Novel silver‐loaded semi‐interpenetrating polymer network gel films with antibacterial activity

Novel semi‐interpenetrating polymer networks (SIPNs) based on segmented polyurethane‐urea and poly(N‐isopropylacrylamide‐co‐acrylic acid‐co‐butylmethacrylate) (poly(NIPAM‐co‐AA‐BMA)) were synthesized for the fabrication of silver nanoparticles (AgNPs) in the SIPN system that could be useful for wound dressing applications. The obtained SIPN films, after neutralization, showed high swelling in aqueous environments and good mechanical properties in both dry and hydrated states. Analysis of the dried SIPN films by differential scanning calorimetry and dynamic viscoelastic measurements revealed the presence of crosslinked copolymers as well as homopolymers in the SIPN system. The neutralized swollen SIPN film coordinated with the silver ions (Ag⁺) that were incorporated into it. AgNPs were subsequently formed by the reduction of Ag⁺. The formation of AgNPs was characterized by UV‐visible spectroscopy, atomic force microscopy, wide‐angle X‐ray diffraction, and thermogravimetric analysis (TGA). Bactericidal activity tests revealed a distinct zone of microbial inhibition within and around the silver‐doped SIPN films. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4950–4962, 2009     

Probing Surface Enhancement Effect of Molecules On/Between Silver Nanoparticles in Surface Enhanced Raman Scattering

To explore the mechanisms in Surface‐enhanced Raman Scattering (SERS) measurements, silver nanoparticles (AgNPs) were first prepared by a silver mirror reaction to form different particle sizes and different distributions on glass substrates. After the resulting surfaces were probed with molecules of p‐Amino‐thiophenol (pATP), p‐Nitrothiophenol (pNTP), and p‐Mercaptobenzoic acid (pMBA) individually, the substrates were placed into reaction solutions to grow additional AgNPs. In this way, probe molecules could be trapped between two nanoparticles, possibly having the so‐called “hot spot” effect. To examine the variations of morphologies of AgNPs in each of the steps, the substrates were examined by field‐emission scanning electron microscope (FE‐SEM). The morphologies also were correlated with the SERS signals. Two bands in the SERS spectra of probe molecules were selected as indications of the enhancements from electromagnetic (EM) effect and charge‐transfer (CT). Results indicate that the SERS signals from the EM effect were increased ca. 5 times after growing additional AgNPs on the molecule‐modified AgNPs substrates. The SERS signals from CT effect were increased two orders of magnitude after growing additional AgNPs. The increase of enhancement for molecules between AgNPs was caused mostly by CT effect. Based on the effect of particle size and distribution of the AgNPs, the EM effect was strongly influenced by the particle size of the AgNPs, while the CT effect was less sensitive to the variation of the morphologies of the AgNPs.     

Nanocomposites based on crosslinked polyacrylic latex/silver nanoparticles for waterborne high‐performance antibacterial coatings

Functional polymer/AgNPs nanocomposites have been prepared. Silver nanoparticles (NPs) were synthesized to which polyacrylamide, PAAm, was covalently bound. PAAm was synthesized via a RAFT reaction and carried thiol and carboxylic acid end groups. Thiol was used to bind the polymer to the metal surface and carboxyl for further reactions. The AgNPs were used in a post‐crosslinking reaction with a separately synthesized poly(butyl acrylate‐co‐methyl methacrylate)/polyglycidyl methacrylate core/shell latex bearing epoxy functional groups. Dynamic mechanical analysis showed that the functional AgNPs effectively crosslinked the latex polymer, and that the final product had excellent mechanical strength. Antibacterial tests revealed that the nanocomposite films had strong antibacterial activity against all types of the bacteria and the immobilization of silver NPs by crosslinking retarded the release of silver in comparison to the uncrosslinked ones. With the presented method, it is possible to obtain ductile antibacterial nanocomposites to be used as waterborne functional coatings. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1435–1447     

The application of different Stevia rebaudiana leaf extracts in the “green synthesis” of AgNPs

ABSTRACT

The present work reports a method for green synthesis of silver nanoparticles (AgNPs) by reducing Ag ions from silver nitrate solution using alcoholic, aqueous and alcoholic-aqueous Stevia rebaudiana extracts. Depending on a particular extract different sizes of AgNPs could be observed – 40?nm in aqueous and aqueous-alcoholic extracts and significantly bigger 170?nm in case of alcoholic extract. Synthesis of AgNPs was analyzed within spectra range of 300–700?nm. The performed research provided information that aqueous and aqueous-alcoholic extracts are excellent sources for synthesis of AgNPs; however AgNPs were unstable in the case of alcoholic extract. The aqueous-alcoholic extract showed the best properties during studies. Antioxidant potential, antimicrobial properties and cytotoxicity were determined. The 2,2-diphenyl-1-(2,4,6-triphenyl-hydrazyl) method showed that antioxidant activity of an extract containing AgNPs was higher compared to Stevia extract alone. Bacterial inhibition studies had shown substantial antibacterial properties of AgNPs, which was much higher than Stevia extract alone and silver nitrate.     

Preparation and characterization by surface-enhanced infrared absorption spectroscopy of silver nanoparticles formed on germanium substrates by electroless displacement

In this paper, the feasibility of applying electroless displacement to prepare silver nanoparticles (AgNPs) on the surface of germanium (Ge) substrate is demonstrated, and the performances of surfaces prepared in this manner for surface-enhanced infrared absorption (SEIRA) spectroscopy are reported. The process used to produce suitable AgNPs for SEIRA by electroless deposition is simple and effective, requiring only pretreatment of the germanium surface with hot air, immersion of the substrate in a dilute solution of silver nitrate, and washing of the resulting plate. To quantify the behavior of AgNPs on a Ge substrate and to optimize the conditions for the preparation of AgNPs on Ge substrates, a monolayer of p-nitrothiophenol (PNTP) was bonded to the surface of the AgNPs by immersion of the plate in a dilute solution of PNTP and measurement of the transmission spectrum. The factors that influenced the formation of AgNPs, and hence the SEIRA signals, included the concentration of AgNO₃, the reaction time and the temperature. Results indicated that stronger absorption bands in the SEIRA spectrum of a monolayer of PNTP were obtained if the reaction rate for the displacement of silver ions by Ge was slow. This condition was achieved by keeping the concentration of AgNO₃ and the reaction temperature low. Under the optimal conditions found in this work, an enhancement factor of approximately 100 was achieved for commonly used probe molecules in SEIRA measurements.     

Modification of natural fibers from Thespesia lampas plant by in situ generation of silver nanoparticles in single-step hydrothermal method

Ligno-cellulosic fibers have a great market and propose higher value addition and options to develop various products but they do not have inherent antimicrobial properties. In this study, a simple hydrothermal method was applied to build up antimicrobial properties to natural fibers by in situ-generating silver nanoparticles (AgNPs) in them. Herein, the ligno-cellulosic Thespesia lampas natural fibers were selected to develop antimicrobial activity using silver nitrate (AgNO₃) solution by hydrothermal method. The modified fibers were characterized by SEM, FTIR, XRD, TGA, and antibacterial activity tests. The modified fibers had spherical AgNPs with an average size of 95?nm. The thermal stability of the modified fibers was higher than that of the unmodified fibers. The modified fibers exhibited good antibacterial activity against both the Gram negative and Gram positive bacteria. These modified fibers can be considered as fillers in polymer matrices to make antibacterial composites.     

Synthesis and antibacterial activity of surface‐coated catechol‐conjugated polymer with silver nanoparticles on versatile substrate

In the present study, 2‐chloro‐3′,4′‐dihydroxyacetophenone (CCDP), a catechol derivative, was quaternized with poly(propylene oxide)‐g‐poly(dimethylaminoethyl methacrylate) (PPO‐g‐PDMA, PgP) to prepare surface coatings for various substrates. The surfaces of noble metals, oxides, and synthetic polymers were coated by immersion in an aqueous solution of CCDP quaternized with PgP (C‐PgP). The catechol functional groups that remained on the surface were used for deposition of Ag nanoparticles (AgNPs) on the coated surface, to provide a water‐resistant antibacterial polymer with long‐term antimicrobial activity. X‐ray photoelectron spectroscopy confirmed deposition of C‐PgP and AgNPs on the surface coated with the antibacterial polymer. Surface‐immobilized C‐PgP/AgNPs showed outstanding antibacterial activities against Staphylococcus aureus, a Gram‐positive bacterium, and Escherichia coli, a Gram‐negative bacterium. C‐PgP/AgNPs can be applied to a variety of substrates and can therefore be used as antibacterial materials in various fields. Copyright © 2016 John Wiley & Sons, Ltd.     

Green synthesis and characterization of silver nanoparticles using Juniperus communis leaf extract: Catalytic activity in real-outdoor conditions and electrochemical properties

The present study investigates the green synthesis of stable silver nanoparticles using Juniperus communis leaf aqueous extract at room temperature. Synthesized silver nanoparticles (AgNPs) were characterized with different techniques such as UV–vis spectroscopy, Fourier transforms infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM-EDAX) and electrochemical method. Photocatalytic and anti-bacterial activities of synthesized AgNPs are evaluated based on the obtained result showed an efficient inhibition growth for gram negative P. Aeruginosa, E. Coli, and gram positive bacteria S.aureus. The AgNPs exhibited an excellent photocatalytic activity toward the degradation of methylene blue both indoor and outdoor, under sunlight, an efficiency of 95% was achieved. As an easy and environmentally friendly process, AgNPs based on Juniperus communis leaf extract could be applied for the degradation of pollutants and wastewater treatment.     

Coating of silver nanoparticles (AgNPs) on glass fibers by a chemical method as plasmonic surface-enhanced Raman spectroscopy (SERS) sensors to detect molecular vibrations of Doxorubicin (DOX) drug in blood plasma

In the present study, Doxorubicin (DOX) drug in healthy blood plasma was the focus of the investigation by surface-enhanced Raman scattering (SERS). In recent years, chemotherapy has been the most popular treatment for various types of cancer; however, its adverse side effects on the patient's health have made a negative aspect regarding the use of this technique. DOX is the most common chemotherapy drug and is used for the treatment of an extensive range of human malignancies. The surface-enhanced Raman scattering (SERS) is a precise technique for the detection of chemicals and biomaterials with significantly low concentrations. The glass fiber substrates coated with silver nanoparticles (AgNPs) have been used to detect DOX. First, the Tollens' method was applied to prepare the AgNPs, and the characteristics of fabricated AgNPs were evaluated using ultraviolet–visible spectroscopy (UV–Vis) and X-ray diffraction (XRD). Then, AgNPs were coated on the glass fiber substrate by a chemical method. Finally, the enhancement of the Raman signal resulted from the molecular vibrations of DOX was evaluated using these SERS-active substrates as plasmonic and Raman spectroscopy sensors. Afterward, for making the sensors practical, the DOX in blood plasma were deposited on the fabricated sensors, and the Raman vibrations were evaluated. The SERS-active substrates, AgNPs deposited on glass fiber substrates, were fabricated for the detection of DOX in and out of the blood plasma; the limit of detection (LOD) for both was 10^?10 M, and the mean relative standard deviation at concentrations of 10^?10 M of DOX out of blood plasma, and 10^?10 M of DOX in blood plasma were obtained to be 3.76% and 3.61%, respectively for ten repeated measurements in which the AgNPs were SERS-active substrates of the biosensors for detecting the DOX. In addition, the enhancement factor was calculated both experimentally and via finite-difference time-domain (FDTD) simulation, which was 29.76 × 10³ and 24.95 × 10³, respectively. Therefore, these SERS-active substrates can be used to develop microsensors and show positive results for SERS-based investigations.     

Immobilization of silver nanoparticles into POEGMA polymer brushes as SERS‐active substrates

Surface‐enhanced Raman scattering (SERS) has attracted a great deal of interest during the past four decades and emerged as an ultrasensitive optical technique for chemical and biomedical analysis. It is widely accepted that the facile fabrication of SERS substrates with high activity and good reproducibility is of crucial importance for their applications. Herein, we report on a fast and robust method for the synthesis and immobilization of silver nanoparticles (AgNPs) into poly(oligo(ethylene glycol) methacrylate) (POEGMA) brushes under mild conditions without using any reducing agents. POEGMA brushes of different chain lengths were synthesized directly on silicon wafers by surface‐initiated atom transfer radical polymerization with various reaction time. X‐ray photoelectron spectroscopy and field emission scanning electron microscope measurements indicated that the AgNPs were firmly and homogeneously embedded into POEGMA brushes. The resulting POEGMA–AgNP hybrid films were employed as SERS substrates for the detection of 4‐aminothiophenol, giving rise to an enhancement factor of up to 1.9 × 10⁶. The influence of the POEGMA's chain length on SERS performance was also investigated. Copyright © 2016 John Wiley & Sons, Ltd.     

A new green method for the synthesis of silver nanoparticles and their antibacterial activities against gram‐positive and gram‐negative bacteria

This study aims to evaluate the capability of Ageratum conyzoides and Mikania micrantha extracts to synthesize silver nanoparticles (AgNPs) and their antibacterial capability against gram‐positive and gram‐negative bacteria. Several properties of the synthesized AgNPs, including plasmonic, biomolecule bonding, shape, size, and antibacterial, were investigated. Ultraviolet–visible (UV–vis) spectroscopy was employed for characterizing their plasmonic properties. Functional groups on the produced AgNPs were investigated by Fourier‐transform infrared (FT‐IR) spectroscopy. The size and shape of the AgNPs were identified using the field‐emission scanning electron microscopy (FESEM). Inhibition zone measurement was carried out for evaluating the antibacterial capability. This study showed that the extracts of A. conyzoides and M. micrantha were able reducing agents as evidenced by the formation of the spherical AgNPs. UV–vis spectroscopy, FT‐IR spectroscopy, and FESEM confirmed the physicochemical characteristics of AgNPs. AgNPs that were synthesized using M. micrantha were slightly smaller than those produced using A. conyzoides. In general, the present work establishes that the synthesized AgNPs have antibacterial capability depending on their size and synthesis procedure.     

Design and synthesis of fluorescent core–shell nanoparticles with tunable lower critical solution temperature behavior and metal‐enhanced fluorescence

In this article, the preparation of fluorescent nanohybrids with core–shell structure and metal‐enhanced fluorescence (MEF) effect was presented. The fluorescent core–shell nanohybrids were prepared using silver nanoparticles (AgNPs) as cores and fluorophore tethered thermoresponsive copolymers with tunable lower critical solution temperature (LCST) from 15 to 90 °C as shells. These thermoresponsive copolymers were synthesized by the random copolymerization of oligo(ethylene oxide) acrylate and di(ethylene oxide) ethyl ether acrylate using reversible addition–fragmentation chain transfer polymerization and grafted on to AgNPs surface via Ag–S coordination interaction. By thermal manipulation of polymer spacer between AgNPs and fluorophores, the tunable MEF was achieved. It was also revealed that the fluorescent nanohybrids would exhibit maximal MEF when the polymerization degree was tuned to 350. The manipulation of the solution temperatures below and above LCST resulted in switchable MEF behavior. In addition, the phase transition process of the thermoresponsive copolymer was also studied by MEF effect using this fluorescent core–shell nanohybrid design. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 87–95     

Synthesis of amphiphilic graft copolymer brush and its use as template film for the preparation of silver nanoparticles

A microphase‐separated, amphiphilic graft copolymer consisting of a poly (vinyl chloride) (PVC) backbone and poly(oxyethylene methacrylate) (POEM) side chains, (PVC‐g‐POEM at 62:38 wt %) was synthesized via atom transfer radical polymerization (ATRP). Nuclear magnetic resonance (¹H NMR), FTIR spectroscopy, and transmission electron microscopy (TEM) clearly revealed that the “grafting from” method using ATRP was successful and that the graft copolymer molecularly self‐assembled into discrete nanophase domains of continuous PVC and isolated POEM regions. The self‐assembled graft copolymer film was used to template the growth of silver nanoparticles in solid state by introducing a AgCF₃SO₃ precursor and a UV irradiation process. The in situ formation of silver nanoparticles in the graft copolymer template film was confirmed by TEM, UV–visible spectroscopy, and wide angle X‐ray scattering. FTIR spectroscopy and X‐ray photoelectron spectroscopy also demonstrated the selective incorporation and in situ formation of silver nanoparticles within the hydrophilic POEM domains, presumably due to strong interactions between the silver and the ether oxygen in POEM. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3911–3918, 2008     

Synthesis of metal/polymer colloidal composites by the tailored deposition of silver onto porous polymer microspheres

A new colloidal silver system is presented in which a fine colloidal silver is in situ deposited onto functionalized porous poly(ethylene glycol dimethacrylate) [poly(EGDMA)] microspheres. The effectiveness of the silver deposition has been investigated through an examination of the surface characteristics of poly(EGDMA) microspheres. The result reported in this study demonstrate that the control of the surface area and surface functionality (in this study, a hydroxyl group) of poly(EGDMA) microspheres is an important factor that practically determines the degree of deposition of colloidal silver. X‐ray analysis has shown that silver nanoparticles are dispersed evenly on inner and outer surfaces and have a face center cubic phase. Preservation testing has shown that silver‐containing poly(EGDMA) microspheres have powerful antibacterial properties and, therefore, have significant potential as new preservatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2551–2557, 2004     

Daphne mucronata-mediated phytosynthesis of silver nanoparticles and their novel biological applications,compatibility and toxicity studies

This contribution reports the biosynthesis of silver nanoparticles (AgNPs) using aqueous leaf extracts of D. mucronata and their diverse applications. Synthesized AgNPs were characterized using diverse techniques, i.e. UV, XRD, EDS, SEM, TEM, FTIR and TGA/DTA. These techniques confirmed the authenticity of the synthesized nanoparticles. The bimodulated AgNPs revealed the highest radical scavenging potential, i.e. 86.4% relative to plant extract at 600?μg/ml. Escherichia coli was found to be the most susceptible strain to AgNPs. Growth of vancomycin-resistant Staphylococcus aureus was also inhibited. Hemolytic activity revealed negligible hemolysis, indicating the biocompatible nature of biomodulated AgNPs. Furthermore, no mutagenic properties were shown by the biogenic AgNPs. Synthesized nanoparticles possessed promising insecticidal potential and had no phytotoxic activity. No haemagglutination was observed for biogenic AgNPs.     

Silver Nanoparticle-Anchored Human Hair Kerateine/PEO/PVA Nanofibers for Antibacterial Application and Cell Proliferation

The main core of wound treatment is cell growth and anti-infection. To accelerate the proliferation of fibroblasts in the wound and prevent wound infections, various strategies have been tried. It remains a challenge to obtain good cell proliferation and antibacterial effects. Here, human hair kerateine (HHK)/poly(ethylene oxide) (PEO)/poly(vinyl alcohol) (PVA) nanofibers were prepared using cysteine-rich HHK, and then, silver nanoparticles (AgNPs) were in situ anchored in the sulfur-containing amino acid residues of HHK. After the ultrasonic degradation test, HHK/PEO/PVA nanofibrous mats treated with 0.005-M silver nitrate were selected due to their relatively complete structures. It was observed by TEM-EDS that the sulfur-containing amino acids in HHK were the main anchor points of AgNPs. The results of FTIR, XRD and the thermal analysis suggested that the hydrogen bonds between PEO and PVA were broken by HHK and, further, by AgNPs. AgNPs could act as a catalyst to promote the thermal degradation reaction of PVA, PEO and HHK, which was beneficial for silver recycling and medical waste treatment. The antibacterial properties of AgNP-HHK/PEO/PVA nanofibers were examined by the disk diffusion method, and it was observed that they had potential antibacterial capability against Gram-positive bacteria, Gram-negative bacteria and fungi. In addition, HHK in the nanofibrous mats significantly improved the cell proliferation of NIH3T3 cells. These results illustrated that the AgNP-HHK/PEO/PVA nanofibrous mats exhibited excellent antibacterial activity and the ability to promote the proliferation of fibroblasts, reaching our target applications.     

A surfactant‐free synthesis of the silica nanosphere‐supported ultrafine silver nanoparticles and their antibacterial effects

In this study, a facile, efficient, and surfactant‐free method to synthesize silica nanosphere‐supported ultrafine silver nanoparticles (AgNPs) (~2.5 nm) was developed, and their antibacterial effects were investigated. In the synthesis process, the hydrolysis of 3‐mercaptopropyltrimethoxysilane was adopted to provide thiol groups and in situ reduce Ag⁺ to Ag⁰ for ultrafine AgNPs formation on the surface of the silica nanosphere. Electron microscopy characterization of the complex formed revealed that the ultrafine AgNPs were not agglomerated and grow without any surfactants because there were no excess electrons transported from the shell to reduce the silver ions to silver atoms. The antibacterial effects of the supported ultrafine AgNPs with the surfactant‐free surface were evaluated against the Escherichia coli even at very low dosage. After incubation with 20 μg/mL silica‐supported AgNPs up to 120 min, 99.7% of the E. coli were inactivated, according to the bacterial viability measured by flow cytometry.     

Photochemical decoration of silver nanoparticles on magnetic microspheres as substrates for the detection of adenine by surface-enhanced Raman scattering

In this work, silver nanoparticles (AgNPs) decorated magnetic microspheres (MMs) are prepared as surface-enhanced Raman scattering (SERS) substrate for the analysis of adenine in aqueous solutions. To prepare these substrates, magnetic particles were first synthesized by coprecipitation of Fe(II) and Fe(III) with ammonium hydroxide. A thin layer of cross-linked polymer was formed on these magnetic particles by polymerization through suspension of magnetic particles into a solution of divinyl benzene/methyl methacrylate. The resulted polymer protected magnetic particles are round in shape with a size of 80 μm in diameter. To form AgNPs on these MMs, photochemical reduction method was employed and the factors in photochemical reduction method were studied and optimized for the preparation of highly sensitive and stable AgNPs on MMs substrates (abbreviated as AgMMs substrates). By dispersing the AgMMs in aqueous samples, cylindrical magnet was used to attract the AgMMs for SERS detections. The observed enhancement factor of AgMMs reached 7 orders in magnitude for detection of adenine with a detection limit approaching to few hundreds of nanomolar.     

Modification of agricultural waste tamarind fruit shell powder by in situ generation of silver nanoparticles for antibacterial filler applications

The tamarind fruit shell powder (TFSP) from agricultural waste was modified by in situ generation of silver nanoparticles (AgNPs) using the one-step hydrothermal method and characterized by SEM, EDX, FTIR spectral, XRD, and antibacterial tests. SEM analysis indicated the in situ generation of AgNPs with an average size of 90?nm. FTIR analysis proved no structural changes between unmodified and modified TFSP. XRD analysis indicated in situ generation of AgNPs in the modified TFSP. Further, the TFSP with in situ generated AgNPs inhibited the growth of bacteria and hence can be used as antibacterial low-cost filler in making biocomposites.     

Biogenic Synthesis of Silver Nanoparticles with High Antimicrobial and Catalytic Activities using Sheng Di Huang (Rehmannia glutinosa)

Silver nanoparticles (AgNPs) are widely sought after for a variety of biomedical and environmental applications due to their antimicrobial and catalytic properties. We present here a green and simple synthesis of AgNPs utilizing traditional Chinese medicinal herbs. The screening of 20 aqueous herb extracts shows that Sheng Di Huang (Rehmannia glutinosa) had the most promising potential in producing AgNPs of 30±6 nm, with narrow size distribution and high crystallinity. The antimicrobial activities of these AgNPs conducted on E. coli cells were found to be superior in comparison to poly(vinylpyrrolidone)-capped AgNPs synthesized using common chemical method. Additionally, the AgNPs obtained possess excellent catalytic performance in the reduction of 4-nitrophenol to 4-aminophenol. We compared the phytochemical and FTIR spectral analyses of the herb extract before and after synthesis, in order to elucidate the phytochemicals responsible for the reduction of Ag⁺ ions and the capping of the AgNPs produced.