Development of silver nanoparticles via gamma radiation supported on mesoporous silica matrix for antimicrobial therapy

The Word Health Organization alerts about the "Post-antibiotic Era" eminence arrival when the microbes can be multi- resistant to all available drugs. The Covid-19 pandemic has caused a severe impact on increasing antimicrobial resistance. Therefore, the development of antibiotics substitutes is extremely important. Metallic nanoparticles, such as silver nanoparticles (AgNPs), are known for their antimicrobial properties. The AgNPs can be synthetized by gamma radiation, which can eliminate the use of toxic reducing agents, decrease the synthesis time and energy. However, these nanoparticles synthesis, as well as their insertion into biological systems, require a biocompatible stabilizing agent. The aim of this present work is to synthesize AgNPs by gamma radiation, supported by a mesoporous silica matrix, which is biocompatible, exhibit high surface area and great pore volume, what makes them suitable for biomedical applications. Moreover, a covalent functionalization on the nanocomposites surface with the antibiotic penicillin was proposed, aiming a synergistic bactericidal effect. The nanocomposites and the matrix were characterized by several techniques and the radiolytic synthesis parameters, i.e., dose, [Ag⁺], volume and pH, were statistically analyzed by the Minitab® factorial design. The increase of dose and pH raise the %Ag, while the increase of volume reduces it. UV-visible absorbance spectra and X-ray diffractograms confirm the metallic silver formation. Through gas adsorption analysis, it was possible to notice a surface area, volume and pore size reduction of the nanocomposite when compared to the matrix, suggesting that silver may be located inside the silica mesospores. This assumption could be reinforced by microscopy images, which revealed the formation of subnanometric AgNPs located inside the mesopores. Superficial nanoagglomerates of silver and silver oxide were found, also pointed out by X-ray photoelectron spectroscopy. The nanocomposite covalent functionalization was successful and there was approximately 7 wt% of penicillin incorporated, according to elemental and thermogravimetric analysis. Biological assays revealed a cell viability of the silica matrix and nanocomposites at a concentration up to 200µg/mL. (author)