Green synthesis of Ag or Au nanoparticles for antimicrobial applications using wild consortia of SCOBY-based membranes

The green synthesis of bioactive nanoparticles (NPs) is biologically safe, cost-effective, and environment-friendly, and is becoming more attractive in various fields: the food industry, biotechnology, materials science, pharmaceuticals, and cosmeceuticals. Kombucha culture (named SCOBY—Symbiotic Culture of Bacteria and Yeasts) is a wild consortium of microorganisms naturally immobilized in a nanocellulose membrane. In this study, SCOBY-based membranes decorated with gold NPs (AuNPs) or silver NPs (AgNPs) were produced through an eco-friendly process. In the first stage, the microbial consortium immobilized in a nanocellulose membrane was grown by the fermentation of a black tea-based medium. AgNP and AuNP deposition on the SCOBY nanocellulose membrane (SNM) was achieved using only the washed, dried, and finely ground SNM and metal precursors. The biosynthesized AuNPs/SNM and AgNPs/SNM were characterized by Scanning Electron Microscopy (SEM) coupled with Energy-Dispersive Spectroscopy (EDS), X-ray diffraction (XRD), and Fourier-Transform Infrared (FTIR) Spectroscopy. SEM images show cellulose fibrils and the successful incorporation of Ag nanoparticles with an average size of 50 nm and Au nanoparticles (30 nm) into SNM. In XRD, the characteristic diffractograms of Iα and Iβ cellulose allomorphs appear and the representative patterns confirm the formation of AgNPs and AuNPs. The antimicrobial potential of the SNM enriched with nanoparticles was evaluated by the well-diffusion technique against the Gram-negative bacteria Escherichia coli and the Gram-positive bacteria Staphylococcus aureus. The metal-decorated SNM showed good antimicrobial potential, and the results highlight the increased antimicrobial performance of AuNPs/SNM and AgNPs/SNM compared to raw SNM. The results recommend Ag-decorated SNM (Ag-SNMs) and Au-decorated SNM (Au-SNMs) for multiple practical applications such as medical and food packaging fields. The antioxidant effect was determined by DPPH and ABTS tests. In the DPPH assay, the Au-NPs and Ag-NPs showed a higher antioxidant activity.