Biossíntese e caracterização de nanopartículas de ouro a partir de extratos de flores e folhas de Calliandra dysantha: potencial antioxidante e antibiofilme

Abstract

Nanotechnology is a research field that explores materials with nanometric dimensions, integrating knowledge from chemistry, physics, biology, and engineering to develop, manipulate, and apply these materials with unique properties. Among nanomaterials, gold nanoparticles are notable due to their physicochemical, optical, and biological properties. Green synthesis mediated by plant extracts represents a sustainable alternative to traditional physical and chemical methods, as it employs bioactive compounds capable of acting as reducing, stabilizing, and antimicrobial agents. Furthermore, antimicrobial resistance and bacterial biofilm formation represent significant public health challenges, as they hinder the efficacy of conventional treatments and promote infection persistence. Thus, this study aimed to perform, for the first time, the biosynthesis of gold nanoparticles using methanolic extracts from the flowers and leaves of Calliandra dysantha, a species native to the Brazilian Cerrado, as well as to characterize the resulting nanoparticles and evaluate their antioxidant and anti-biofilm potential against Staphylococcus aureus. Therefore, the present study aimed, for the first time, to biosynthesize gold nanoparticles using methanolic extracts of flowers and leaves of Calliandra dysantha, a species native to the Brazilian Cerrado, as well as to characterize these nanoparticles and evaluate their antioxidant and antibiofilm potential against Staphylococcus aureus. Gold nanoparticles were synthesized in aqueous medium using tetrachloroauric acid as the metal precursor under heating and stirring. Nanoparticle formation was confirmed by the presence of absorption bands at approximately 528 nm. Transmission electron microscopy analyses revealed the formation of spherical particles, with an average diameter of 13.8 ± 3.4 nm for gold nanoparticles synthesized with flower extract (F-AuNPs) and 20.8 ± 12.7 nm for those synthesized with leaf extract (L-AuNPs). The mean hydrodynamic diameters were 64.47 ± 10.62 nm for F-AuNPs and 80.55 ± 0.04 nm for L-AuNPs, with low polydispersity indices. Zeta potential values indicated moderate colloidal stability with low aggregation propensity of the dispersions. Assays performed using the DPPH and ABTS methods at concentrations ranging from 125 µg/mL to 15.625 µg/mL demonstrated high antioxidant activity in the plant extracts, suggesting the presence of antioxidant compounds that may contribute to the biosynthesis and stabilization of the nanoparticles. Antioxidant assays using the DPPH and ABTS methods at concentrations ranging from 125 µg/mL to 15.625 µg/mL demonstrated the high antioxidant activity of the plant extracts, suggesting the presence of antioxidant compounds that may contribute to the biosynthesis and stabilization of the nanoparticles. Conversely, the nanoparticles themselves exhibited low antioxidant activity, possibly due to decreased availability of bioactive compounds after synthesis. In the antibiofilm assay, all treatments showed higher activity at a concentration of 125 µg/mL. At this concentration, no significant differences were observed between treatments, indicating that both the extracts and the gold nanoparticles were able to significantly reduce the metabolic viability of Staphylococcus aureus biofilms. Thus, the results demonstrate that flower and leaf extracts of Calliandra dysantha have potential for the biosynthesis of gold nanoparticles with relevant physicochemical characteristics and antioxidant and antibiofilm activities, highlighting their potential for future biotechnological and biomedical applications.