Structural and antibacterial evaluation of copper, silver, and bimetallic silver/copper nanoalloys synthesized in chitosan biopolymer

Abstract

Silver nanoparticles (AgNP) have been used as an alternative to microbial resistance. Nevertheless, AgNP high cost and moderate toxicity to humans limit their use. Copper nanoparticles (CuNP) emerge as an alternative, but their fast oxidation hampers large-scale use. In this scenario, this work propose the synthesis optimization of Ag, Cu, and bimetallic Ag/Cu nanoparticles in a chitosan aqueous solution using factorial design statistics. UV-Vis spectroscopy, zetasizer, and transmission electron microscopy (TEM) measurements demonstrated that the optimized synthetic procedure formed highly stable and monodisperse nanoparticles. X-ray diffraction (XRD) confirmed the nanoparticle's crystalline structure and indicated the presence of an oxide state in CuNP. In addition, X-ray photoelectron spectroscopy (XPS) measurements confirmed that this oxidation occurs at the CuNP surface level. Considering Ag/CuNP, Rietveld refinement of XRD diffractogram demonstrates the formation of an unusual and novel Ag/Cu nanoalloy structure, which was possible due to the metallic ion chelation to chitosan nitrogens before and during nanoparticle growth. In addition, silver presence in the nanoalloy inhibited copper oxidation through an electromigration mechanism. Comparing CuNP, AgNP, and Ag/CuNP, it was possible to reveal the microbicide abilities of the nanoparticles against both Gram-positive and Gram-negative bacteria, emphasizing that the Ag/Cu nanoalloy is a viable option due its high antimicrobial activity and colloidal stability. Therefore, the rational design allowed the synthesis of highly stable NP in the chitosan matrix which exhibited strong antimicrobial activity, indicating that Ag/Cu nanoalloys can act as the next-generation nanomaterials for pathogenic microorganism inactivation.

Keywords

• Silver nanoparticles
• Copper nanoparticles
• Chitosan
• Bacteria inactivation