Evaluating the Synergistic Antioxidant, Anti-microbial and Adsorbent Potential of Andrographis Paniculata Extract and Gold Nanoparticles

The present study introduces a minimalistic and cost-effective approach to synthesising Gold nanoparticles (AuNPs) using aqueous leaf extracts of Andrographis paniculata. In this synthesis, bioactive metabolites in the leaf extract act as reducing agents, converting Au³⁺ ions to metallic Au⁰, while proteins in the extract form a stabilising layer around the nanoparticles to prevent agglomeration and maintain particle size stability. The synthesised AuNPs were systematically characterised using a range of analytical techniques. UV-visible spectroscopy verified the presence of surface plasmon resonance, Fourier-transform infrared (FTIR) spectroscopy identified key functional groups, X-ray diffraction (XRD) revealed high crystallinity, and Transmission Electron Microscopy (TEM) indicated particle sizes ranging from approximately 4-15 nm. Additionally, Energy Dispersive X-ray (EDX) analysis confirmed the elemental composition of the nanoparticles. The biological efficacy of the synthesised AuNPs was rigorously evaluated. Antioxidant activity, assessed via DPPH and ABTS assays, showed notable results, with inhibition rates of 87.35% and 75% at a sample concentration of 100 µg/mL, respectively. In vitro cytotoxicity studies on Vero cells demonstrated a significant reduction in cell viability, reaching a minimum of 18.22% at the highest tested concentration of 100 µg/mL. Antimicrobial assays indicated strong activity against Salmonella typhii and Escherichia coli, with comparatively lower efficacy against Pseudomonas aeruginosa and Bacillus cereus. Furthermore, adsorption studies showed the AuNPs' high efficiency in removing 99% of crystal violet dye (500 mg/L) within 30 min under optimised conditions (pH 4.5, temperature 33 °C, and an AuNP dosage of 200 mg/L). This comprehensive analysis indicates that the synthesised AuNPs from A. paniculata exhibit promising properties for applications in biomedicine and wastewater treatment.