Optimization of synthesis conditions and physicochemical characterization of silver nanoparticles by cell lysate of lactobacillus rhamnosus

Abstract

Nanomaterials have been present throughout history and, in 1951, Turkevich prepared metallic nanoparticles through a chemical mechanism for the first time. Many procedures for the synthesis of metallic nanomaterials exist, using both top-down and bottom-up approaches. However, as resources become scarcer and pollution increases, green methods have become more prominent, one such being biogenic synthesis as it takes advantage of biomolecules to replace chemical substances. In this work, silver nanoparticles were synthesized using Lactobacillus rhamnosus lysate to reduce silver nitrate, obtaining silver nanoparticles with a diameter close to 70 nm. The nanoparticles were characterized by Dynamic Light Scattering (DLS), X Ray Diffraction (XRD), UV-Vis Spectroscopy and Scanning Electron Microscopy (SEM). First, X-Ray Diffraction was used to determine the crystal structure and composition of AgNPs for comparison with previously reported studies. Henceforth, UV-Vis Spectroscopy showed an absorption peak at approximately 418 nm, which is within the UV absorption range for silver (400-460 nm). With these results, the nanoparticles were identified as AgNPs. Dynamic Light Scattering was used to optimize both the AgNPs size and size distribution (PDI) using a Factorial Design with three independent variables: reaction temperature, time and precursor (AgNO3) concentration. The optimal conditions for the formation of AgNPs were 60 °C, 60 minutes and 50 x 10-4 M AgNO3 concentration, obtaining an average particle size of 75.64 ± 3.04 nm and a PDI of 0.268 ± 0.014. In addition, zeta potential was measured to define the stability of AgNPs, with the previously mentioned optimized result having a Z-potential value of -36.07 ± 0.74. Scanning Electron Microscopy was used to confirm both the size and morphology of the AgNPs, observing particles of approximately the same sizes as the ones reported by DLS. Finally, the catalytic activity of AgNPs was tested with the degradation of methylene blue with NaBH4.