Cellulose–Silver and Cellulose–Gold Bioactive Nanocomposites Obtained Using SCOBY Purified Membranes

The green synthesis of bioactive nanomaterials is becoming more attractive in various fields like biotechnology, pharmaceuticals, cosmeceuticals, etc. In this study, bacterial cellulose-silver and bacterial cellulose-gold bionanocomposites were obtained through an environmentally friendly and low-cost method without using additional reducing agents. In the first step, the bacterial cellulose, a byproduct from kombucha production using a symbiotic culture of bacteria and yeast (SCOBY), was purified using an alkaline solution. In the second step, the purified bacterial cellulose (SBC) was used to obtain silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) on the bacterial cellulose matrix, starting only from metal precursors in different media: water, black tea, and kombucha. Gold and silver nanoparticles were obtained on cellulose fibrils in all media, even in water, indicating the reducing role of cellulose. The morphology and structural features of the noble metal nanoparticles/bacterial cellulose nanocomposites (AgNPs/SBC and AuNPs/SBC) were investigated. Scanning electron microscopy (SEM) images show nanoparticles with an irregular shape with dimensions ranging from a few nanometers up to 70 nm, depending on the synthesis medium. TEM analysis revealed mostly quasi-spherical nanoparticles distributed along the surface of the cellulose fibers or within the interfibrillar pores. All nanoparticles are well crystallized and generally formed from more than two nanocrystallites, except AuNPs obtained in kombucha which are monocrystalline. XRD analysis shows the characteristic diffractograms of Iβ cellulose allomorphs and confirms the formation of crystalline AgNPs and AuNPs. The antioxidant capacity tests determined that the best activity was registered for the AgNPs/SBC composites obtained in kombucha and fresh black tea. The antimicrobial potential was evaluated against the Gram-negative bacteria <i>Escherichia coli</i> and the Gram-positive bacteria <i>Staphylococcus aureus</i> and <i>Listeria monocytogenes</i>. Cellulose-silver and cellulose-gold nanocomposites showed increased antimicrobial activity compared with raw SBC, especially in the case of kombucha medium for green synthesis. The highest antioxidant activity, determined by DPPH and ABTS assays, was obtained for AgNPs/SBC produced in kombucha and fresh black tea. Based on the results, cellulose-silver and cellulose-gold nanocomposites could be considered as bioactive materials for multiple practical applications, such as the medical field and food packaging.