1173 ISSN 1229-9197 (print version) ISSN 1875-0052 (electronic version) Fibers and Polymers 2020, Vol.21, No.6, 1173-1179 Effects of Hydrodynamic Diameter of Nanoparticles on Antibacterial Activity and Durability of Ag-treated Cotton Fabrics Mohammad Ehsan Momeni Heravi * Department of Fashion Design, Mashhad Branch, Islamic Azad University, Mashhad 9187147578, Iran (Received July 17, 2019; Revised October 8, 2019; Accepted October 17, 2019) Abstract: In this paper, silver nanoparticles (Ag-NPs) colloidal suspensions with different particle sizes of 5 to 40 nm were prepared. Dynamic light scattering (DLS) technique showed that the average hydrodynamic diameters of Ag-NPs were much larger than the particle diameters obtained using transmission electron microscopy and UV-Vis spectroscopy. The as-prepared Ag-NPs with different average hydrodynamic diameters were incorporated in cotton fabrics by the pad-dry-cure method. The silver content before and after washing cycles were determined by inductively coupled plasma spectrometry (ICP). The antibacterial properties of the fabrics after 0, 5 and 10 laundering cycles against both the Gram-negative bacterium of Escherichia coli (E. coli) and the Gram-positive bacterium of Staphylococcus aureus (S. aureus) were examined and a clear volcano trend was observed between the bacterial reduction rate (BR) and the hydrodynamic diameter of Ag-NPs loaded on the fibers. The cotton fabric treated by the Ag-NPs with the hydrodynamic diameter of 52 nm, exhibited the highest antibacterial activity (about 98 %) after 10 laundering cycles, while the other samples on either side of the volcano were less active. The cytotoxicity of the cotton fabrics treated with Ag-NPs was assayed on mouse embryonic fibroblast cells and evaluated by an MTT assay. The results showed that Ag-NPs were not toxic. Field emission scanning electron microscopy (FESEM) obtained from the cotton fabric before and after washing cycles demonstrated that the Ag-NPs had tight bonds with the surface of cotton fabric. Keywords: Antibacterial properties, Silver, Nanoparticle, Cotton, Hydrodynamic diameter Introduction Nowadays, the nanoscience as a new field is not only used in modern technologies, but applied to improve the materials properties in food, textile, building, etc industries which are known as traditional industries. Among different kinds of nanostructures, around 30 % of the products using nano- technology contain silver nanoparticles as highly effective antibacterial agents [1,2]. In medicine, Ag nanoparticles (Ag-NPs) can be used as coating materials for medical devices, such as catheters or bandages [3]. In addition, silver nanostructures are widely used in the textile industry owing to the wrinkle resistance and antibacterial properties [4-7]. In this industry, cotton is the most widely used natural fiber for textiles, because of its ability to control moisture, insulate, hypoallergenic, weatherproof and ease for mass production with low price. However, microorganisms can easily propagate through the cotton fabrics and grow on the fibers, due to their ability to store humidity and having a high specific surface area. As highly effective antibacterial agents, Ag-NPs greatly impact on broad range of microorganisms, in addition to showing a low toxicity toward mammalian cells [8]. Moreover, good adhesion between nanoparticles and textile fibers is important, in order to maintain the antibacterial activity of the fabric. In this case, reasonable binding agents as a link between the fibers and the nanoparticles play a crucial role to minimize the nanoparticles release over time and washing cycles. In many researches, improving durability by creating chemical bonds or active sites has been put forward. Carboxymethyl chitosan [9], Carboxyl groups accompanying with plasma pretreatment of fibers [10], polycarboxylic acids such as 1,2,3,4-butanetetracarboxylic acid (BTCA) [11], citric acid [12] and self-cross-linking acrylic binders [13-15] has been suggested to replace the conventional materials. Acrylic binders as a cost effective agent can provide strong cross-linking between the antibacterial agent and cotton fabrics. Here, we show that besides reasonable binding agent, the hydrodynamic diameter of particles is important to make a robust link to fibers. In this study, colloidal Ag-NPs with different sizes from 5 to 40 nm were prepared. The structure, morphology, hydrodynamic diameter and particle size distribution were studied by ultraviolet-visible spectroscopy (UV-Vis spectroscopy), X-ray diffraction (XRD), dynamic light scattering (DLS) technique and transmission electron microscopy (TEM). The cotton fabrics were incorporated with 50 ppm of the Ag-NPs suspensions by the pad-dry-cure method. The antibacterial properties of fabrics washed for 0, 5 and 10 times against both the Gram-positive bacterium of Staphylococcus aureus (S. aureus) and the Gram-negative bacterium of Escherichia coli (E. coli) were investigated. The silver content on the fibers before and after washing cycles were estimated by ICP spectrometry. The dependence of antibacterial activity on hydrodynamic diameters of Ag- *Corresponding author: momeni5892@mshdiau.ac.ir DOI 10.1007/s12221-020-9748-4 Communication