Characterization of Silver Nanoparticle Systems from Microalgae Acclimated to Different CO₂ Atmospheres

Green synthesis of metallic nanoparticles using microalgae exposed to high CO₂ atmospheres has not been studied in detail; this is of relevance in biological CO₂ mitigation systems where considerable biomass is produced. In this study, we further characterized the potential of an environmental isolate Desmodesmus abundans acclimated to low and high CO₂ atmospheres [low carbon acclimation (LCA) and high carbon acclimation (HCA) strains, respectively] as a platform for silver nanoparticle (AgNP) synthesis. As previously characterized, cell pellets at pH 11 were selected from the biological components tested of the different microalgae, which included the culture collection strain Spirulina platensis. AgNP characterization showed superior performance of strain HCA components as preserving the supernatant resulted in synthesis in all pH conditions. Size distribution analysis evidenced strain HCA cell pellet platform (pH 11) as the most homogeneous AgNP population (14.9 ± 6.4 nm diameter, -32.7 ± 5.3 mV) followed by S. platensis (18.3 ± 7.5 nm, -33.9 ± 2.4 mV). In contrast, strain LCA presented a broader population where the size was above 100 nm (127.8 ± 14.8 nm, -26.7 ± 2.4 mV). Fourier-transform infrared and Raman spectroscopies showed that the reducing power of microalgae might be attributed to functional groups in the cell pellet from proteins, carbohydrates, and fatty acids and, in the supernatant, from amino acids, monosaccharides, disaccharides, and polysaccharides. Microalgae AgNPs exhibited similar antimicrobial properties in the agar diffusion test against Escherichia coli. However, they were not effective against Gram (+) Lactobacillus plantarum. It is suggested that a high CO₂ atmosphere potentiates components in the D. abundans strain HCA for nanotechnology applications.