Introduction

Healthcare-associated infections (HAIs) remain one of the most significant global public health challenges. These infections are commonly acquired in hospitals, clinics, and healthcare environments, often appearing within 48 hours of treatment or even several weeks after patient discharge. According to the World Health Organization, microbial infections are responsible for hundreds of thousands of deaths worldwide every year. The increasing spread of multidrug-resistant microorganisms has intensified the need for innovative antimicrobial materials capable of reducing contamination and limiting pathogen transmission.

Textile materials are particularly vulnerable to microbial growth because their porous and hydrophilic structure can retain moisture, oxygen, organic residues, and nutrients. These conditions create a favorable environment for bacteria, fungi, and viruses to survive and proliferate. Fabrics used in hospitals, sportswear, underwear, footwear, and protective clothing are constantly exposed to biological contaminants such as sweat, blood, and body fluids. As a result, contaminated textiles can become sources of cross-transmission and secondary infections. Certain microorganisms can remain viable on fabric surfaces for extended periods, significantly increasing the risk of disease spread in medical and public environments.

To address these challenges, the textile industry has increasingly focused on the development of antimicrobial fabrics using advanced nanotechnology approaches. Nanotechnology enables the production of multifunctional textiles with enhanced physical, chemical, and biological properties. These functional fabrics can provide ultraviolet protection, antimicrobial and antifungal activity, antiviral performance, self-cleaning capability, odor control, and improved durability. Such materials have applications in healthcare products, wound dressings, sportswear, protective garments, shoe linings, and food packaging systems.

Among the different antimicrobial agents used for textile finishing, metal and metal oxide nanoparticles have attracted considerable attention. Materials such as copper, silver, iron oxide, and zinc oxide have demonstrated strong antimicrobial properties. However, zinc oxide nanoparticles (ZnO NPs) are particularly promising because of their excellent chemical stability, low toxicity, high biocompatibility, durability, and reduced tendency to induce microbial resistance. ZnO nanoparticles exhibit effective antibacterial, antifungal, and antiviral activity against a broad range of microorganisms. In addition, ZnO is environmentally friendly, highly degradable, and compatible with textile dyeing processes, making it highly suitable for large-scale industrial textile applications.

ZnO nanoparticles can act as both bacteriostatic and bactericidal agents. Their antimicrobial performance is associated with several mechanisms, including the production of reactive oxygen species, disruption of bacterial membranes, release of zinc ions, and direct interaction with microbial cell walls. These mechanisms can damage cellular structures, alter metabolic activity, and ultimately lead to microbial cell death. Because microbial resistance to traditional antibiotics continues to increase, ZnO nanoparticles represent an important alternative for the development of next-generation antimicrobial textiles.

Several synthesis routes have been proposed for producing ZnO nanoparticles, but the sol gel method stands out because of its simplicity, reproducibility, low production cost, and scalability. This technique enables nanoparticle synthesis at relatively low temperatures while maintaining good control over particle morphology and crystallinity. The classical sol–gel approach introduced for ZnO nanoparticle production demonstrated the ability to generate extremely small particles in the nanometer range. However, one of the main limitations of early synthesis methods was the poor stability and dispersion of ZnO nanoparticles in aqueous media.

To overcome this limitation, researchers have explored the use of organosilane modifiers capable of improving nanoparticle dispersion and stability. Organosilanes such as glycidyloxypropyl trimethoxysilane (GPTMS) can create protective surface layers around ZnO nanoparticles, allowing stable dispersion in hydrophilic environments while reducing particle agglomeration. Surface modification also contributes to maintaining very small nanoparticle sizes, which is essential for maximizing antimicrobial performance.

Nanoparticle size plays a critical role in determining antibacterial efficiency. Studies have consistently shown that smaller ZnO nanoparticles exhibit stronger antimicrobial activity than larger particles. Reducing nanoparticle diameter increases the surface area available for interaction with microorganisms and enhances penetration into bacterial membranes. Nanoparticles smaller than 10 nm are particularly effective because they can interact more efficiently with microbial cells and may even penetrate cellular structures. In contrast, larger particles generally show reduced antimicrobial activity and lower adhesion stability on textile fibers.

The durability of antimicrobial coatings during washing is another essential factor for practical textile applications. Many previously developed antimicrobial fabrics demonstrated initial antibacterial activity but lost effectiveness after repeated washing cycles due to nanoparticle detachment from textile surfaces. Smaller ZnO nanoparticles tend to exhibit stronger adhesion to textile fibers because they can penetrate deeper into the fiber structure, resulting in improved washing resistance and longer-lasting antimicrobial properties.

Despite significant progress in antimicrobial textile research, studies involving ZnO nanoparticles smaller than 10 nm incorporated into fabrics with long-term washing durability remain limited. Furthermore, the influence of textile treatments such as dyeing and fabric softeners on nanoparticle adhesion and antimicrobial efficiency has not been extensively investigated.

In this study, ultra-small ZnO nanoparticles with an average diameter of approximately 5 nm were synthesized using a modified sol–gel process and incorporated into polyamide fabrics through a simple and sustainable immersion technique. The work focused on evaluating the antibacterial activity, structural stability, and washing durability of fabrics subjected to different textile treatments, including dyed and undyed materials as well as fabrics with or without softener treatment. Antibacterial performance was investigated against both Gram-positive and Gram-negative bacterial strains before and after multiple washing cycles.

The developed approach offers several important advantages, including low production cost, environmentally friendly processing, easy scalability, and excellent long-term antibacterial activity. The results demonstrate the strong potential of ZnO nanoparticle-functionalized polyamide fabrics for applications in healthcare, hygiene products, sportswear, and protective textiles designed to reduce microbial proliferation and cross-contamination in different environments.

Experimental Procedure

Materials

The study utilized zinc acetate dihydrate as the zinc precursor and lithium hydroxide monohydrate as the hydrolysis agent for ZnO nanoparticle synthesis. Absolute ethanol was used as the solvent, while GPTMS acted as the surface-modifying organosilane compound. Polyamide fabrics containing elastane were selected as the textile substrate. Microbiological analyses were performed using Mueller–Hinton culture media and standard bacterial strains.

Synthesis of ZnO Nanoparticles

ZnO nanoparticles were synthesized using a modified sol–gel method. Initially, zinc acetate was dissolved in ethanol and heated under reflux conditions to form a stable precursor solution. After cooling, lithium hydroxide was added to initiate hydrolysis and condensation reactions, leading to ZnO nanoparticle formation.

The nanoparticle suspensions were exposed to ultrasonic treatment for different reaction durations, including 1 hour, 3 hours, and 24 hours. Surface modification was then performed using GPTMS to improve nanoparticle stability and facilitate water dispersion. The modified nanoparticles were centrifuged, dried, and subsequently dispersed in water to obtain stable colloidal suspensions suitable for textile impregnation.

Fabric Impregnation Process

ZnO nanoparticles were incorporated into polyamide fabrics using an immersion-based impregnation technique. Standardized fabric samples were immersed in aqueous nanoparticle dispersions under controlled agitation and temperature conditions. Different textile treatments were evaluated, including:

  • Dyed and undyed polyamide fabrics
  • Fabrics with softener treatment
  • Fabrics without softener treatment

This approach enabled the investigation of how textile finishing conditions influence nanoparticle adhesion and antibacterial performance.

Characterization Techniques

Several analytical methods were used to evaluate nanoparticle synthesis and fabric modification:

Antibacterial Evaluation

The antibacterial activity of the treated fabrics was evaluated using the agar diffusion method against:

  • Staphylococcus aureus
  • Escherichia coli

The inhibition zones formed around the textile samples were measured before washing and after multiple washing cycles to evaluate long-term antibacterial durability.

Results 

The ZnO nanoparticles synthesized at different reaction times exhibited very similar particle sizes, remaining close to 5 nm in diameter. This confirms that prolonged synthesis times were not necessary to obtain ultra-small nanoparticles. The small nanoparticle size is particularly beneficial because reduced dimensions significantly improve antibacterial efficiency.

XRD analysis confirmed that the synthesized nanoparticles possessed the characteristic hexagonal wurtzite crystalline structure of ZnO. After impregnation into polyamide fabrics, the characteristic ZnO diffraction peaks remained visible, demonstrating successful nanoparticle incorporation without structural degradation.

FTIR analysis further confirmed the presence of ZnO nanoparticles on the textile surface through the appearance of Zn–O vibrational bands absent in untreated fabrics. SEM images showed that untreated fibers possessed smooth surfaces, whereas treated fabrics displayed rougher textures with nanoparticle agglomerates distributed along the fibers. EDS analysis verified the presence of zinc and oxygen elements, providing additional confirmation of ZnO nanoparticle deposition.

The antibacterial tests demonstrated strong activity against both bacterial strains. However, the treated fabrics showed greater effectiveness against Staphylococcus aureus compared with Escherichia coli. This behavior agrees with previous studies indicating that Gram-positive bacteria are generally more susceptible to ZnO nanoparticle-based antimicrobial systems.

One of the most important findings was the excellent washing durability of the antimicrobial treatment. The fabrics maintained strong antibacterial activity even after 10 and 20 washing cycles. This durability is likely associated with the extremely small nanoparticle size and the effective surface modification process, which improved nanoparticle adhesion within the textile structure.

The study also demonstrated that fabric dyeing and softener treatments did not significantly reduce antibacterial performance. This result highlights the versatility of the developed process and its compatibility with conventional textile finishing procedures.

Conclusion

This study demonstrated the successful development of sustainable antibacterial polyamide fabrics containing ultra-small ZnO nanoparticles synthesized through a low-cost sol–gel process. The nanoparticles exhibited excellent structural stability, strong antibacterial activity, and remarkable washing durability.

The incorporation of approximately 5 nm ZnO nanoparticles into polyamide fabrics significantly improved antimicrobial performance against both Gram-positive and Gram-negative bacteria. The antibacterial activity remained effective even after repeated washing cycles, indicating strong nanoparticle adhesion and long-term functionality.

The immersion-based impregnation method proved to be simple, scalable, environmentally friendly, and economically viable for industrial textile production. Furthermore, the antibacterial performance was maintained regardless of dyeing or softener treatment, increasing the potential applicability of these fabrics in healthcare, sportswear, hygiene products, and protective clothing.

Overall, ZnO nanoparticle-functionalized polyamide fabrics represent a promising strategy for reducing microbial proliferation, minimizing cross-contamination, and developing advanced antimicrobial textiles for modern biomedical and industrial applications.