Antibacterial and Antimycotic Activity of Cotton Fabrics, Impregnated with Silver and Binary Silver/Copper Nanoparticles

Effective method of obtaining of the bactericidal bandage materials by impregnation of cotton fabric by aqueous solutions of silver and copper salts followed by a certain regime of heat treatment is developed. The study of obtained materials by methods of optical spectroscopy, electron microscopy, and X-ray phase analysis showed the formation of crystalline silver nanoparticles (NPs) and bimetallic Ag/Cu composites with the corresponding surface plasmon resonance (SPR) bands in the absorption spectra. High antimicrobial and antimycotic properties of tissues with low concentrations of Ag and Ag/Cu nanoparticles (Ag/Cu NPs) (in the range 0.06–0.25 weight percent (wt%) for Ag and 0.015–0.13 wt% for Ag/Cu) is confirmed in experiments with a wide range of multidrug-resistant bacteria and fungi: Escherichia coli, Enterobacter aerogenes, Proteus mirabilis, Klebsiella pneumoniae, Candida albicans yeasts, and micromycetes. Textile materials with Ag NPs demonstrate high antibacterial activity, while fabrics doped with bimetallic composite Ag/Cu have pronounced antimycotic properties. Bactericidal and antifungal properties of the obtained materials do not change after a washing. Production of such materials is extremely fast, convenient, and cost-effective.

1 shows the concentration of the impregnation so-207 lutions near the symbol of each sample that will facilitate 208 the reproduction of the results. Usually, a piece of cotton 209 (10 g) was immersed in a 100 ml of solution of a certain 210 concentration of silver, copper, or Ag/Cu salts for 211 30 min. Amounts of adsorbed salts were determined 212 spectrophotometrically. Amounts of appearing Ag and 213 BMNP Ag/Cu were determined on calibration bands of 214 diffusion reflectance spectra (DRS) of dry fabrics after 215 the ironing procedure.  Table 1.

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The mechanism of reduction of metal ions to the NPs 245 on the surface of the cotton by gentle heat treatment f2:1 Fig. 2 Formation a bond between the metal ion and OH group f2:2 of cellulose f1:1 Fig. 1 Structural formula of a fragment of the cellulose 246 and their stability in relation to leaching of the metal 247 particles or ions upon contact with water and biological 248 fluids is not entirely clear. It is known that cotton is 249 99.6 % cellulose, and the rest is ash-like substance. 250 Cellulose is a long chain polymer molecule consisting of 251 repeating glucosidic residues, 300-10,000 glucose 252 residues, without side loops. Сellulose contains reducing 253 oligosaccharides. Their aldehyde function presumably 254 can promote the process of silver and copper ion reduc-255 tion (probably analogous to the reaction of "silver 256 mirror"). Figure   F1 1 shows a fragment of the polymeric 257 chain of cellulose.
f4:1 Fig. 4 Absorption spectra of fabrics with BMNP (1-3); spectra 4-Ag NPs, C of BMNP with Ag: Cu ratio are 1-8 × 10 −2 g/m 2 , 2-8 × 10 −3 g/m 2 , f4:2 3 -8×1 0 −4 g/m 2 ; spectra 4-Ag NPs, 4'-Cu NPs in colloid solutions are shown for comparison f3:1 Fig. 3 a Absorption spectra of tissues with Ag NPs corresponding to 1-8 × 10 −2 g/m 2 , 2-8 × 10 −3 g/m 2 , 3-8 × 10 −4 g/m 2 , and (4) -absorption f3:2 spectrum of the original fabric. b Absorption spectra of tissues containing copper with the same concentration of Cu, g/m 2 of tissue (4) -absorption f3:3 spectrum of the original fabric We can assume also the concentration of metal ions 259 around OH-groups and the bond formation between 260 the metal cations and hydroxyls of cellulose (Fig.   F2 2). The 261 water molecules are included in the coordination sphere 262 of metal ions, simultaneously forming a hydrogen bond 263 with OH-groups of cellulose. The Ag + ions have a rela-264 tively high reduction potential and are reduced to Ag 265 atoms at low temperature (160-200°C in air). The re-266 duction of copper ions requires a higher temperature; 267 however, when impregnated in the cotton, there is a 268 danger of destruction of tissue due to carbonization 269 process. Therefore, the ironing of tissues soaked in a salt 270 solution was carried out in all cases at temperatures of 271 200 to 220°C. The OH-groups of cellulose are oxidized 272 to carboxyl groups. The fabric retains its structure; here-273 with according to FTIR [17], stretching band at 1720 cm 274 −1 decreases due to the interaction between carboxyl 275 groups and metal ions.  It is possible to suppose that in a bimetallic 305 composites at heat treatment, Ag NPs precipitate on 306 the copper oxide particles as a shell. As a whole, it is 307 possible to suppose that under the impregnation and 308 heat treatment of cotton with salts of metals, a basis 309 of cotton, a cellulose, is simultaneously the reductant 310 of ions and stabilizer of appearing NPs. This question 311 needs further investigation.

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In [19], the spectrum of Ag/Cu BMNP in a thin 313 film of polyelectrolyte is attributed by the authors to 314 the alloy also only slightly differs in the position of 315 SPR of Ag NPs, though one would expect a much 316 larger wavelength shift in the case of formation of the 317 alloy. According to [19], in Ag/Cu alloy, silver and 318 copper are close to each other in electrical contact 319 and have a disordered random distribution of Ag and 320 Cu atoms inside an enclosed structure and therefore 321 do not possess crystallinity.  Thus, advantages of fabrics are the substitution of 352 noble metal silver on copper, simplicity of their pro-353 duction and storage, stability after washing, and main-354 tenance of bactericidal action for a long time.

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The results of determining the effect of tissue samples 356 with nanoparticles of silver and copper in clinical iso-357 lates of bacteria, fungi of the genus Candida, and micro-358 mycetes are shown in the diagram (Fig.   F7   7).

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Ratio Ag:Cu in BMNPs in gauzes is 1:1 (blue), with 360 the content of metal 1.3·10 −5 :1.3·10 −1 g/m 2 . Tissues 361 with a corresponding number of binary Ag/Cu have 362 pronounced bactericidal activity. As can be seen from 363 the above data, the fabrics impregnated with BMNPs 364 are the most effective in relation to most of the in-365 vestigated test cultures. The maximal area of growth 366 inhibition around the tissue for all studied bacteria, 367 fungi, and micromycetes are detected for bimetallic 368 composites. Cu ions and particles in the fabric do not 369 found expressed antibacterial action. Kinetics of 370 leaching of NPs with water from tissue samples were 371 studied for 24 h. Metal ions were not detected in the 372 solution, indicating the strong fixation of the particles f7:1 Fig. 7 The effect of tissue samples with nanoparticles of silver and copper in clinical isolates of bacteria, fungi of the genus Candida, f7:2 and micromycetes