Synthesis of silver nanoparticles and antibacterial property of silk fabrics treated by silver nanoparticles
© Zhang et al.; licensee Springer. 2014
Received: 3 December 2013
Accepted: 15 April 2014
Published: 7 May 2014
A silver nanoparticle solution was prepared in one step by mixing AgNO3 and a multi-amino compound (RSD-NH2) solution under ambient condition. RSD-NH2 was in-house synthesized by methacrylate and polyethylene polyamine in methanol, which has abundant amino and imino groups. However, the characterization of silver nanoparticles indicated that these nanoparticles are easy to agglomerate in solution. Therefore, an in situ synthesis method of silver nanoparticles on the silk fabrics was developed. The examined results confirmed that the in situ synthesized silver nanoparticles were evenly distributed on the surface of fibers. The inhibition zone test and the antibacterial rate demonstrated that the finished fabrics have an excellent antibacterial property against Staphylococcus aureus and Escherichia coli. Moreover, the nanosilver-treated silk fabrics were laundered 0, 5, 10, 20, and 50 times and still retained the exceptional antibacterial property. When the treated fabrics were washed 50 times, the antibacterial rate is more than 97.43% for S. aureus and 99.86% for E. coli. The excellent laundering durability may be attributed to the tight binding between silver nanoparticles and silk fibers through the in situ synthesis. This method provides an economic method to enhance the antibacterial capability of silk fabrics with good resistance to washings.
With the development of science and technology and the improvement of the living standard, people have continuously strengthened their awareness on health and environmental protection of clothing. Silk fabrics are highly popular with people for their excellent properties such as softness and gorgeous appearance, so they enjoy the honor as ‘The Queen of Fibers.’ However, silk fabrics provide an excellent environment for microorganisms to reproduce because of their large surface area and ability to retain moisture in the grids of fabrics. Therefore, to study and to improve the antibacterial properties of silk fabrics have an important influence on social significance and economic benefits[2–4].
To enhance the antibacterial properties of silk fabrics, silver nanoparticles are utilized to be attached onto the fabrics, although the mechanism is still in debate. In previous studies, it was indicated that the use of a strong reductant such as borohydride promotes the formation of silver nanoparticles in the solution, which have a narrow size distribution. However, the severe deficiency confronted during the preparation of nanoparticles is the stability of the solution and the aggregation of nanoparticles[6–9]. In order to solve this problem, various methods are developed by researchers, such as the addition of surfactants (polyvinyl pyrrolidone and polyethylene glycol), spray pyrolysis, low plasma, and so on[5, 10, 11]. Nevertheless, the synthesis of a monodisperse and stable silver nanoparticle suspension is challenging and may go through tedious and complex procedures, which may hinder the practical applications of silver nanoparticles on textiles.
In this paper, we developed a method to synthesize a multi-amino compound (RSD-NH2) using methacrylate and polyethylene polyamine as a precursor with the presence of methanol.
The mass of mulberry silk fabric is 60 g/m2 (purchased from Xinchang Co. Ltd, Guangzhou, China). Methacrylate, polyethylene polyamine, methanol, sodium sulfide (Na2S), silver nitrate (AgNO3), and nitric acid (HNO3) in analytical grade were purchased from Sinopharm Chemical Reagent Co. Ltd. (Beijing, China). The multi-amino compound (RSD-NH2) was prepared in the laboratory. Nutrient broth and nutrient agar, which are both biochemical reagents to culture bacteria, were purchased from Scas Ecoscience Technology Inc. (Shanghai, China). Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 8099) were obtained from the College of Life Science, Soochow University (China).
Synthesis of the multi-amino compound (RSD-NH2)
Polyethylene polyamine (1 M, 104 ml) was added in a 250-ml three-neck round-bottomed glass flask equipped with a constant-voltage dropping funnel, a thermometer, and a nitrogen inlet tube. The solution was stirred with a magnetic agitator. The flask was cooled to 24°C using a circulating water bath. Simultaneously, the mixture of methacrylate (1 M, 86 ml) in methanol was dropped slowly into the flask through the funnel. Afterwards, the reacting solution in the flask was removed from the water bath and left stirring for 4 h at room temperature. AB2-type monomers were synthesized, which made the solution present a light yellow color. The solution was transferred to an eggplant-shaped flask and put into an automatic rotary vacuum evaporator. After evaporation of methanol under low pressure, the temperature was raised to 150°C using an oil bath to initiate the polymerization of the monomers. Eventually, a yellowish viscous multi-amino compound (RSD-NH2) was obtained with a 4-h polymerization.
Preparation of the silver nanoparticles
Silver nitrate (AgNO3) and the multi-amino compound (RSD-NH2) were dissolved in deionized water, separately. Then AgNO3 aqueous solution was added dropwise into the RSD-NH2 solution under vigorous stirring. The initial concentrations of the reaction components were 0.017, 0.085, 0.17, and 0.255 g/l for AgNO3 and 2 g/l for RSD-NH2. The reacting mixture was kept stirring at room temperature until reduction of Ag+ to Ag was completed and brown silver nanoparticles appeared.
Characterization of the silver nanoparticles
The size distribution and polydispersity of the silver nanoparticles were determined by dynamic light scattering (DLS) using a HPPS 5001 grain size analyzer (Malvern Instruments Ltd., Malvern, UK). Transmission electron microscopy (TEM) micrographs were obtained using a Tecnai G220 TEM (FEI Company, Hillsboro, OR, USA) operated at a 300-kV accelerating voltage. TEM samples were prepared by evaporating a drop of nanoparticle solution onto a 200-mesh copper grid, which was coated with a carbon support film. UV-visible (UV-vis) absorption spectra were recorded using an UV-3010 spectrophotometer (Shimadzu Ltd, Japan). K/S absorption spectra of treated silk fabrics were tested under a D65 illuminant at 10° observer using an Ultrascan XE spectrophotometer (HunterLab Co. Ltd., Reston, VA, USA). The X-ray diffraction (XRD) patterns of the silver nanoparticles were taken in the 2θ range of 20° to 80° at a scanning rate of 2°/min using Cu Kα radiation with a model D/max3c X-ray detector diffraction system (Rigaku Ltd, Japan).
For Fourier transform infrared (FTIR) analysis, the colloidal silver solution was poured into acetone and the resulting precipitates were dried for characterization. FTIR spectra were performed on a Nicolet 5700 FTIR spectrophotometer (Thermo Electron Corporation, USA).
Preparation of silver nanoparticle-treated silk fabrics
The silk fabrics were immersed into the solution of mixed AgNO3 and RSD-NH2 at their respective concentration with the process of dipping and rolling twice. Subsequently, the fabrics were steamed for 30 min in a steam engine (BTZS10A, China). After that, the fabrics were washed by deionized water and dried at ambient temperature to produce the finished silk fabric.
Antibacterial effect of nanoparticle-treated silk fabrics
The morphology and distribution of silver nanoparticles on the surface of fabrics were observed using a scanning electron microscope (SEM; S-570, Japan). The antibacterial effect of silver nanoparticle-treated silk fabrics was tested against E. coli and S. aureus by using a shaking flask method according to the antibacterial standard of knitted products (FZ/T 73023-2006, China). This standard specified the requirements of the antibacterial fabric, test methods, and inspection rules, which are applicable to the antibacterial fabrics made by natural fiber, chemical fiber, and blended fiber.
where A and B are the bacterial colonies of the original silk fabrics and the silver-treated silk fabrics, respectively.
To evaluate the durability of the nanoparticle-treated silk fabrics against repeated launderings, AATCC Test Method 61-1996 was applied. An AATCC standard wash machine (Atlas Launder-Ometer) and detergent (AATCC Standard Detergent WOB) were used. Samples were cut into several 5 × 15 cm2 swatches and put into a stainless steel container with 150 ml of 0.15% (w/v) WOB detergent solution and 50 steel balls (0.25 in. in diameter) at 49°C for various washing times to simulate 5, 10, 20, and 50 wash cycles of home/commercial launderings.
Results and discussion
Synthesis of silver nanoparticles in solution
Size of the micro-crystal of the resulting nanosilver particles
Size of the micro-crystal (nm)
Characterization and antibacterial ability of in situ synthesized silver nanoparticles on silk fabrics
After the in situ reaction on the surface of silk fabrics was completed, the dried fabrics visually showed a bright yellow color. Generally, nanosilver particles are considered as a good antimicrobial agent on silk fabrics. To study the antimicrobial activities of silver nanoparticle-treated silk fabrics, E. coli and S. aureus were selected to perform antibacterial experiments.
The WI, silver content, and antibacterial rate of nanosilver-treated fabrics
Silver content (mg/kg fabric)
Surviving cells (CFU/ml)
Surviving cells (CFU/ml)
2.28 × 106
4.37 × 106
1.53 × 102
2.22 × 103
4.56 × 102
2.09 × 103
3.19 × 103
1.39 × 103
4.52 × 102
9.1 × 102
1.62 × 102
8.7 × 102
The WI, silver content, and antibacterial rate of different washing times
Silver content (mg/kg)
Surviving cells (CFU/ml)
Surviving cells (CFU/ml)
2.28 × 106
4.37 × 106
1.16 × 103
8.74 × 102
3.44 × 103
1.74 × 103
1.28 × 103
6.11 × 103
2.53 × 103
1.48 × 103
5.86 × 103
6.11 × 103
The excellent laundering durability of the silver nanoparticle-treated silk fabrics may be caused by the following reasons. Firstly, some imino groups of RSD-NH2 form a silver ammonia complex with silver nanoparticles, which easily penetrate into the amorphous zone of silk fibers. Secondly, silk is a protein fiber and amino acid is its basic structural unit, which has a large number of amino and carboxyl groups on the surface. The van der Waals force between molecules, as well as the hydrogen bond, will enhance the bonding between silver particles and silk fabrics.
A silver nanoparticle solution was prepared in one step by mixing AgNO3 and RSD-NH2 solution under vigorous stirring at room temperature. The multi-amino compound (RSD-NH2), which has abundant amino and imino groups, was synthesized by methacrylate and polyethylene polyamine in methanol. The formation of silver nanoparticles was characterized by various methods. However, the results indicated that silver nanoparticles easily agglomerate in ambient condition. Therefore, an in situ synthesis method was conducted through the reaction between the multi-amino compound (RSD-NH2) and the silver nitrate solution. The surface morphology, whiteness, silver content, antibacterial activity, and washing durability of nanosilver-treated fabrics were examined. The experimental results confirmed that the in situ synthesized silver nanoparticles evenly distributed on the surface of fibers. The inhibition zone and the antibacterial rate demonstrated that the finished fabrics have an excellent antibacterial property against S. aureus and E. coli. When the nanosilver-treated fabric which included a silver content of 98.65 mg/kg was washed 50 times, the silver content slightly decreased from 98.65 to 81.65 mg/kg and the corresponding whiteness increased. However, it is surprising that the antibacterial rate is still more than 97.43% for S. aureus and 99.86% for E. coli after 50 washings.
This research was supported by the National High Technology Research and Development Program of China (No. 2012AA030313).
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