Biossíntese de nanopartículas de prata utilizando extratos metanólicos de Calliandra dysantha: caracterização e avaliação da atividade antimicrobiana

Abstract

The resistance of bacteria and fungi to conventional antimicrobial agents represents one of the major challenges in public health, driving the search for new therapeutic strategies. In this context, approaches based on nanotechnology and the use of bioactive molecules derived from Cerrado plants have contributed to the development of functional materials with biomedical potential. The green biosynthesis of silver nanoparticles (AgNPs) has emerged as a promising and sustainable alternative, as bioactive compounds present in plant extracts act simultaneously as reducing and stabilizing agents, minimizing the use of potentially toxic reagents. Therefore, this study aimed to synthesize AgNPs using methanolic extracts from leaves, flowers, stems, and roots of Calliandra dysantha, characterize the obtained nanoparticles, and evaluate their antimicrobial activity against Staphylococcus aureus, Escherichia coli, Talaromyces sp., and Rhodotorula mucilaginosa. The biosynthesis was performed in an aqueous medium using silver nitrate as a precursor under constant heating and stirring. The AgNPs were characterized by ultraviolet-visible absorption spectroscopy (UV-Vis), dynamic light scattering (DLS), and zeta potential analysis. Analyses of antioxidant potential were performed using the DPPH, ABTS, and ferric reducing power assays with the flower and leaf extracts. The antimicrobial activity was evaluated using the disk diffusion method. The formation of AgNPs was confirmed by the presence of a localized surface plasmon resonance (LSPR) band between 430 and 450 nm, with higher synthesis efficiency observed for flower and leaf extracts. DLS analyses revealed mean hydrodynamic diameters of 24.86 nm and 39.65 nm for AgNPs synthesized using flower and leaf extracts, respectively, with low polydispersity indices and zeta potential values of −23.3 mV and −24.0 mV, indicating moderate colloidal stability. In disk diffusion assays, no inhibition halos were observed for either AgNPs or plant extracts against the evaluated microorganisms, suggesting the need for optimization of synthesis conditions and sample concentrations, as well as the application of quantitative methods for antimicrobial activity assessment. It is concluded that C. dysantha has potential for the green synthesis of AgNPs with physicochemical characteristics consistent with those described in the literature, representing a promising source of biomolecules with antioxidant properties for the sustainable development of nanomaterials with possible applications in nanobiotechnology.