A new study from researchers at the University of Baghdad has combined pulsed laser ablation with plant-based chemistry to produce copper oxide nanoparticles with controlled dimensions, a biological surface coating and measurable antibacterial activity. The approach, reported in Applied Nanoscience, uses Hibiscus sabdariffa extract during the laser fabrication process, offering a route toward nanomaterials that reduces reliance on conventional chemical reagents. The researchers compared two forms of CuO nanoparticles: particles generated by pulsed laser ablation in deionized water alone and particles produced when the same process was assisted by the plant extract. Their results suggest that a simple change in the liquid surrounding the target can significantly influence the size, uniformity and surface chemistry of the final nanomaterial.
Pulsed laser ablation in liquid, commonly known as PLAL, is a physical synthesis technique in which a high-energy laser is directed at a solid target submerged in a liquid. Each laser pulse rapidly heats and vaporizes a microscopic region of the target, creating a short-lived plasma plume composed of atoms, ions and clusters. As the plume expands into the surrounding liquid, it cools and condenses, generating nanoparticles without the need for reducing agents, organic solvents or complex chemical precursors. The process is attractive because the material is produced directly from a solid source and can yield relatively pure colloidal nanoparticles. However, particle growth and aggregation can be difficult to control. The Baghdad team investigated whether molecules naturally present in Hibiscus sabdariffa could help regulate these processes while also adding biological functionality to the particle surface.
The choice of Hibiscus sabdariffa, commonly known as roselle, reflects the growing interest in plant extracts as multifunctional components of nanomaterial production. Plant tissues contain polyphenols, flavonoids, organic acids, pigments, sugars and other compounds capable of interacting with newly formed inorganic surfaces. During laser ablation, these molecules can adsorb onto nascent CuO particles, acting as capping agents that limit uncontrolled coalescence. A capping layer can also improve colloidal stability by creating steric or electrostatic barriers between particles, preventing them from sticking together. In addition, the immobilized phytochemicals may modify surface charge, wettability and chemical reactivity. These changes are important in biological applications because antibacterial performance depends not only on the chemical identity of a nanoparticle but also on its size, aggregation state and interface with microbial cells.
Structural analysis confirmed that both experimental routes produced crystalline copper oxide. X-ray diffraction, or XRD, is used to identify the ordered atomic arrangement within a solid by measuring how the material diffracts incident X-rays. The resulting diffraction pattern provides a fingerprint of the crystal phase and can also be used to estimate crystallite dimensions through peak broadening. In this study, the analysis indicated the formation of nanosized CuO in both the extract-free and plant-assisted samples. The laser-generated particles were therefore not simply amorphous copper-containing fragments; they possessed the crystalline structure expected for copper oxide. This distinction matters because crystal phase can influence optical absorption, defect chemistry, catalytic behavior and the release of copper-related species in aqueous environments.
The most visible difference emerged in the morphology and particle-size distribution. Electron microscopy showed that the nanoparticles produced in deionized water had an average size of approximately 23.0 ± 18.9 nanometers and a relatively broad distribution. The large standard deviation indicates substantial variation around the mean, suggesting that the sample contained particles of markedly different dimensions. In contrast, the green-assisted material formed smaller, more uniform nanobead-like structures with an average diameter of about 16.6 ± 10.5 nanometers. Although the spread remains considerable, the lower average size and altered morphology point to a regulatory effect from the extract. During and after laser-induced nucleation, phytochemicals may bind to active growth sites, slowing the addition of copper and oxygen species to particle surfaces. They may also hinder collisions that would otherwise produce larger aggregates.
This size reduction is more than a cosmetic improvement. Nanoparticles possess a high surface-area-to-volume ratio, and that ratio rises as the particles become smaller. A greater fraction of atoms is consequently located at or near the surface, where they can interact with water, oxygen, organic molecules and bacterial membranes. Smaller particles can remain suspended more effectively when protected by a suitable capping layer, increasing the area available for contact with microorganisms. At the same time, size alone does not determine biological performance. A dense organic coating can shield reactive sites or slow the release of copper ions, while an unstable suspension can produce aggregates that behave like much larger particles. The study’s comparison illustrates why nanoparticle synthesis must be evaluated as a complete system involving core composition, surface chemistry, dispersion behavior and biological environment.
Energy-dispersive X-ray spectroscopy, or EDS, provided additional evidence about the composition of the products. The extract-free material was dominated by copper and oxygen, as expected for CuO nanoparticles. The green-assisted particles also contained copper and oxygen, but their spectra revealed contributions associated with biological material derived from the plant extract. EDS cannot identify every individual organic molecule, and its elemental signals should not be interpreted as a complete chemical map of the capping layer. Nevertheless, the detection of additional biological components supports the conclusion that plant-derived substances remained associated with the nanoparticle surfaces after synthesis. These molecules may be responsible for the differences in particle size, morphology, stability and antibacterial behavior observed between the two preparation methods.
The antibacterial tests focused on Staphylococcus aureus, a Gram-positive bacterium, and Klebsiella pneumoniae, a Gram-negative bacterium. In a standard zone-of-inhibition assay, a suspension or dispersion containing an antimicrobial substance is placed near a bacterial culture, and the clear region surrounding it is measured after incubation. The extract-free CuO nanoparticles produced inhibition zones of 12.3 ± 0.6 millimeters against both organisms. The plant-assisted nanoparticles generated zones of 9.3 ± 0.6 millimeters against S. aureus and 9.0 ± 1.0 millimeters against K. pneumoniae. These measurements show that both materials inhibited bacterial growth under the test conditions, although the extract-free particles produced larger visible zones in this particular assay. The result emphasizes that “green” synthesis does not automatically mean stronger antibacterial action; surface coatings can alter how quickly active species diffuse through the culture medium and reach bacterial cells.
Copper oxide nanoparticles are thought to attack bacteria through several interacting mechanisms. Their surfaces can generate reactive oxygen species, including superoxide-related and hydroxyl-type oxidants, especially under conditions that promote electron–hole or defect-mediated reactions. These reactive molecules can damage membrane lipids, proteins and nucleic acids. CuO particles may also attach directly to bacterial envelopes, disturb membrane integrity and promote the release of copper ions. Once inside or near the cell, copper can interfere with enzymes and redox balance. The exact contribution of each pathway depends on particle size, oxidation state, dissolved oxygen, pH, illumination, aggregation and the composition of the surrounding medium. In the green-assisted samples, plant molecules could contribute their own antimicrobial effects, but they could also reduce direct contact between the inorganic core and the bacterial membrane. The authors associate the observed activity with the combined influence of CuO and surface-bound phytochemicals.
The researchers present the method as a sustainable alternative for producing bioactive nanomaterials because PLAL can avoid many hazardous chemical reagents and the plant extract is renewable and comparatively accessible. The process also offers a way to tune particle properties through laser parameters and liquid composition rather than relying exclusively on synthetic surfactants. Still, sustainability must be assessed across the full production cycle. Energy consumption during laser operation, extract preparation, purification, scale-up and waste management will determine whether the laboratory method remains environmentally advantageous at industrial volume. Before biomedical or environmental deployment, the nanoparticles will also require rigorous testing for cytotoxicity, copper release, long-term colloidal stability, ecotoxicity and performance in complex biological fluids. Even with these questions outstanding, the study demonstrates a useful principle: pairing the precision of laser ablation with the molecular diversity of plants can create CuO nanoparticles whose structure and interface are more controllable than those produced by either strategy alone. The work adds to a rapidly expanding field in which sustainable nanotechnology is being developed not simply to reduce chemical waste, but to engineer materials with deliberately designed biological behavior.
Subject of Research: Green-assisted pulsed laser ablation synthesis of copper oxide nanoparticles and their antibacterial properties
Article Title: Green-assisted pulsed laser ablation for the sustainable synthesis of CUO nanoparticles with antibacterial properties
Article References: Alwan, F. J., Majeed, N. F., Merzah, Z. F., et al. “Green-assisted pulsed laser ablation for the sustainable synthesis of CUO nanoparticles with antibacterial properties.” Applied Nanoscience 16, Article 6 (2026). Published 18 December 2025. [rule_3]
Image Credits: AI Generated
DOI: 10.1007/s13204-025-03140-8 [rule_4]
Keywords: CuO nanoparticles, pulsed laser ablation in liquid, green synthesis, Hibiscus sabdariffa, phytochemicals, antibacterial activity, Staphylococcus aureus, Klebsiella pneumoniae
Tags: antibacterial copper oxide nanoparticlesbio-inspired approaches for sustainable nanomaterialsenvironmentally friendly nanomaterialsgreen chemistry in nanoparticle synthesisGreen-assisted pulsed laser ablationHibiscus sabdariffa in nanofabricationlaser ablation in liquid for nanoparticle productionlaser-based nanomaterial manufacturingnanotechnology for antimicrobial applicationsplant-based nanomaterial synthesissurface chemistry modification of CuO nanoparticlessustainable copper oxide nanoparticles
