From Microalga to Nanomaterials: Green Synthesis of Silver Nanoparticles from Spirulina platensis

This study describes the synthesis and characterization of silver nanoparticles (AgNPs) using two Spirulina platensis extracts: one cultivated in a bioreactor in Bulgaria (near Varvara village), and the other from the local market in Bulgaria (Dragon Superfoods). To assess their properties and stability, ATR-FTIR, TEM (Transmission Electron Microscopy) images, and zeta potential were used. The chemical content of the extracts and AgNPs obtained were assessed, as well as their antimicrobial and anti-inflammatory activities. We found that the extracts’ origin significantly influenced nanoparticle morphology, surface charge, and bioactivity. AgNPs were spherical and different in size from Bioreactor 4–8 nm, while Dragon obtained larger particles of about 20 nm. We found that synthesis altered the chemical content of the extracts, particularly in lipid, protein, and tocopherol content, suggesting active involvement of Spirulina-derived biomolecules in nanoparticle formation. Antimicrobial assays showed slightly higher activity for Dragon AgNPs against P. aeruginosa (21 mm) and S. enteritidis (23 mm), with similar effects against L. monocytogenes and S. aureus. At 2.5 mg/mL, both samples protected human albumin from thermal denaturation more effectively (23.36% and 20.07%) than prednisolone (16.99%). Based on the obtained results, AgNPs from Spirulina platensis can be attributed as multifunctional agents with anti-inflammatory and antimicrobial activity.