Stabilization of gold nanoparticles (Rp@AuNPs) by <i>Ruellia patula</i> extract for broad-spectrum antimicrobial, anti-inflammatory and anti-diabetic activities

Gold nanoparticles (AuNPs) have gained considerable attention in biomedical, environmental, and pharmaceutical applications due to their distinct physiochemical attributes. Plant-mediated green synthesis of AuNPs provides low-cost and pollution-free alternatives to traditional chemical synthesis. Leaf extract of <i>Ruellia patula</i> (Rp) was utilized as bioreduction agent and stabilizer for the synthesis of Rp@AuNPs. Spectroscopic peak at 520 nm affirmed the synthesis of Rp@AuNPs, validated using surface plasmon resonance. XRD patterns confirmed the crystallinity of the resultant nanoparticles, while electron microscopic images analyzed their size distribution and morphology, which ranged from 22.47 to 84.57 nm. Subsequently, FTIR analysis denoted the chemically active biomolecules for nanoparticle reduction and stabilization. Large inhibition zones indicated that biosynthesized Rp@AuNPs exhibited significant antibacterial activity toward <i>Streptococcus pyogenes</i> and <i>Pseudomonas aeruginosa</i>. In addition to demonstrating intense antioxidant and antidiabetic activities, the Rp@AuNPs exhibited anti-inflammatory activity by protein denaturation inhibition and HRBC membrane stability assays. The synthesized Rp@AuNPs ranged from 22.47 to 84.57 nm in size and exhibited antibacterial activity with inhibition zones up to 17 mm, antioxidant activity with DPPH and ABTS scavenging efficiencies of 86.7% and 82.9%, respectively, anti-inflammatory activity with 78.5% protein denaturation inhibition, and antidiabetic activity showing IC₅₀ values of 55.6 µg/mL (α-amylase) and 50.8 µg/mL (α-glucosidase).