Green synthesis of gold nanoparticles using Turnera diffusa Willd enhanced antimicrobial properties and immune response in Longfin yellowtail leukocytes

Plant‐mediated nanoparticle synthesis is an eco‐friendly method designed to reduce toxicity. This research reports the effects of gold nanoparticle green synthesis on immune modulation for the first time, using aqueous extract from Turnera diffusa . First, the chemical composition showed that T. diffussa is abundant in compounds, such as oplopanone, γ‐eudesmol, hydroquinone‐β‐ d ‐glucoside (arbutin) and inositol. The synthesized gold nanoparticles (AuNPDam) were confirmed by ultraviolet visible (UV‐Vis) spectrophotometry; the micro‐graphical analysis confirmed the average size that was estimated about 24 nm, which were mostly spherical in shape. The Fourier transform infrared spectroscopy (FTIR) technique helped to confirm the functional groups of the synthesized AuNPDam. Its antioxidant capability was analysed using 2,2‐diphenyl‐1‐picrylhydarzyl (DPPH), superoxide radical scavenging and fluorescence recovery after photobleaching (FRAP) methods. These results indicated a worthy antioxidant activity. The synthesized AuNPDam showed strong antibacterial activity against Vibrio parahaemolyticus and Aeromonas hydrophila . Interestingly, AuNPDam were nontoxic to Longfin yellowtail head kidney leukocytes after 24 h. The phagocytosis activity, production of reactive oxygen species and nitric oxide were also enhanced in leukocytes treated with AuNPDam. Overall, the results suggested that AuNPDam is non‐cytotoxic, displays strong bactericidal activity and has therapeutic properties by enhancing the immune system.