22nd International Symposium on Plasma Chemistry July 5-10, 2015; Antwerp, Belgium

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Nanoparticle incorporated non-woven fabric prepared by atmospheric pressure plasma process for antibacterial property

X. Deng1, A. Nikiforov1, D. Vujosevic2, V. Vuksanovic2 and C. Leys1

1 Ghent University, Department of Applied Physics, Sint-Pietersnieuwstraat 41, BE-9000, Ghent, Belgium

2 Institute of Public Health, Center for Medical Microbiology, DzonaDzeksona bb, Podgorica, 81000, Montenegro

Abstract: A simple method for the preparation of nanoparticle incorporated non-woven fabric with effective antibacterial property has been investigated based on atmospheric pressure plasma process. In the work, three different nanoparticles (silver, copper and zinc oxide nanoparticles) were employed as antibiotics. The surface chemistry and antibacterial activity of the samples were investigated.

Keywords: nanocomposite film, antibacterial, plasma process, atmospheric pressure, XPS

1. Introduction

Non-woven materials have been used widely in applications ranging from medical dressing to everyday cleaning products. In recent years, a lot of attention has been paid to achieve multifunctional performance of the fabrics, especially in packing, health and hygiene field [1]. Due to the potential for growth of pathogenic microorganisms which can produce and spread diseases, non-woven fabrics with antibacterial property are very interesting and have been extensively studied. Usual procedure for obtaining antibacterial textile material is textile finishing with antibacterial agents. The molecular antibacterials traditionally used to against bacterial face several disadvantages, including the worldwide emergency of antibiotic resistance, difficult to be incorporated into many materials and sensitive to harsh environments during many industrial processes. Inorganic compounds in nanosize present strong antibacterial activity at low concentration due to their high surface area to volume ratio and unique chemical and physical properties. Currently, the metallic nanoparticles, like silver (Ag-NP), copper (Cu-NP) and zinc oxide (ZnO-NP), are thoroughly being explored and extensively investigated as potential antibiotics, because of their pronounced biocidal activity and much more stability under extreme conditions [2].

Recently, we proposed a novel method for the preparation of polyethylene terephthalate (PET) non-woven fabrics with antibacterial properties made with firmly immobilizing silver nanoparticles via double layer of plasma deposited organic films. The method is based on firmly immobilizing nanoparticles via double layer of plasma deposited organic films. It has been confirmed that a barrier layer can prevent the release of Ag-NPs and control the release of silver ions.

The presented work investigates a simple way to realize the incorporation of three different types of nanoparticles (Ag-NP, Cu-NP, ZnO-NP). The surface chemistry of the materials was analyzed by XPS. The antibacterial activity of the samples was tested against Staphylococcus aureus

(S. aureus) and Escherichia coli (E. coli) as the representatives of Gram-negative bacteria and Gram-positive bacteria, respectively. 2. Experimental

Nanoparticle embedded non-woven PET fabrics were prepared through a three step procedure. At first, an organosilicon thin film was deposited on the surface of the PET fabrics using a plasma jet deposition system [3]. This 70 nm layer is used as a reservation layer for the silver immobilization and control of the silver nanoparticles adhesion to the PET fabrics. The plasma head is mounted on a robotic arm in order to achieve a large scale uniform treatment.

Then, the samples with plasma deposited layer were immersed into a suspension of nanoparticles in ethanol and raised for drying. Silver nanoparticles (SSNANO, USA) of 20 nm size with a purity of 99.95%, copper nanoparticles (Sigma-Aldrich, Belgium) of 50 nm size with a purity of 99.9%, and zinc oxide nanoparticles (Sigma-Aldrich, Belgium) of 50 nm size with a purity of 99.7% were used throughout the experiments as purchased. In the final step, a second layer (also called barrier layer) of organosilicon film with a thickness of 10 nm was deposited. 3. Results and discussion

The surface element composition and chemical state of the treated fabrics were studied by XPS and the results are presented in Fig. 1. The value of 285 eV of the hydrocarbon C1s core level is used as a calibration of the energy scale.

The XPS survey spectra acquired from the control sample and the nanoparticle incorporated samples were presented in Fig. 1a. For the control sample which is corresponding to the fabric treated with organosilicon film only, it was composited of Si, O, and C. The appearance of Ag, Cu and Zn peaks in XPS spectra for the samples after nanoparticle incorporation reveals that the corresponding nanoparticles have been successfully

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decorated into the materials. Figs. 1b-d display the XPS high resolution spectra of silver, copper and zinc for those samples with corresponding nanoparticles. In Fig. 1b, peaks at 368.2 eV and 374.2 eV are assigned to Ag 3d5/2 and Ag 3d3/2, respectively. These peaks have a splitting of 3d doublet with 6 eV indicating the presence of metallic silver. While, comparing to the binding energy of Ag 3d5/2 for bulk metal Ag at 368.2 eV, a positive chemical shift observed for Ag 3d5/2 (at 368.1 eV) suggests that silver nanoparticles are partly oxidized in the process [3]. The Cu 2p1/2 and Cu 2p3/2 (Figure 1(c)) centred at 952.2 eV and 932.4 eV with a spin-orbit separation of 18.8 eV for the sample embedding Cu-NPs. The absent of shake-up peaks at about 941.5 eV indicates no Cu2+ are presented in the sample [4]. However, it is difficult to identify Cu0 and Cu+ due to the limitation of XPS resolution, as mentioned by Chen [5]. Fig. 1d represents the XPS spectra of Zn 2p, and the peak position of Zn 2p1/2 and Zn 2p3/2 locate at 1045.2 eV and 1022.2 eV respectively.

Figure 1. XPS results of the nanocomposite films: (a) survey XPS spectra; (b) Ag3d XPS spectrum; (c) Cu2p spectrum; (d) Zn2p spectrum.

In the antibacterial test, the non-woven fabrics coved with organosilicon films were used as a control sample. The test solution of 0.5 McF (~ 1.5 x 108 CFU/ml) for each bacterium is diluted with sterile phosphate buffered saline (PBS) to a concentration of about 106. Afterwards, the samples were seeded with fresh E. coli and S. aureus culture, and then were incubated at 37 ºC for 24 h. After well vortexed, a quantity of 100 µl of homogenized solution after incubation was spread onto three Mueller-Hinton (MH) agars, which were incubated 24 h at 37 ºC for colony forming counts. Percent reduction of organisms R which indicates biostatic efficiency resulting from contact with the specimen was determined using R (%) = (B-A)/B, where A is CFU per millilitre for the medium with the treated substrate after incubation, and B is CFU per millilitre of the medium with the control samples after incubation.

The calculated antibacterial rate against E. coli and S. aureus are shown in Fig. 2. As one can see from the figure, the samples incorporated the three nanoparticles exhibits effective antibacterial activity against those two microorganisms. Since the concentrations and the size of incorporated nanoparticles are different, comparison on the antibacterial efficiency among the three types of nanoparticles will not be discussed in the contribution.

Figure 2. Efficiency of the samples with three types of nanoparticles against E. coli and S. aureus. Each data point and error bar represents the mean and standard errors, respectively, of independent triplicates.

Our recent work proofs that the double layer structure can firmly immobilize the incorporated nanoparticles during mechanical washing cycles, which suggests the release of the nanoparticles can be avoid in the test. Thus, the direct interaction between nanoparticles and bacterial membranes is negligible in the work. Then, the main antibacterial mechanism could be expected by the generation of active oxygen species, especially for ZnO,[6] and the release of the bacteriostatic Ag+ and Cu2+ ions for the non-woven fabrics incorporated with Ag-NP and Cu-NP respectively [7, 8]. 4. Conclusions

Non-woven fabrics incorporated with three types of nanoparticles, Ag-NP, Cu-NP and ZnO-NP, have been prepared by a three step method based on atmospheric pressure plasma process. The XPS results reveal the nanoparticles have been successfully embedded into the fabrics. All nanofabrics show effective antibacterial activity against E. coli (a) and S. aureus. 5. Acknowledgements

The work was supported by STSM Grant of the COST Action MP1101. 6. References [1] S. Ramakrishna, et al. Composites Sci. Technol., 61,

9 (2001) [2] A. Méndez-Vilas. Science against microbial

pathogen: communicating current research and technological advances. Formatex Research Centre (Badajoz, Spain) (2011)

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[3] X. Deng, et al. Plasma Process. Polymers, 11, 11 (2014)

[4] Y.H. Kim, et al. J. Phys. Chem. B, 110, 49 (2006) [5] Z. Chen, et al. Nanotechnology, 24, 26 (2013) [6] O. Yamamoto. Int. J. Inorg. Mater., 3, 7 (2001) [7] N. Cioffi, et al. Anal. Bioanal. Chem., 381, 3 (2005) [8] Y.-J. Lee, et al. Environm. Toxicology Chem., 31, 1

(2012)