Antimicrobial properties of silver nanoparticles synthesized by bioaffinity adsorption coupled with TiO2 photocatalysis

BACKGROUND: On the basis of effective bioaffinity adsorption of Ag⁺, silver nanoparticles (Ag NPs) were synthesized on the surface of chitosan‐TiO₂ adsorbent (CTA) by TiO₂ photocatalysis for crystal growth. RESULTS: Among the microstructure characterizations of the resulting silver nanoparticles‐ loaded chitosan‐TiO₂ adsorbent (Ag‐CTA), X‐ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive X‐ray (EDX) revealed the formation of metallic Ag on the CTA, which was further confirmed by the surface plasmon resonance of Ag NPs in the UV‐visible absorption spectrum. The underlying mechanism behind the formation of Ag NPs on the CTA by TiO₂ photoreduction was studied by Fourier transform infrared (FTIR) spectroscopy. The distinctive feature of Ag‐CTA after adsorption was the highly efficient antimicrobial activity in inactivating different test strains. In the case of Escherichia coli, 1.50 mg 1.67 wt% Ag‐CTA could totally inhibit 1.0–1.2 × 10⁷ colony forming units (CFU) in 100 mL nutrient medium, which was superior to that previously reported. CONCLUSIONS: CTA effectively adsorbed the precious metal ion Ag⁺ onto active imprinting sites on the adsorbent and then exerted efficient antimicrobial effects against diverse microbes. This research will be useful for designing a novel CTA‐based wastewater treatment for multi‐functional performance. Copyright © 2010 Society of Chemical Industry     

Synthesis and antimicrobial activity of biocidal polymer–montmorillonite nanocomposites

The bioactive agents p‐hydroxymethylbenzoate, 2,4‐dihydroxymethylbenzoate and methylsalicylate were reacted with polyoxyalkylene (D_230–2000)–montmorillonite (MMT) intercalated nanocomposites. D_230–2000–MMT were prepared by an ion exchange process of Na‐MMT and? NH₃⁺ groups in polyoxyalkylene amine hydrochloride of three different molecular masses (D₂₃₀, D₄₀₀ and D₂₀₀₀). The results of X‐ray analysis and transmission electron microscopy show that D₂₀₀₀–MMT/p‐hydroxymethylbenzoate is an exfoliated nanocomposite, whereas in D₂₃₀–MMT/p‐hydroxymethylbenzoate, D₂₃₀–MMT/2,4‐dihydroxymethylbenzoate, D₂₃₀–MMT/methylsalicylate and D₄₀₀–MMT/p‐hydroxymethylbenzoate, having lower molecular mass and polymer loading, the MMT rearranges in an intercalated and flocculated structure. The amount of intercalated polymer and interaction between polymer and layered silicate were determined using thermogravimetric analysis and Infrared spectroscopy. The antimicrobial activities of the nanocomposites were qualitatively and quantitatively assessed by agar diffusion tests and minimal inhibitory concentration values against a Gram‐negative bacterium (Escherichia coli NCIM 2065), a Gram‐positive bacterium (Bacillus subtilis ATCC) and fungi (Candida albicans SC5314 and Cryptococcus neoformans). The D₂₀₀₀–MMT/p‐hydroxymethylbenzoate nanocomposite strongly inhibits the growth of all the micro‐organisms tested. The diameter of the inhibition zone varies according to the type of micro‐organism tested. The effect of nanocomposite concentration on morphology, respiration and release of calcium, potassium and sodium ions of the test micro‐organisms was examined. Copyright © 2011 Society of Chemical Industry     

Antibacterial activity of resin-containing triethylenetetramine side chains and/or thiol groups–metal complexes

Four chelating resins containing triethylenetetramine side chains and/or thiol groups were made from macroreticular 2,3-epithiopropyl methacrylate, styrene–divinylbenzene (DVB), or methyl methacrylate–DVB copolymer beads, and then the resins bearing metal ions such as Ag⁺, Cu²⁺, and Zn²⁺ were made. The antibacterial activity of the resins bearing metal ions against Escherichia coli (E. coli) or Staphylococcus aureus (S. aureus) was investigated. The resins containing thiol groups showed the higher adsorption capacity for silver ions than for other metal ions. The resins, which contain both triethylenetetramine side chains and thiol groups, bearing silver ions (RE-TTA-Ag) exhibited high antibacterial activity against bacteria, especially E. coli, without the residual silver ions in water after contacting with bacteria. The activity of the RE-TTA-Ag did not decrease even after reusing several time. © 1996 John Wiley & Sons, Inc.     

Efficiency of silver‐based antibacterial additives and its influence in thermoplastic elastomers

Styrene‐butylene/ethylene‐styrene‐based thermoplastic elastomers (TPE) are polymers with soft touch properties that are widely used for manufacturing devices that involve hand contact. However, when contaminated with microorganisms these products can contribute to spreading diseases. The incorporation of antibacterial additives can help maintain low bacteria counts. This work evaluated the antibacterial action of TPE loaded with silver ions and silver nanoparticles. The additives nanosilver on fumed silica (NpAg_silica), silver phosphate glass (Ag⁺_phosphate), and bentonite organomodified with silver (Ag⁺_bentonite) were added to the TPE formulation. The compounds were evaluated for tensile and thermal properties and antimicrobial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). All the additives eliminated over 90% of E. coli, but only NpAg_silica killed more than 80% of S. aureus population. The better effect of NpAg_silica was attributed to the additive's high specific surface area, which promoted greater contact with bacteria cells. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43956.     

Ionic liquid intercalated clay nanofillers for chromatographic applications

In this study, the preparation and characterization of ionic liquid (IL) intercalated montmorillonite (MMT) and their application as a micro-solid phase extraction material for the determination of Chlorpyrifos (CP) pesticide in water samples were reported. The ionic liquids bearing different chain lengths [1-methyl-3-octylimidazolium bromide (C₈mimBr), 1-methyl-3-undecyl-imidazolium bromide (C₁₂mimBr) and 1-methyl-3-octadecyl-imidazolium bromide (C₁₈mimBr)] were intercalated in the galleries of MMT. The IL-intercalated MMTs were characterized by means of XRD and TG methods. The (C₁₂mimBr)-intercalated MMT had the highest sorption efficiency for the CP, which was 32 times higher than the original MMT. We also optimized the parameters for extracting CP from the (C₁₂mimBr)-intercalated MMT.     

Preparation and characterization of antibacterial chitosan/Ag–montmorillonite with improved dynamic mechanic properties

Chitosan/Ag–montmorillonite (CS/Ag–MMT) nanocomposite was obtained via solution intercalation. The X‐ray diffraction and transmission electron microscopy results indicated the successful formation of intercalated‐and‐exfoliated nanostructures at low Ag–MMT contents and intercalated‐and‐flocculated nanostructures at high Ag–MMT contents. The CS/Ag–MMT nanocomposite with 7 wt% Ag–MMT presented a very high inhibition ratio against Staphylococcus aureus (>70%), and its bacterial inhibition zone diameter was 3.2 mm larger than that of CS, which showed remarkable antibacterial activity. When the Ag–MMT content was 5 wt%, the E′ of CS/Ag–MMT was increased to 3,261 MPa, which was 195% higher than CS and exhibited excellent mechanic property. The DMA test results showed the T_g of CS/Ag–MMT shifted to a higher temperature, suggesting the Ag–MMT interlayer not only interacted quite strongly with the reactive groups of CS but also restricted the motion of CS macromolecules, which was also verified by Fourier transform infrared spectrum measurements. POLYM. COMPOS., 35:1980–1988, 2014. © 2014 Society of Plastics Engineers     

Study on ibuprofen/montmorillonite intercalation composites as drug release system

The present paper focused on the intercalation of ibuprofen (IBU) into montmorillonite as a sustained release drug carrier. The intercalation compounds were characterized by X-ray diffraction (XRD), Fourier transformed infrared (FT-IR), and thermogravimetric analysis (TGA). The basal spacing of montmorillonite increased from 1.25 nm to 1.57 nm. The decomposition temperature of intercalated IBU was increased to 471 °C. The in vitro release experiments revealed that IBU was released from MMT steadily and pH dependent.     

Preparation and characterization of acrylic acid/itaconic acid hydrogel coatings containing silver nanoparticles

Hydrogel silver nanocomposites have been used in applications with excellent antibacterial performance. Acrylic acid (AA)/itaconic acid (IA) hydrogels silver nanocomposites were prepared and applied as a coating on a textile substrate. Hydrogel matrices were synthesized first by the polymerization of an AA/IA aqueous (80/20 v/v) solution and mixed with 2‐2‐azobis(2‐methylpropionamide) diclorohydrate and N,N′‐methylene bisacrylamide until the hydrogel was formed. Silver nanoparticles were generated throughout the hydrogel networks with an in situ method via the incorporation of the silver ions and subsequent reduction with sodium borohydride. Cotton (C) and cotton/polyester (CP) textile fibers were then coated with these hydrogel silver nanocomposites. The influence of these nanocomposite hydrogels on the properties of the textile fiber were investigated by infrared spectroscopy (attenuated total reflectance), scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and antibacterial tests against Pseudomona aeruginosa and Staphylococcus aureus. The better conditions, in which no serious aggregation of the silver nanoparticles occurred, were determined. It was proven that the textiles coated with hydrogels containing nanosilver had an excellent antibacterial abilities. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2713–2721, 2013     

Improving heat ageing and thermal properties of silicone rubber using montmorillonite clay

Heat ageing and thermal stability of a silicone rubber (SR) filled with montmorillonite clay (MMT) was investigated. Three types of rubber nanocomposites were prepared with highly exfoliated Cloisite 30B (SR/C30B), intercalated/exfoliated Cloisite Na⁺ (SR/Na⁺MMT), and highly intercalated Cloisite 20A (SR/C20A). This study showed that the SR/C30B nanocomposite exhibited excellent heat resistance in comparison to the other two nanocomposites and neat SR as revealed by higher retention strength. The thermal stability of the rubber in air was strongly dependent on the clay morphology and increased in the following order: highly intercalated/exfoliated SR/Na⁺MMT < highly intercalated SR/C20A < highly exfoliated SR/C30B. The thermogravimetric analyses of the SR/C30B nanocomposite showed a substantial increase in the final residue in comparison with the neat SR. This indicated a major improvement in the thermal stability of the rubber containing the exfoliated clay, which was also supported by the higher activation energy of decomposition measured for the nanocomposite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41061.     

Facile synthesis,antibacterial mechanisms and cytocompatibility of Ag–MnFe2O4 magnetic nanoparticles

Magnetic MnFe₂O₄ nanoparticles containing 0, 1 and 3 at.% silver, respectively were synthesized by one-pot sol-gel method for antibacterial applications in biomedical fields. Material characterizations indicate that MnFe₂O₄ begins crystallization at 134 °C and oxidation at 450 °C, the grain size and agglomeration degree increase with the silver content and silver exists as metallic state for the particles. The saturation magnetization decreases with the sintering temperature and slightly increases with the silver content, with the maximum of 50.0 emu/g obtained. Antibacterial tests by plate counting and PI-Hoechst 33342 staining suggest that the antibacterial activity of Ag–MnFe₂O₄ nanoparticles is silver content-dependent. Silver ions concentration measurement, β-galactosidase activity assay and transmission electron microscopic observation show that the antibacterial activity is dominated by the actions of the released silver ions, rather than the membrane cell impairment or reactive oxygen species-induced oxidative stress mechanism. MC3T3-E1 cell test demonstrates the best cytocompatibility of the nanoparticles with 3 at.% silver, which is likely related to the reduced cell endocytosis of the aggregated particles. The combination of magnetism, antibacterial activity and biocompatibility would make Ag–MnFe₂O₄ nanoparticles a potential multi-functional material in various biomedical applications.     

Novel antibacterial composite of coal/LLDPE loaded with silver ions

A novel antibacterial composite of coal/LLDPE (linear low density polyethylene) loaded with silver ions (ACCPE) was prepared by means of solid–liquid phase adsorption and extrusion. The composite was characterized by IR, XRD and SEM, and the mechanical, rheological, and Ag⁺‐releasing, and antibacterial properties of the composite were investigated. We discover that the ACCPE shows favorable mechanical properties, features a higher processability and antibacterial activity, and the coal and silver ion possess superimposed effect on antibacterial activity against Escherichia coli. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Tuned interactions of silver nanoparticles with ZSM-5 zeolite by adhesion-promoting poly(acrylic acid) deposited by electrospray ionization (ESI)

The electrospray ionization (ESI) method was used for deposition of thin films of poly(acrylic acid) (PAA) on Cu/ZSM-5 (5 wt.% Cu) and Ag–Cu/ZSM-5 (1 wt.% Ag and 4 wt.% Cu) composites. For comparative purposes, the ZSM-5 zeolite was synthesized under hydrothermal conditions and loaded with PAA under the same treating conditions as the composites. This method allowed the formation of uniform polymer films of controlled thickness on conductive substrates. The structural characteristics were characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, atomic force microscopy and X-ray diffraction (XRD). The deposited PAA layer over ZSM-5 acts as a common dispersing and stabilizing agent through coordination-driven guest-templated polymer via interaction of Ag⁺ and Cu²⁺ with carboxylic acid groups, thus increasing and controlling the adhesion and the release of metallic species. A short exposure to light and temperature has reduced the metal ions to Cu⁰ and Ag⁰ metallic nanoparticles. The results of XRD analysis let suggest that the interaction of Cu and Ag with carboxylic groups of PAA inhibits the formation of large metallic silver particles. These samples were being studied for their potential as antibacterial agents toward the bacterial strains such as Staphylococcus pneumonia, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa as Gram positive and Gram negative bacteria, respectively. Aspergillus fumigatus and Candida albicans as Fungi were also evaluated. The Cu/ZSM-5 and Ag–Cu/ZSM-5 nanocomposites coated with a 10 nm thick PAA layer exhibit significant antibacterial activity.     

Superabsorbent polymeric materials. XII. Effect of montmorillonite on water absorbency for poly(sodium acrylate) and montmorillonite nanocomposite superabsorbents

A series of novel xerogels based on sodium acrylate (NaA), montmorillonite (MMT), and N,N′‐methylene‐bisacrylamide (NMBA) were prepared by inverse suspension polymerization and water solution polymerization. The influences of pure MMT, intercalated MMT, the method of polymerization, and the content of the MMT in the copolymeric gels on the water absorbency and the initial absorption rate in deionized water and various salt solutions were investigated. Results showed that the water absorbency was increased by adding a small amount of the pure MMT into the copolymeric gels, but decreased by adding intercalated MMT into the gels. In addition, the water absorbency of the gels prepared by water solution polymerization was lower than that prepared by inverse suspension polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3422–3429, 2004     

Morphology,physical properties,silver release,and antimicrobial capacity of ionic silver‐loaded poly(l‐lactide) films of interest in food‐coating applications

In the present study, silver ions were incorporated into a poly‐(l ‐lactide) (PLA) matrix by a solvent casting technique using different solvents and glycerol as plasticizer. The effect of the different formulations on the morphology, thermal, mechanical and color properties were first evaluated. Additionally, a thorough study of the silver ions release to an aqueous environment was also monitored over time by anodic stripping voltammetry and correlated with the antimicrobial performance against S. enterica. The incorporation of silver contents of up to 1 wt % did not affect morphology, thermal or mechanical properties of the films. A sustainable, antibacterial effectiveness was found for the films in liquid medium and a breakpoint of 10–20 μg L^?1 silver was established under the stated conditions, evincing silver ion releasing technologies may be applied to liquid environments while complying with current legislation. This study provides insight into the structure properties relationship of these antibacterial polylactide materials of significant potential in coating applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41001.     

Silver‐loaded lyocell fibers modified by tempo‐mediated oxidation

The purpose of this research was to accomplish antimicrobial properties in lyocell fibers by Ag⁺ ions sorption from aqueous silver nitrate solution. Sorption properties of lyocell fibers were improved by the selective TEMPO‐mediated oxidation, i.e. oxidation with sodium hypochlorite and catalytic amount of sodium bromide and 2,2,6,6‐tetramethylpiperidine‐1‐oxy radical (TEMPO). The most suitable experimental conditions for the selective TEMPO‐mediated oxidation were determined by changing oxidation conditions: concentration of sodium hypochlorite, as well as duration of sorption. The obtained results showed that the maximum sorption capacity (0.809 mmol of Ag⁺ ions per gram of fibers) of modified lyocell fibers was obtained for the sample modified with 4.84 mmol NaClO per gram of cellulose, during 1 h. The antifungal activity of the TEMPO‐oxidized lyocell fibers with silver ions against fungi from the Candida family, Candida albicans (ATCC 24433), and antibacterial activity against two strains: Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) were confirmed in vitro. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of the structure of the onium iodide salts on the properties of modified montmorillonite

Dialkyl imidazoline, alkyl pyridine and alkyl quinoline containing salts have been synthesized and used as new surfactants for cationic exchange of layered silicates, such as montmorillonite (MMT) in order to evaluate their role in the formation of intercalated MMT clays. The new salts have been characterized by FTIR, ¹H, ¹³C‐NMR spectra. These compounds have been intercalated into the layers of MMT via a solution dispersion technique and the extent of the interlayer space expansion was confirmed by using wide angle X‐ray diffraction and FTIR spectra. Thermogravimetry analysis shows that these salts can be used in place of ammonium salts to produce organophilic clays with higher thermal stability than commercial alkyl ammonium‐treated MMT. Moreover, the results also show that the imidazolium‐modified clays have a greater thermal stability compared to the quinolinium and the pyridinium‐modified clay. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Montmorillonite with unique interlayer space imparted polymer scaffolds with sustained release of Ag+

Polyglycolic acid (PGA) has been a potential scaffold material due to its good biocompatibility and processibility, but its poor mechanical properties and over fast degradation restricted its application in bone repair. Meanwhile, it is worth noticing that bacterial infection is a common problem in bone repair. In this study, montmorillonite (MMT), with unique interlayer space, was introduced to PGA scaffolds prepared via additive manufacturing to address the problems. The results indicated MMT acted as rigid reinforcements dispersing well in the PGA matrix, which effectively transferred and absorbed the stresses in the matrix, thereby significantly increasing the compressive properties and hardness of the scaffolds. Moreover, MMT played the role of impermeable barriers in the matrix, hindering the diffusion of water and its attack on the matrix, which inhibited the hydrolysis and hence significantly decreased the degradable rate. More importantly, Ag⁺ was loaded into the interlayer space of MMT via ion exchange and was further chemically reduced to metallic Ag with higher stability. The impermeable layered structure of MMT presented dual barrier effects on the release of Ag⁺ via inhibiting the attack of water on Ag from outside and the diffusion of Ag⁺ from inside. Hence, the scaffolds exhibited a sustained Ag⁺ release and a long-lasting antibacterial property.     

Photochemical Synthesis of Silver Hydrosol Stabilized by Carbonate Ions and Study of Its Bactericidal Impact on Escherichia coli: Direct and Indirect Effects

The great attention paid to silver nanoparticles is largely related to their antibacterial and antiviral effects and their possible use as efficient biocidal agents. Silver nanoparticles are being widely introduced into various areas of life, including industry, medicine, and agriculture. This leads to their spreading and entering the environment, which generates the potential risk of toxic effect on humans and other biological organisms. Proposed paper describes the preparation of silver hydrosols containing spherical metal nanoparticles by photochemical reduction of Ag⁺ ions with oxalate ions. In deaerated solutions, this gives ~10 nm particles, while in aerated solutions, ~20 nm particles with inclusion of the oxide Ag₂O are obtained. Nanoparticles inhibit the bacterium Escherichia coli and suppress the cell growth at concentrations of ~1 × 10⁻⁶–1 × 10⁻⁴ mol L⁻¹. Silver particles cause the loss of pili and deformation and destruction of cell membranes. A mechanism of antibacterial action was proposed, taking into account indirect suppressing action of Ag⁺ ions released upon the oxidative metal dissolution and direct (contact) action of nanoparticles on bacterial cells, resulting in a change in the shape and destruction of the bacteria.     

Formulation of silver chloride/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (AgCl/PHBV) films for potential use in bone tissue engineering

Orthopedic implant failure due to bacterial infection has been a concern in bone tissue engineering. Here, we have formulated a composite made of biodegradable polymer, i.e., poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and silver chloride. Ag⁺ ions released from the AgCl/PHBV film can promote an aseptic environment by promoting inhibition of bacterial growth while maintaining bone cell growth, depending on AgCl loading. The objective of this study is to formulate AgCl/PHBV film(s) of varying composition so as to evaluate the dependence of AgCl loading in the film on antimicrobial activity and cytotoxicity. The release kinetics of silver ions from AgCl/PHBV film in aqueous and Dulbecco's Modified Eagle Medium showed similarity in the initial burst of ions during the first day of desorption followed by a gradual release of ions over extended time period. The antibacterial efficacy of AgCl/PHBV film against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa was evaluated by microbiological assay, while cytotoxicity of the film toward MC3T3‐E1 cells was determined by MTT assay. For all compositions studied, a clear zone of inhibition around AgCl/PHBV film was noticed on a modified Kirby‐Bauer disk diffusion assay. We established that MC3T3‐E1 cell attachment on AgCl/PHBV film is strongly related to loading of AgCl in the film. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45162.     

Formulation of epoxy–polyester powder coatings containing silver-modified nanoclays and evaluation of their antimicrobial properties

Current interest in antimicrobial coatings is driven by an urgent need for more effective strategies to control microbial infection. In this study, antimicrobial nanoclays were prepared by ion-exchange of sodium montmorillonite (MMT) with silver ions which have been previously reported to exhibit biocidal activity. The extent of ion-exchange achieved was estimated by X-ray photoelectron spectroscopy. The silver-modified nanoclay (AgMMT) fully inhibited growth of Gram-negative bacterium Escherichia coli DH5α (E. coli) over 24 h; annealing AgMMT under typical conditions used to prepare polymer composites did not reduce its antimicrobial efficacy. However, powder coatings of AgMMT dispersed in epoxy/polyester resin exhibited no antimicrobial effect on E. coli. This is believed to be caused by poor wetting of the polymer coating, which restricted the diffusion of silver ions from the coating.