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

Green synthesis ofmetallic nanoparticles using microalgae exposedto high CO2 atmospheres has not been studied in detail;this is of relevance in biological CO2 mitigation systemswhere considerable biomass is produced. In this study, we furthercharacterized the potential of an environmental isolate Desmodesmus abundans acclimated to low and high CO2 atmospheres [low carbon acclimation (LCA) and high carbonacclimation (HCA) strains, respectively] as a platform for silvernanoparticle (AgNP) synthesis. As previously characterized, cell pelletsat pH 11 were selected from the biological components tested of thedifferent microalgae, which included the culture collection strain Spirulina platensis. AgNP characterization showedsuperior performance of strain HCA components as preserving the supernatantresulted in synthesis in all pH conditions. Size distribution analysisevidenced strain HCA cell pellet platform (pH 11) as the most homogeneousAgNP 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 LCApresented a broader population where the size was above 100 nm (127.8 +/- 14.8 nm, -26.7 +/- 2.4 mV). Fourier-transform infraredand Raman spectroscopies showed that the reducing power of microalgaemight be attributed to functional groups in the cell pellet from proteins,carbohydrates, and fatty acids and, in the supernatant, from aminoacids, monosaccharides, disaccharides, and polysaccharides. MicroalgaeAgNPs exhibited similar antimicrobial properties in the agar diffusiontest against Escherichia coli. However,they were not effective against Gram (+) Lactobacillusplantarum. It is suggested that a high CO2 atmosphere potentiates components in the D. abundans strain HCA for nanotechnology applications.