). Available at: https://doi.org/10.21931/RB%2F2016.01.04.7
Oscar, L. F. et al. (2016) Algal Nanoparticles: Synthesis and Biotechnological Potentials. Algae - Organisms for Imminent Biotechnology, edited by Nooruddin Thajuddin, Dharumadurai Dhanasekaran. IntechOpen. https://www.intechopen.com/chapters/50544
Sharma, A. et al. (2016). Algae as crucial organisms in advancing nanotechnology: a systematic review. Journal of Applied Phycology. 28. Available at: https://link.springer.com/article/10.1007/s10811-015-0715-1
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