Biosynthesized silver nanoparticles (AgNPs) are widely used in varied applications, which are morphology dependent. Consequently, a morphology-controlled synthesis is mandatory. Although there are several studies focused on the plant extract-based biosynthesis of metallic nanoparticles, the use of extracts obtained from agro-wastes is scant. Furthermore, information regarding morphology modification through the use of additional agents is even more scarce. Thus, in this study, AgNPs were synthesized using a malt extract (ME) obtained from an artisanal beer brewing process residue. Additionally, sodium chloride (NaCl), gum arabic (GA), and talc (T) were used in an attempt to modify the morphology of AgNPs. XRD, DLS, SEM, and TEM results demonstrate that stable AgNPs of different sizes and shapes were synthesized. FTIR, HPLC analysis, and the quantification of total proteins, free amino acids, reducing sugars, and total polyphenols before and after AgNPs synthesis showed that ME biomolecules allowed them to act as a source of reducing and stabilizing agents. Therefore, this study provides evidence that ME can be successfully used to biosynthesize AgNPs. Additionally, the antibacterial activity of AgNPs against Gram-negative and Gram-positive bacteria was evaluated. Results indicate that AgNPs show a higher antibacterial activity against Gram-positive bacteria.

This work reports the biosynthesis of silver nanoparticles (AgNPs) using an autoclave method with Tagetes erecta extract (TEE) as a source of reducing agents, silver nitrate (AgNO₃) as the metal precursor, and a nucleating agent (i.e., sodium chloride [S]) or a structure director agent (i.e., gum Arabic [G] or hydrous magnesium silicate/talc powder [T]) to tailor the morphology of AgNPs. Since the properties and potential applications of AgNPs depend on their size and shape, these additives were employed to achieve morphological control. Phytochemical screening tests and UPCL-Qtof-MS/MS profiling of TEE were performed to identify the compounds present in the extract, indicating that highly polar phenolic compounds such as saponins, tannins, and flavonoids are present in TEE, allowing it to act as a source of reducing/stabilizing agents. The biosynthesized AgNPs exhibited different morphologies (i.e., spheres, rods, ribbons, and wires) depending on the modifying agent used (i.e., S, G, or T). Characterization techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis), and X-ray diffraction (XRD) confirmed the successful use of S, G, and T in modulating AgNP morphology. The results of the antibacterial activity evaluation demonstrated that both TEE and AgNPs possess bacteriostatic activity against Escherichia coli and Enterococcus faecalis, with the use of S as a nucleating agent increasing the inhibitory effect of AgNPs.