Sunlight-assisted synthesis of bimetallic silver–copper nanoparticles using peanut shell extract and its reusable activity against drug-resistant bacteria

Abstract

New antibacterial compounds are needed to tackle bacteria that are resistant to antibiotics. Herein, we report an environmentally benign method for synthesizing bimetallic silver–copper nanoparticles (Ag–Cu NPs) using sunlight and aqueous peanut shell extract. Phytochemical analysis discloses that the aqueous extract contains diverse phytochemicals, including flavonoids, amino acids, tannins, alkaloids, and saponins, which aid in sunlight harvesting to reduce and stabilize metal precursors to NPs. The formation of bimetallic Ag–Cu NPs was confirmed by UV-visible spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and electron dispersive X-ray spectroscopy (EDX). Fourier transform infrared spectroscopy (FTIR) and XPS analysis revealed that the phytochemicals present in the extract stabilize the NPs. Transmission electron microscopy showed that the NPs are spherical with an average size of 29 ± 14 nm. Ag–Cu NPs were effective against Escherichia coli, Pseudomonas aeruginosa, carbapenem-resistant Acinetobacter baumannii, Staphylococcus aureus, Enterococcus faecalis and methicillin-resistant Staphylococcus aureus at MIC values of 156.3, 156.3, 156.3, 312.5, 156.5, and 312.5 μg mL⁻¹, respectively. The colony count method and time-kill curve analysis reveal that the NPs effectively inhibited bacterial growth from 0.25× MIC and showed a significant reduction in 30 min. Interestingly, the NPs antibacterial capabilities last beyond their initial use because they are washable and reusable. Mechanistic studies revealed that the NPs kill bacteria by damaging the membranes and producing excess reactive oxygen species to oxidize the membrane lipids. The findings showed the potential of agro-waste to prepare biogenic Ag–Cu NPs to combat drug-resistant bacteria.