Eco-friendly synthesis of Cucumis melo-mediated silver nanoparticles for antibacterial, heavy metal sensing, and photocatalytic applications

This study reports the green synthesis of silver nanoparticles (AgNPs) using an aqueous leaf extract of Cucumis melo var. agrestis (CMVA) as a natural reducing and stabilising agent under sunlight. The biosynthesized CMVA-AgNPs were characterised by UV–Vis spectroscopy, Fourier transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM), X-Ray Diffraction (XRD), energy-dispersive X-ray (EDX) analysis, zeta potential, and Dynamic Light Scattering (DLS) analyses, confirming their crystalline, spherical morphology with an average size of 72 nm and good colloidal stability (–25 mV) with a hydrodynamic diameter of 75.35 nm. FTIR revealed the involvement of key functional groups, such as O–H (alcohols/phenols), N–H (amines), C = O (carbonyls), C–O (esters/ethers), and C–H (alkanes), in the reduction and stabilisation of AgNPs. The AgNPs exhibited significant antibacterial activity against Escherichia coli , Listeria monocytogenes , Staphylococcus epidermidis , and Bordetella bronchiseptica , with inhibition zones of 15–26 mm and minimum inhibitory concentration (MIC) values ranging from 30 to 50 µg mL -1 . In colorimetric sensing assays, the CMVA-AgNPs demonstrated high selectivity and sensitivity toward Hg 2+ and Fe 3+ ions, with visible colour changes and detection limits in the micromolar range, even in the presence of competing cations and anions. Photocatalytic degradation studies further highlighted their efficiency in removing organic pollutants, achieving up to 95% degradation of methylene blue (MB), 57% of methyl orange (MO), and 90% of 4-nitrophenol (PNP) under sunlight irradiation. These findings establish CMVA-AgNPs as cost-effective, eco-friendly, and multifunctional nanomaterials with promising applications in heavy metal sensing, wastewater treatment, antimicrobial therapy, and environmental remediation.