INTRODUCTION
Nanotechnology has rapidly emerged as a leading field in science and technology, thanks to the ability to design and engineer innovative materials at the nanoscale [1]. At this scale, nanoparticles can exhibit chemical properties that differ fundamentally from those of their conventional (bulk) counterparts, even when composed of the same chemical constituents [2]. Among nanomaterials, metal oxide nanoparticles have garnered significant attention due to their selectivity, stability, and durability, as well as their relatively low toxicity compared to many organic compounds [3]. Nanoparticle size plays a pivotal role in determining their fundamental physical and chemical properties. Given these distinctive characteristics, they have attracted widespread interest for use in diverse applications, including medical diagnostics, catalytic processes, water purification, drug delivery systems, semiconductor devices, cosmetic formulations, solid oxide fuel cells, and sensing applications [4,5]. In particular, aluminum oxide nanoparticles have been used as adsorbents in heterogeneous catalysis, as abrasives, as reinforcing agents in metal-matrix composites, and as biomaterials [6,8]. Aluminum oxide nanoparticles are also used in significant applications within the ceramics industry [7]. Meanwhile, the increasing prevalence of microorganisms resistant to commonly used antibiotics has become a growing concern in recent years [9]. As particle size decreases from the micrometer to the nanometer range, the available surface area increases significantly. This high surface area to volume ratio, in addition to the unique physical and chemical properties of nanomaterials, has contributed to their emergence as promising antimicrobial agents [10]. The large contact area is expected to enhance interaction with bacterial cells, thus increasing the rate of bacterial elimination [11]. Moreover, the biological activity of nanoparticles can be influenced by the active chemical groups present on their surfaces; Consequently, both the type of metal oxide nanoparticles and their surface chemistry are important factors when evaluating their toxicity towards microorganisms [12]. Alumina nanoparticles are characterized by their thermodynamic stability across a wide temperature range. Their structure resembles that of corundum, wherein oxygen atoms are arranged in a hexagonal close-packed pattern, while aluminum ions occupy approximately (two, thirds) of the octahedral sites within the crystal lattice [13]. Based on the available literature, limited research has addressed the antibacterial properties of alumina nanoparticles; Therefore, this study was conducted to evaluate the antibacterial performance and minimum inhibitory concentration (MIC) of aluminum oxide (Al₂O₃) nanoparticles prepared via the co-precipitation method.

MATERIALS AND METHODS 
Preparation of alumina nanoparticles
Alumina nanoparticles were synthesized via the co-precipitation method, using aluminum sulfate and sodium hydroxide as starting materials. A 0.1 M aluminum sulfate solution was prepared by dissolving the required amount in distilled water with continuous magnetic stirring for one hour. After that, 0.2 M sodium hydroxide solution was added dropwise under constant stirring until a white gelatinous precipitate formed. The suspension was allowed to age overnight, after which the supernatant was carefully decanted. The resulting precipitate was washed several times with distilled water to remove any residual ions, and subsequently dried overnight at 80°C. Finally, the dried precipitate was calcined at an appropriate temperature to obtain crystalline alumina (Al₂O₃) nanoparticles as seen in Fig. 1.

Preparation of Bacterial Samples 
In this study, (Gram-positive) Staphylococcus aureus bacteria were obtained from the Contaminating Bacteria Laboratory of the Ministry of Science and Technology in Baghdad, Iraq. Using a sterile inoculation loop, a single colony from each bacterial strain was transferred into 10 mL of nutrient broth and incubated overnight at 37°C. Subsequently, the cultures were centrifuged at 6,000 RPM for 5 minutes to prepare bacterial suspensions, and the concentration of the Streptococcus (Gram-positive) suspension was adjusted to approximately 1–10 × 10⁸ colony-forming units per milliliter (cfu/mL). After removing the supernatant, the bacterial cells were resuspended in 500 µL of PBS (phosphate buffered saline) and centrifuged three times to remove any residual culture medium or cell debris [14]. After the final wash, the supernatant was removed, and the cells were resuspended in 50 µL of PBS, the suspension was then thoroughly mixed using a pipette to ensure a homogeneous distribution of cells prior to deposition onto the substrate. As seen in Fig. 2 schematic illustration of bacterial suspension preparation for antibacterial activity assay.

RESULTS AND DISCUSSION
X-ray diffraction result for Nano aluminum
In Fig. 3 Peaks located at approximately 38.5°, 44.7°, 65.1°, and 78.2° (2θ). These peaks are indexed to the (111), (200), (220), and (311) crystallographic planes, respectively, confirming the face-centered cubic (FCC) crystal structure of aluminum. The diffraction pattern is in good agreement with the standard ICDD PDF card No. 04-0787 for metallic aluminum. The high intensity and narrow peak widths indicate that the sample possesses good crystallinity and a well-ordered crystal lattice. Furthermore, no additional diffraction peaks corresponding to impurity phases or crystalline aluminum oxides are observed within the measured 2θ range, suggesting that the sample is predominantly composed of crystalline aluminum. The strongest diffraction peak appears at approximately 38.5°, corresponding to the (111) plane, which is the characteristic preferred reflection of FCC aluminum, while the remaining peaks exhibit the expected relative intensities, further confirming the phase purity and crystalline nature of the material. The obtained results were in good agreement with the calculated unit cell dimensions, where a= 0.5681 nm, b= 0.2890 nm, and c= 1.1776 nm [15-16].

TEM Analysis of Aluminum Nanoparticles
The TEM image of the aluminum sample reveals the presence of agglomerated nanoparticles with irregular to nearly spherical morphology. The particles are clustered together, forming larger aggregates, which is commonly attributed to the high surface energy of nanosized aluminum particles. Although individual particles can be distinguished in some regions, the strong agglomeration makes precise particle size determination difficult from this image alone. No rod-like or plate-like structures are observed, indicating that the particles predominantly exhibit a quasi-spherical morphology. The observed contrast is consistent with crystalline metallic particles distributed in aggregated domains. These TEM observations in Fig. 4 are in good agreement with the XRD results, which exhibited sharp diffraction peaks at 2θ values of approximately 38.5°, 44.7°, 65.1°, and 78.2°, corresponding to the (111), (200), (220), and (311) planes of face-centered cubic (FCC) aluminum (ICDD PDF No. 04-0787). The sharp diffraction peaks confirm the crystalline nature of the aluminum particles observed in the TEM image, while the absence of additional diffraction peaks in the XRD pattern supports the predominance of a single crystalline aluminum phase. Therefore, the combined TEM and XRD analyses indicate that the sample consists of crystalline aluminum nanoparticles with an aggregated morphology [17-19].

The UV–Vis absorption spectrum of the synthesized alumina nanoparticles
The UV–Vis absorption spectrum of the synthesized alumina nanoparticles exhibits strong absorption in the ultraviolet region, with the highest absorption intensity observed at wavelengths below approximately 220 nm. A sharp decrease in absorbance is observed as the wavelength increases, followed by a nearly constant and very low absorption throughout the visible region (300–1100 nm) Fig. 4. This optical behavior is characteristic of alumina, reflecting its wide band gap and high transparency in the visible range. The absence of significant absorption peaks in the visible region indicates that no detectable impurity-related electronic transitions are present. These results Fig. 5 are consistent with the XRD analysis, which confirmed the formation of crystalline Al₂O₃ without detectable secondary crystalline phases, suggesting that the synthesized nanoparticles possess high structural purity and suitable optical properties for ultraviolet and optoelectronic applications [20].

Antibacterial activity of the Al Nano powder
The antibacterial activity of nanomaterial against Staphylococcus aureus as seen in Fig. 6 was evaluated using the agar diffusion method. As shown in the figure, the control (A) exhibited little or no inhibition zone, indicating the absence of antibacterial activity. The treated samples produced concentration-dependent zones of inhibition; the lower concentration (12.5%, B) exhibited a clear zone of inhibition, whereas the 25% concentration (C) showed moderate antibacterial activity. At a concentration of 50% (D), the zone of inhibition was larger than that observed with sample C, indicating improved antibacterial activity. The 100% concentration (E) yielded the widest zone of inhibition, demonstrating the strongest effect against S. aureus. Overall, the results indicate that the antibacterial activity of the nanomaterial increased with increasing concentration, suggesting that the inhibition of bacterial growth is concentration-dependent [21,22].

CONCLUSION 
Aluminum oxide nanoparticles were successfully prepared via the co-precipitation method, using aluminum sulfate and sodium hydroxide as starting materials. X-ray diffraction analysis confirmed the crystalline nature of the Al₂O₃ nanoparticles, while transmission electron microscopy observations confirmed their nanoscale morphology, noting some particle agglomerationAntibacterial testing against *Staphylococcus aureus* demonstrated that the inhibitory effect increases with nanoparticle concentration, with the 100% concentration producing the largest zone of inhibition. These results indicate that the synthesized aluminum oxide nanoparticles exhibit activity against Gram-positive bacteria and hold promising potential for biomedical and antimicrobial applications. Further studies are required to evaluate their biocompatibility, cytotoxicity, and efficacy against a broader range of pathogenic microorganisms.

CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.