Biogenic Synthesis of Gold Nanoparticles with Cyanobacterium Lyngbya confervoides and In Vitro Antimicrobial Assessment.

Green nanotechnology is a suitable method, where natural reductants synthesize nanoparticles in an eco-friendly, safe, less hazardous, and less toxic manner. Nowadays, multidrug-resistant bacteria cause severe infections in public health; thus, new eco-friendly and less toxic antimicrobials are needed. An aliquot of 10 mL aqueous extract of nonnitrogen fixing cyanobacterium Lyngbya confervoides was added to a 40 mL 1 mm solution of HAuCl4 to obtain L. confervoides nanoparticles (Lc-AuNPs). Furthermore, the synthesized Lc-AuNPs were analyzed with UV-vis spectroscopy; the peak was obtained at 537 nm, at 350-650 nm. FTIR analysis at 4 cm-1 resolution at 450-4000 cm-1 showed the obtained bands at 2867.55, 2163.13, 2050.57, 1981.15, 1618.32, 1509.26, and 1011.64 cm-1. DLS analysis of Lc-AuNPs showed peaks between 10 and 100 d·nm and zeta potential values obtained between 50 and -50 mV. FESEM analysis of Lc-AuNPs confirmed the spherical-shaped nanoparticles within 100 nm size. EDX analysis of Lc-AuNPs presents the elements C, O, Au, Na, and K. Subsequently, the biosynthesized Lc-AuNPs were monitored against multidrug-resistant (MDR) pathogenic bacterial strains, Gram +ve Staphylococcus aureus and Streptococcus pyogenes and Gram -ve Escherichia coli and Acinetobacter baumannii, proving excellent activities with obtained zone of inhibition of 14, 16, 14, and 14 mm, respectively. Furthermore, Lc-AuNPs were tested against fungal strains Trichophyton rubrum and Candida tropicalis, which had zones of inhibition of 12 and 12 mm, respectively. The studied MIC values of Lc-AuNPs against bacteria S. aureus, S. pyogenes, E. coli, and A. baumannii were 100, 25, 100, and 50 μg/mL, respectively. Furthermore, the MIC values against fungal strains T. rubrum and C. tropicalis were 3.12 and 6.25 μg/mL, respectively. This revealed potent antimicrobial properties of Lc-AuNPs and could be used as future antibacterial agents and antifungals.