Otimização da síntese verde de nanopartículas de prata para incorporação em gel antimicrobiano

Abstract

Silver nanoparticles (AgNPs) have gained proeminence due to application in pharmaceuticals, textiles and hygiene products. The AgNPs are synthesized by chemical and physical methods, however these processes have high costs and generate pollutants. On another hand, the green synthesis or biosynthesis emerges as an alternative route, using biological systems to intermediate the synthesis of AgNPs. The aim of this study was to investigate the effect of pH, temperature and silver nitrate (AgNO3) concentration on the silver nanoparticles (SNP) synthesis by Aspergillus flavo-furcatis to develop a polymeric gel with antimicrobial properties. A full-factorial experiment 2³ was performed to assess the effect of physicochemical conditions on AgNP synthesis. The antimicrobial activity of synthesized AgNPs were performed using well-agar diffusion and broth microdillution methods, to determine the minimal inhibitory concentration (MIC) against Staphylococcus aureus, Escherichia coli and Candida albicans. The characterization of AgNPs that showed lower MIC values were performed by UV-Vis spectroscopy, dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS). A polymeric gel was developed using the synthesized AgNPs and Carbopol 940 as gelificant, with evaluation of visual aspect and pH. The incorporation of AgNPs into the gel matrix was confirmed by AFM. The nanocomposite was tested against S. aureus, E. coli and C. albicans using agar well diffusion method. The pH and AgNO3 concentration had significant effects on the AgNPs synthesis in the experimental conditions. The AgNPs synthetized at pH 9,0 and 1,5 mM AgNO3 were more effective against S. aureus (3,17 µg/mL), E. coli (6,35 µg/mL) e C. albicans (0,79 µg/mL). The AgNPs showed a spherical form (average size of 58 nm), Zeta potential of -32,5 mV and showing exclusively silver in microcrystalline structure with the presence of protein residues as possible capping agents. The nanocomposite inhibited the growth of S. aureus (15,7 ± 0,6 mm), E. coli (13,7 ± 0,3 mm) e C. albicans (12,3 ± 0,4 mm). These data support that AgNP synthesis by A. flavo-furcatis is influenced by pH and AgNO3 concentration, and the synthesized AgNPs are stable in colloidal solutions, demonstrating a potential in the development of nanocomposites for the control of opportunistic and pathogenic microorganisms.