Polymer-stabilized Silver Research Articles

Polymer-Stabilized Silver (Gold)–Zinc Oxide Nanoheterodimer Structures as Antimicrobials

A simple one-pot method is proposed for obtaining the colloidal nanohybrid structures of silver (gold) and zinc oxide as well as nanostructures doped with zinc ions. The copolymers of maleic acid were used for the stabilization of nanoheterostructures. To characterize the preparation, UV–Vis spectroscopy, TEM, FTIR, XPS, and XRD were used. The bactericidal properties of the nanoheterostructures were studied in relation to the fungus C. albicans and the bacteria E. coli and S. aureus, used in planktonic form. In general, the samples containing nanosilver were the most active, and the preparations containing gold nanoparticles were the least active. The minimum inhibitory concentrations (MICs) of the Ag/ZnO samples, based on all copolymers, were in the ranges of 1.4–1.7 μg/mL for C. albicans, 2.9–6.8 μg/mL for E. coli, and 23–27 μg/mL for S. aureus; the MIC values of Au/ZnO samples were 472 μg/mL for S. aureus and 945 μg/mL for C. albicans and E. coli. The additional introduction of zinc cations into heterodimers had practically no effect on the antimicrobial properties of the composites. For all prepared composites and all tested microorganisms, the fractional inhibitory concentration indexes were in the range of 0.5–2.2, which indicates a close-to-additive contribution of the bioactive components in the samples used in the bactericidal process.

Protein coronas coating polymer-stabilized silver nanocolloids attenuate cytotoxicity with minor effects on antimicrobial performance

Silver nanoparticles are versatile platforms with a variety of applications in the biomedical field. In this framework, their presence in biological media inevitably leads to the interaction with proteins thus conducting to the formation of biomolecular coronas. This feature alters the identity of the nanomaterial and may affect many biological events. These considerations motivated the investigation of protein adsorption onto the surface of polymer-stabilized AgNPs. The metallic colloids were coated by polyethyleneimine (PEI), polyvinylpyrrolidone (PVP), and poly(2-vinyl pyridine)-b-poly(ethylene oxide) (PEO-b-P2VP), and nanoparticle-protein interaction was probed by using a library of analytical techniques. The experimental data revealed a higher extent of protein adsorption at the surface of AgNPs@PVP whereas PEO-b-P2VP coating conducted to the least amount. The main component of the protein coronas was evidenced to be bovine serum albumin (BSA), which is indeed the protein at the highest abundancy in the model biological media. We have further demonstrated reduced cytotoxicity of the silver colloids coated by biomolecular coronas as compared to the pristine counterparts. Nevertheless, the protein coatings did not notably reduce the antimicrobial performance of the polymer-stabilized AgNPs. Accordingly, although the protein-repelling property is frequently targeted towards longer in vivo circulation of nanoparticles, we herein underline that protein coatings, which are commonly treated as artifacts to be avoided, may indeed enhance the biological performance of nanomaterials. These findings are expected to be highly relevant in the design of polymer-stabilized metallic colloids intended to be used in healthcare.

Preparations Based on the Maleic Acid Copolymers Containing Silver Nanoparticles and Cations and Furan-2-Carboxylic Acid: Synthesis and Antituberculosis Activity

The complexes of silver ions with furan-2-carboxylic acid (Fur-COOH) and the conjugates of polymer-stabilized silver nanoparticles with silver cations and Fur-COOH are synthesized. The silver nanoparticles are studied by transmission electron microscopy (TEM), while the resulting conjugates—by UV–vis spectroscopy. All the objects obtained display prominent in vitro activity against the H37Rv strain of Mycobacterium tuberculosis. A synergistic effect of the silver components is revealed for the conjugates based on maleic acid-alt-N-vinylpyrrolidone containing nano- and cationic forms of silver, as well as Fur-COOH.

Surface-Oxidized Polymer-Stabilized Silver Nanoparticles as a Covering Component of Suture Materials.

In this work, we obtained silver nanoparticles stabilized with polyvinylpyrrolidone, ranging in size from 70 to 110 nm, which exhibits good crystallinity and anisotropic structure. For the first time, we studied the influence of the molar ratio of silver between silver and peroxide on the oxidation process of the nanoparticles and determined the regularities of this process by analyzing changes in absorption spectra. Our results showed that at molar ratios of Ag:H2O2 = 1:1 and 1:5, dependences of changes in the intensity, position and half-width of the absorption band of the plasmon resonance are rectilinear. In vivo studies of silver nanoparticles have shown that silver nanoparticles belong to the toxicity class III (moderately hazardous substance) and to the third group according to the degree of accumulation. We established that silver nanoparticles and oxidized silver nanoparticles form a uniform layer on the surface of the suture material. We found that the use of the suture material with silver nanoparticles and oxidized silver nanoparticles does not cause allergic reactions in the organisms of laboratory animals.

Evaluation of the Sorption Capacity of a Maleic Acid Copolymer Towards Gold(III) Ions and Production of Catalytically Active Gold Nanoparticles on Its Base

Two spectrophotometric approaches are suggested for the assessment of the concentration of gold(III) cations in an aqueous solution: direct recording of the optical density of gold cations and galvanic substitution of silver atoms in polymer-stabilized silver nanoparticles with gold cations. The sorption capacity of a maleic acid copolymer towards gold cations is estimated. A colloidal composite containing gold nanoparticles is obtained from the polymeric gold salt. The catalytic properties of the resulting polymer-stabilized nanogold are studied in the aerobic oxidation of glucose to gluconic acid.

Microfluidic-assisted synthesis of uniform polymer-stabilized silver colloids

We report the controlled synthesis of polymer-stabilized silver nanoparticles (AgNPs) by using microfluidic devices. The microfluidic-based method enabled the preparation of sub-50 nm AgNPs which are much more homogenous compared to those produced in batch reactors where the control over flow and mixing conditions was not performed. The concentration of the silver precursor (silver nitrate - AgNO3) can be tuned to reach smaller or larger nanoparticles, although within a fairly narrow range. Regardless of the polymeric shell, the reducing agent concentration influences the size and polydispersity of the manufactured silver colloids, and relatively lower amounts allow for the manufacturing of more homogeneous nanoparticles. Notably, the use of the block copolymer PEO-b-P2VP as stabilizing agent leads to larger nanoparticles (23–51 nm) compared to those stabilized by PVP (7–14 nm) as possibly linked to different arrangements of the polymer chains at the interface between the precursor solutions. The produced AgNPs are highly uniform, with size distribution width influenced by the polymer concentration (FWHM < 100 nm were determined at higher concentrations), although this variable does not have a distinguished effect on the final size of the manufactured colloids. Overall, we provide relevant new knowledge within the framework of polymer-stabilized AgNPs since a variety of other polymer chains can be probed, possibly with different outcomes regarding the final particle size. The reported findings can thus guide to significant advances towards the manufacturing of highly homogeneous polymer-coated metallic colloids, particularly when a target size is required.

Probing protein adsorption onto polymer-stabilized silver nanocolloids towards a better understanding on the evolution and consequences of biomolecular coronas.

The use of noble metal nanoparticles in biomedical and biotechnological applications is nowadays well established. Particularly, silver nanoparticles (AgNPs) were proven to be effective for instance as a biocide agent. They also find applications in tumor therapies and sensing applications being encouraging tools for in-vivo imaging. In this framework, whenever they are in contact with living systems, they are rapidly coated by a protein corona thereby influencing a variety of biological events including cellular uptake, blood circulation lifetime, cytotoxicity and, ultimately, the therapeutic effect. Taking these considerations into account, we have explored the behavior of polymer-coated AgNPs in model protein environments focusing on the self-development of protein coronas. The polymers polyethyleneimine (PEI), polyvinylpyrrolidone (PVP) and poly(2-vinyl pyridine)-b-poly(ethylene oxide) (PEO-b-P2VP) were used as stabilizing agents. The chemical nature of the polymer capping remarkably influences the behavior of the hybrid nanomaterials in protein environments. The PEO-b-P2VP and PVP-stabilized AgNPs are essentially inert to the model proteins adsorption. On the other hand, the PEI-stabilized AgNPs interact strongly with bovine serum albumin (BSA). Nevertheless, the same silver colloids were evidenced to be stable in IgG and lysozyme environments. The BSA adsorption into the PEI-stabilized AgNPs is most probably driven by hydrogen bonding and van der Waals interactions as suggested by isothermal titration calorimetry data. The development of protein coronas around the AgNPs may have relevant implications in a variety of biological events. Therefore, further investigations are currently underway to evaluate the influence of its presence on the cytotoxicity, hemolytic effects and biocide properties of the produced hybrid nanomaterials.

Preparation of silver nanoparticles with hyperbranched polymers as a stabilizer for inkjet printing of flexible circuits

Carboxyl-terminated hyperbranched polymer-stabilized silver nanoparticles were synthesized in the aqueous phase and used to prepare a printable conductive ink.

Nitrate and Nitrite Electrocatalytic Reduction at Layer-by-Layer Films Composed of Dawson-type Heteropolyanions Mono-substituted with Transitional Metal Ions and Silver Nanoparticles

A series of Dawson-type heteropolyanions (HPAs) mono-substituted with transitional metal ions (α2-[P2W17O61FeIII]8−, α2-[P2W17O61CuII]8− and α2-[P2W17O61NiII]8−) have exhibited electrocatalytic properties towards nitrate and nitrite reduction in slightly acidic media (pH 4.5). The immobilization of these HPAs into water-processable films developed via layer-by layer assembly with polymer-stabilized silver nanoparticles led to the fabrication of the electrocatalytic interfaces for both nitrate and nitrite reduction. The LBL assembly as well as the changes in the HPA properties by immobilization has been characterized by electrochemical methods. The effects of the substituent ions, outer layers and the cationic moieties utilized for the films assembly of the developed film on the performances of nitrate electrocatalysis has been elucidated.

Nanostructure of wet-chemically prepared, polymer-stabilized silver-gold nanoalloys (6 nm) over the entire composition range.

Bimetallic silver-gold nanoparticles were prepared by co-reduction using citrate and tannic acid in aqueous solution and colloidally stabilized with poly(N-vinylpyrrolidone) (PVP). The full composition range of silver : gold from 0 : 100 to 100 : 0 (n : n) was prepared with steps of 10 mol%. The nanoparticles were spherical, monodispersed, and had a diameter of ∼6 nm, except for Ag : Au 90 : 10 nanoparticles and pure Ag nanoparticles which were slightly larger. The size of the nanoalloys was determined by differential centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). By means of X-ray powder diffraction (XRD) together with Rietveld refinement, precise lattice parameters, crystallite size and microstrain were determined. Scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) showed that the particles consisted of a gold-rich core and a silver-rich shell. XRD and DCS indicated that the nanoparticles were not twinned, except for pure Ag and Ag : Au 90 : 10, although different domains were visible in the TEM. A remarkable negative deviation from Vegard's linear rule of alloy mixtures was observed (isotropic contraction of the cubic unit cell with a minimum at a 50 : 50 composition). This effect was also found for Ag:Au bulk alloys, but it was much more pronounced for the nanoalloys. Notably, it was much less pronounced for pure silver and gold nanoparticles. The microstrain was increased along with the contraction of the unit cell with a broad maximum at a 50 : 50 composition. The synthesis is based on aqueous solvents and can be easily scaled up to a yield of several mg of a well dispersed nanoalloy with application potential due to its tuneable antibacterial action (silver) and its optical properties for bioimaging.

Cellulose nanofibrils improve dispersibility and stability of silver nanoparticles and induce production of bacterial extracellular polysaccharides.

Many polymer-stabilized silver nanoparticles (AgNPs) with enhanced antibacterial properties have been synthesized, but very little is known about the fate of these materials and their interactions with microbes in physiological solutions. In this study, we evaluated the role of cellulose nanofibrils (CNFs) in stabilizing AgNPs (CNF-AgNPs) in a bacterial growth medium, determined the antibacterial properties of CNF-AgNPs and assessed the CNF and CNF-AgNP interactions with bacteria. The attachment of AgNPs to CNFs significantly improved the stability and dispersibility of AgNPs in the bacterial growth medium compared to colloidal AgNPs. The CNF-AgNPs exerted a concentration-dependent growth-inhibitory effect on E. coli. An extracellular polysaccharide (EPS)-like structure was formed around the E. coli bacterium when incubated with a sub-lethal CNF-AgNP concentration, which led to the clustering of neighboring bacteria. No EPS-like structure was observed around the bacterium incubated with high concentration of CNF-AgNPs. Overall, this study demonstrated that CNFs significantly improved the stability and dispersibility of AgNPs in physiological medium, validated the antimicrobial potential of CNF-AgNPs, and provided an insight into the physio-chemical interactions between bacteria and CNF-AgNPs in a physiological growth medium.

DNA-Stabilized Silver Nanoclusters with High Yield of Dark State Probed by Fluorescence Saturation Spectroscopy

Polymer-stabilized silver nanoclusters have gained much attention as a promising higly fluorescent biolabels [1]. While a wide palette of DNA-stabilized nanoclusters has been created, a little attention has been paid to their excited state properties. Meantime, dark long-lived non-emitting states have gained increasing interest in ultrahigh resolution microscopy, transient state imaging, and optically modulated microscopy [2] in the last years. The photoinduced dark states are used to be probed by pump-probe spectroscopy. However, it requires relatively high concentrations and it is not easily applied for heterogeneous samples.We applied fluorescence saturation spectroscopy for determining the photophysical constants of DNA-stabilized silver nanoclusters. This method allows one to determine the photophysical parameters of the ground and excited states such as absorption cross section, rate of intersystem crossing and others. Herein we report on extremely high yield of 25% of the dark state observed for the yellow-emitting Ag nanoclusters formed on calf thymus DNA [3]. This result seems to be promising in further creating polymer-stabilizing Ag nanoclusters with specially designed structure providing high efficiency of the dark state formation.[1] Obliosca, J. M.; Liu, C.; Batson, R. A.; Babin, M. C.; Werner. J. H.; Yeh, H.-C. DNA/RNA Detection Using DNA-Templated Few-Atom Silver Nanoclusters. Biosensors 2013, 3, 185-200.[2] Richards, C. I.; Hsiang, J.-C.; Senapati, D.; Patel, S.; Yu, J.; Vosch, T.; Dickson, R. M. Optically Modulated Fluorophores for Selective Fluorescence Signal Recovery. Journal of the American Chemical Society 2009, 131 (13), 4619-4621.[3] Volkov, I. L.; Ramazanov, R. R.; Ubyvovk, E. V.; Rolich, V. I.; Kononov, A. I.; Kasyanenko, N. A. Fluorescent Silver Nanoclusters in Condensed DNA. ChemPhysChem 2013, DOI: 10.1002/cphc.201300673.

Electrocatalytic activity of polymer-stabilized silver nanoclusters for hydrogen peroxide reduction

Silver nanoclusters (AgNCs) synthesized by using polyethyleneimine as a stabilizing scaffold have been confirmed as a novel material to exhibit high electrocatalytic activity for the reduction of hydrogen peroxide in this paper. The novel hydrogen peroxide electrochemical sensor was originally prepared based on the excellent electrocatalytic activity for the reduction of hydrogen peroxide at the polyethyleneimine-templated silver nanoclusters modified glassy carbon electrode (PEI/AgNCs–GCE). To achieve the optimum electrocatalytic activity for the reduction of hydrogen peroxide, the pH of the buffer solution and concentration of immobilizing AgNCs solution were optimized. Under optimum conditions, the PEI/AgNCs–GCE revealed a highly linear response to H2O2 in the concentration of 10–1440μmolL−1 with a detection limit of 1.8μmolL−1. Compared to some silver nanoparticles modified electrodes, the novel electrochemical sensor based on AgNCs exhibited a better electrocatalytic activity for the reduction of H2O2 and a lower detection limit for the determination of H2O2.

Toxicity Reduction of Polymer-Stabilized Silver Nanoparticles by Sunlight

The environmental and health impacts of nanomaterials are becoming important topics of research in recent years. The unique advantages offered by these nanomaterials in wide range of applications cannot be realized until these concerns are resolved. Among all the nanomaterials, Ag nanoparticles, due to their existing extensive uses in commercial products, demand immediate attention. Since the nanoparticle suspensions will be exposed to environmental conditions different from a research lab setting, many factors, including light, temperature, salinity, etc., are suspected to affect the stability of the nanoparticle and also their toxicity. In this study, we examined the effect of sunlight on the stability and toxicity of 6 and 25 nm Ag nanoparticles coated with gum arabic (GA) and polyvinylpyrrolidone (PVP). Under sunlight irradiation, all of these nanoparticles irreversibly aggregated to different degrees depending on the surface coating. The UV content of the sunlight is identified to be the driving force of nanoparticle aggregation, and the strong oscillating dipole−dipole interaction is believed to be the origin of the destabilization. Toxicity examinations of the nanoparticles to a wetland plant, Lolium multiflorum, indicate that their toxicity is greatly reduced after sunlight irradiation.

Green synthesis and characterization of polymer-stabilized silver nanoparticles

Silver nanoparticles (Ag-NPs) were synthesized using a facile green chemistry synthetic route. The reaction occurred at ambient temperature with four reducing agents introduced to obtain nanoscale Ag-NPs. The variables of the green synthetic route, such as acidity, concentration of starting materials, and molar ratio of reactants were optimized. Dispersing agents were employed to prevent Ag-NPs from aggregating. Advanced instrumentation techniques, such as X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible spectroscopy (UV–vis), and phase analysis light scattering technique (ZetaPALS) were applied to characterize the morphology, particle size distribution, elemental composition, and electrokinetic behavior of the Ag-NPs. UV–vis spectra detected the characteristic plasmon at approximately 395–410 nm; and XRD results were indicative of face-centered cubic phase structure of Ag. These particles were found to be monodispersed and highly crystalline, displaying near-spherical appearance, with average particle size of 10.2 nm using citrate or 13.7 nm using ascorbic acid as reductants from particle size analysis by ZetaPALS, respectively. The rapid electrokinetic behavior of the Ag was evaluated using zetapotential (from −40 to −42 mV), which was highly dependant on nanoparticle acidity and particle size. The current research opens a new avenue for the green fabrication of nanomaterials (including variables optimization and aggregation prevention), and functionalization in the field of nanocatalysis, disinfection, and electronics.

Thermoresponsive polymer-stabilized silver nanoparticles

Silver nanoparticles (Ag NPs) stabilized by a thermoresponsive polymer, poly( N-isopropylacrylamide) (PNIPAM), have been synthesized by the reduction of silver ions with NaBH 4 in aqueous solutions. The obtained Ag NPs are very stable at room temperature due to the extended coil conformation of the PNIPAM chain at temperatures below its volume phase transition temperature (∼32 °C). At higher temperatures (such as 45 °C) above the phase transition of PNIPAM, only minute aggregation between Ag NPs was observed, showing that the collapsed PNIPAM chains still retain the ability to stabilize Ag NPs. The PNIPAM-stabilized Ag NPs were then characterized as a function of the thermal phase transition of PNIPAM by UV–vis spectroscopy, dynamic light scattering, transmission electron microscopy, and cyclic voltammeter. Consistent results were obtained showing that the phase transition of PNIPAM has some effect on the optical properties of Ag NPs. Switchable electrochemical response of the PNIPAM-stabilized Ag NPs triggered by temperature change was observed.

Large-Scale Synthesis of Polymer-Stabilized Silver Nanoparticles

The synthesis and characterization of polymer-stabilized silver nanoparticles (Ag NPs) for water-based silver inks are studied. In order to synthesize Ag NPs with spherical shape, the conventional polyol processes require an excess of poly(vinyl pyrrolidone) (PVP) (10 ~ 1000 times than AgNO3) and therefore result in low productivity per reactor volume. In this study, poly(acrylic acid) (PAA) with carboxylic acid group was used instead of PVP. Even at less molar ratio of PAA to AgNO3 (&lt; 2), the spherical Ag NPs with average size of 30 nm were successfully synthesized at 100 gram-scale with high reaction yield of 90%. Furthermore, the Ag NPs were dispersed into alcohol-based solvent and then patterned into metallic lines through inkjet printing technology.