Green Synthesis of AuNPs by Crocus caspius—Investigation of Catalytic Degradation of Organic Pollutants, Their Cytotoxicity, and Antimicrobial Activity

Biogenic methods are an effective alternative to chemical methods in the preparation of nanoparticles. Our study used Crocus caspius extract to synthesize gold nanoparticles (CC-AuNPs) in a green manner. The eco-friendly synthesis of AuNPs was conducted by optimizing the temperature and concentration of HAuCl4 and extract. Synthesized CC-AuNPs were characterized using TEM, SEM, EDX, XRD, FTIR, and UV–Vis spectroscopy. The prepared CC-AuNPs were detected with a size of around 22.66 ± 1.67 nm. The FT-IR analysis of the biomolecules involved in synthesizing CC-AuNPs was performed. Additionally, these biomolecules capped on the AuNPs were revealed by TG/DTA analysis. The EDX study demonstrated the existence of elemental gold. The biosynthesized CC-AuNPs were effectively applied as green catalysts to reduce three organic pollutant dyes—methyl orange (MO), methylene blue (MB), and 4-nitrophenol. In the biological evaluations, the free radical scavenging activity of the eco-friendly CC-AuNPs (DPPH assay) indicated an IC50 value of 29.22 ± 0.47 µg/mL. They displayed effective antibacterial activity against several bacterial strains. Their anticancer activity against AGS and MCF-7 cells showed IC50 concentrations at 48.2 µg/mL and 51.76 µg/mL, respectively. Furthermore, CC-AuNPs presented excellent antileishmanial activity (IC50 = 13.92 µg/mL). Therefore, the green AuNPs are efficient in biomedicine and nanobiotechnology.