Ligand effect on controlling the synthesis of branched gold nanomaterials against fusarium wilt diseases

The widespread wilt disease caused by Fusarium solani spp is a pressing problem affecting crop production and intensive farming. Strategic biocontrol of Fusarium solani spp using phytochemical mediated nano-materials is eco-friendly compared to harsh synthetic fungicides. The present study demonstrates the comparative dose effects of QPABA-derived branched gold nanomaterial (AuNF) and quercetin-mediated spherical gold nanoparticles (s-AuNPs) against Fusarium solani spp. Quercetin-para aminobenzoic acid (QPABA) was synthesized using reductive amination by reacting para-aminobenzoic acid with quercetin in an eco-friendly solvent at 25 °C. The structure elucidation was confirmed using ¹H and ¹³C-NMR. TLC analysis showed that QPABA (R_f = 0.628) was more polar in water than quercetin (R_f = 0.714). The as-synthesized QPABA serves as a reducing and capping agent for the synthesis of gold nanoflowers (AuNFs) and gold nanostars (AuNSs). The UV-vis, XRD, and TEM confirmed the SPR peak of gold (550 nm) and gold element with a particle size distribution of 20-80 nm for the nanostars respectively. AuNFs exhibited a significant (P < 0.05) inhibitory effect against F. solani in a dose-dependent manner using Agar well diffusion. Nevertheless, spherical-AuNPs were not effective against F. solani. The inhibitory effect was influenced by the size, dose treatment, and particle shape. The minimum inhibitory concentration (MIC) value of AuNFs was 125.7 ± 0.22 μg mL⁻¹. Our results indicate that AuNFs show considerable antifungal activity against F. solani as compared to spherical AuNPs. This study shows a greener synthesis of gold anisotropic nanostructures using QPAB, which holds promise for the treatment of fungal pathogens impacting agricultural productivity.