Addition Of AgNPs Research Articles

Development of a nanocomposite of polypropylene with biocide action from silver nanoparticles

ABSTRACTThis article presents the production of films based on blends of polypropylene (PP) and modified PP with the insertion of silver nanoparticles (AgNPs) produced to generate a bactericidal effect. The 50/50 blend of PP and PP modified by irradiation in acetylene at a dose of 12.5 kGy was processed in a twin‐screw extruder. The addition of AgNPs in poly(N‐vinyl‐2‐pyrrolidone) (PVP) solution was performed during processing in the extruder. The material was characterized by ultraviolet–visible spectroscopy, scanning electron microscopy, energy‐dispersive spectroscopy, transmission electron microscopy, cytotoxicity assay, and a reduction in colony‐forming units. The PP–PVP1% AgNP film showed silver particles in the nanoscale, presented no cytotoxicity for mammalian cells, and presented antimicrobial effects against Gram‐negativeEscherichia coliand Gram‐positiveStaphylococcus aureusbacteria. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2015,132, 42218.

Co-spinning of Silver Nanoparticles with Nisin Increases the Antimicrobial Spectrum of PDLLA: PEO Nanofibers.

Silver nanoparticles (AgNPs), synthesized using N,N-dimethylformamide (DMF), were electrospun with nisin in a 50:50 blend of 24% (w/v) poly(D,L-lactide) (PDLLA) and poly(ethylene oxide) (PEO). Addition of AgNPs decreased the average diameter of the nanofibers [silver nanofibers (SF)] from 588±191 to 281±64nm, or to 288±63nm when nisin was co-spun with AgNPs. Nanofibers containing AgNO3 (SF) had a beads-on-string structure, whereas nanofibers with AgNPs and nisin [silver plus nisin nanofibers (SNF)], nanofibers with only nisin [nisin nanofibers (NF)], and nanofibers without AgNPs and nisin [control nanofibers] had a uniform structure. The irregular topography was confirmed by atomic force microscopy. No interactions occurred between silver, nisin, PDLLA, and PEO, as confirmed with Fourier transform infrared spectroscopy. Most of the AgNPs (18±2.8ppm) and nisin (78.1±1.2µg/ml) were released within the first 2h. SF and SNF inhibited the growth of gram-positive and gram-negative bacteria, whereas NF failed to inhibit gram-negative bacteria. A wound dressing with broad-spectrum antimicrobial activity may be developed by the incorporation of nanofibers containing a combination of AgNPs and nisin.

Synthesis, characterization, optical and antimicrobial studies of polyvinyl alcohol–silver nanocomposites

Silver nanoparticles (Ag NPs) were synthesized by chemical reduction of silver salt (AgNO3) through sodium borohydride. The characteristic surface plasmon resonance band located at around 400nm in the UV–Visible absorption spectrum confirmed the formation of Ag nanoparticles. Polyvinyl alcohol–silver (PVA–Ag) nanocomposite films were prepared by the casting technique. The morphology and interaction of PVA with Ag NPs were examined by transmission electron microscopy and FTIR spectroscopy. Optical studies show that PVA exhibited indirect allowed optical transition with optical energy gap of 4.8eV, which reduced to 4.45eV under addition of Ag NPs. Optical parameters such as refractive index, complex dielectric constant and their dispersions have been analyzed using Wemple and DiDomenco model. Color properties of the nanocomposites are discussed in the framework of CIE L∗u∗v∗ color space. The antimicrobial activity of the nanocomposite samples was tested against Gram positive bacteria (Staphylococcus aureus NCTC 7447 &Bacillus subtillis NCIB 3610), Gram negative bacteria (Escherichia coli, NTC10416 &Pseudomonas aeruginosa NCIB 9016) and fungi (Aspergillus niger Ferm – BAM C-21) using the agar diffusion technique. The antimicrobial study showed that PVA has moderate antibacterial activity against B. subtillis and the 0.04wt% Ag NPs composite sample effect was strong against S. aureus.

Influence of silver nanoparticle addition, porosity, and processing technique on the mechanical properties of Ba0.3Co4Sb12 skutterudites

The thermoelectric skutterudite Ba0.3Co4Sb12 is a promising candidate for waste heat recovery applications. Recently, it was demonstrated that the addition of silver nanoparticles (AgNP) to Ba0.3Co4Sb12 increases both the thermoelectric figure of merit and electrical conductivity. This study is the first to examine the effect of AgNP addition on the material’s mechanical properties. This study also found that the Young’s modulus, E, shear modulus, G, and bulk modulus, B, decreased linearly with increasing volume fraction porosity, P. Resonant ultrasound spectroscopy was employed to measure the elastic moduli, and Vickers indentation was used to determine the hardness, H, and fracture toughness, K C. Trends in the mechanical properties as a function of grain size, porosity, and the AgNP are discussed in terms of the pertinent literature. While K C was independent of AgNP addition, porosity, and grain size, both E and H decreased linearly with increasing porosity. In addition, this study is the first to identify (i) the Ag3Sb phase formed and (ii) the enhanced densification that occurs when the AgNP is sintered with Ba0.3Co4Sb12 powders, where both effects are consistent with the eutectic and peritectic reactions observed in the binary phase diagram Ag–Sb. These eutectic/peritectic reactions may also be linked to the enhancement of electrical conductivity previously observed when Ag is added to Ba0.3Co4Sb12. Also, similar beneficial eutectic/peritectic reactions may be available for other systems where conductive particles are added to other antimonides or other thermoelectric systems.

Facile green synthesis of silver nanoparticles using seed aqueous extract of Pistacia atlantica and its antibacterial activity

In the present work, we describe the synthesis of silver nanoparticles (Ag-NPs) using seed aqueous extract of Pistacia atlantica (PA) and its antibacterial activity. UV–visible spectroscopy, X-ray diffraction (XRD), Fourier transform infra red spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray energy dispersive spectrophotometer (EDAX) were performed to ascertain the formation of Ag-NPs. It was observed that the growths of Ag-NPs are stopped within 35min of reaction time. The synthesized Ag-NPs were characterized by a peak at 446nm in the UV–visible spectrum. XRD confirmed the crystalline nature of the nanoparticles of 27nm size. The XRD peaks at 38°, 44°, 64° and 77° can be indexed to the (111), (200), (220) and (311) Bragg’s reflections of cubic structure of metallic silver, respectively. The FTIR result clearly showed that the extracts containing OH as a functional group act in capping the nanoparticles synthesis. Antibacterial activities of Ag-NPs were tested against the growth of Gram-positive (S. aureus) using SEM. The inhibition was observed in the Ag-NPs against S. aureus. The results suggest that the synthesized Ag-NPs act as an effective antibacterial agent. It is confirmed that Ag-NPs are capable of rendering high antibacterial efficacy and hence has a great potential in the preparation of used drugs against bacterial diseases. The scanning electron microscopy (SEM), indicated that, the most strains of S. aureus was damaged and extensively disappeared by addition of Ag-NPs. The results confirmed that the (PA) is a very good eco friendly and nontoxic source for the synthesis of Ag-NPs as compared to the conventional chemical/physical methods.

Eco-friendly synthesis of silver and gold nanoparticles with enhanced bactericidal activity and study of silver catalyzed reduction of 4-nitrophenol

The present study reports a simple and robust method for synthesis of silver and gold nanoparticles using Coleus forskohlii root extract as reducing and stabilizing agent. Stable silver nanoparticles (AgNPs) and gold nanopoarticles (AuNPs) were formed on treatment of an aqueous silver nitrate (AgNO3) and chloroauric acid (HAuCl4) solutions with the root extract. The nanoparticles obtained were characterized by UV–Visible spectroscopy, Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR). UV–Vis and TEM analysis indicate that with higher quantities of root extract, the interaction is enhanced leading to size reduction of spherical metal nanoparticles. XRD confirms face-centered cubic phase and the diffraction peaks can be attributed to (111), (200), (222) and (311) planes for these nanoparticles. These synthesized Ag and Au nanoparticles were found to exhibit excellent bactericidal activity against clinically isolated selected pathogens such as Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus). The synthesized AgNPs were also found to function as an efficient green catalyst in the reduction of anthropogenic pollutant 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride, which was apparent from the periodical color change from bright yellow to colorless, after the addition of AgNPs.

Study of energy transfer between riboflavin (vitamin B2) and AgNPs

Here, we report the studies on the interaction and formation of nanobiocomplex between silver nanoparticle (AgNPs) and vitamin B2, i.e., riboflavin (RF). The binding study of AgNP to RF was studied by fluorescence, UV–Vis, and TEM techniques. AgNPs were prepared by reducing AgNO3 with trisodium citrate. Prepared nanoparticles size obtained at 20 nm having surface Plasmon resonance band at 426 nm. The absorbance band of RF at 264, 374, and 444 nm changes significantly in the presence of AgNPs suggests that there is change in the chemical environment surrounding AgNPs. A fluorescence spectral change for a solution of RF upon the addition of AgNPs and rapid quenching is suggestive of a rapid adsorption of RF on AgNPs.

Transformation of aromatic dyes using green synthesized silver nanoparticles

Nowadays, increasing use of nanoproducts in area of human and environmental applications raises concern about safety aspects of nanoparticles synthesized using traditional physicochemical methods. Silver nanoparticles (AgNPs) synthesis at ambient parameters using latex of medicinally important plant Jatropha gossypifolia (J. gossypifolia) is reported in the present study. Potential of AgNPs in degradation of methylene blue and eosin B was also evaluated. Rapid formation of stable AgNPs was analyzed by visual color change from colorless to yellow-red after addition of latex in AgNO3 solution and by characteristic surface plasmon resonance (SPR) peak at 430 nm in UV-Vis spectroscopy. FT-IR analysis, protein coagulation test showed capping of proteins, flavonoids, terpenoids and polyphenols of latex on surface of AgNPs. FE-SEM, HR-TEM analysis revealed spherical shape of AgNPs. Narrow size range of AgNPs (5-40 nm) observed in HR-TEM analysis. EDS analysis confirms the presence of elemental silver while XRD revealed crystalline nature of AgNPs. Zeta potential of -21.4 mV indicates high stability of AgNPs. Effects of different parameters (pH, temperature, incubation time) on nanosynthesis were studied in the present study. Dye reduction studies were performed using UV-Vis spectroscopy, TLC, FT-IR and HPLC analysis showing decreased absorbance maxima of both dyes with respect to time, change in R f values, changes in wave number, transmittance, and retention time of dyes after AgNPs addition. The rate constant for methylene blue and eosin B reduction by AgNPs was found to be 0.062 and 0.022 min(-1).

Hybrid HPMC nanocomposites containing bacterial cellulose nanocrystals and silver nanoparticles

Hydroxypropyl methyl cellulose (HPMC) based hybrid nanocomposites reinforced with bacterial cellulose nanocrystals (BCNC) and silver nanoparticles (AgNPs) had been prepared and characterised. BCNC was capable of improving the tensile strength and modulus of HPMC, but they made the film more brittle. The addition of AgNPs along with BCNC, helped to regain some of the lost elongation properties without affecting other properties. Moisture sorption analysis proved that the hydrophilicity of the nanocomposite decreased considerably by the addition of these nanomaterials. Several mathematical models were also used to fit the experimental sorption results. A unique combination of two nanomaterials was highly effective in overcoming certain limitations of nanocomposites which uses only one type of nanomaterial. This type of hybrid nanocomposites with superior properties is expected to be useful in eco-friendly food packaging applications.

Dye-sensitized solar cells enhanced by optical absorption, mediated by TiO2 nanofibers and plasmonics Ag nanoparticles

Light harvesting in dye-sensitized solar cells (DSSCs) mediated by plasmonic metallic nanoparticles and sub-micron light-scattering metal oxides is a facile and cost-effective approach to achieving high device performance. Ag nanoparticles, protected by thin shells of TiO2, were incorporated in TiO2 photoanode. The large plasmonic near-field intensity generated by these nanoparticles caused an 18.3% rise in photocurrent, which resulted in an enhanced efficiency of 6.23% as compared to 5.29% efficiency of DSSC based on unmodified TiO2 photoanode. In addition, DSSC with TiO2 nanofibers (NFs) embedded in TiO2 photoanode was also constructed, which because of the efficient light scattering ability of the nanofibers, attained an efficiency of 7.14% as a result of a current rise of 36.9%. Another DSSC was assembled with Ag NPs added to the photoanode of the NFs-based DSSC to further boost cell performance. The addition of Ag NPs, however, did not produce an appreciable change in the cell performance. The reason for this unexpected outcome was probably due to the low internal resistance associated with charge recombination and large resistance to electron transport in the cell as determined by electrochemical impedance analysis computed in this work.

Transformation of PVP coated silver nanoparticles in a simulated wastewater treatment process and the effect on microbial communities

BackgroundManufactured silver nanoparticles (AgNPs) are one of the most commonly used nanomaterials in consumer goods and consequently their concentrations in wastewater and hence wastewater treatment plants are predicted to increase. We investigated the fate of AgNPs in sludge that was subjected to aerobic and anaerobic treatment and the impact of AgNPs on microbial processes and communities. The initial identification of AgNPs in sludge was carried out using transmission electron microscopy (TEM) with energy dispersive X-ray (EDX) analysis. The solid phase speciation of silver in sludge and wastewater influent was then examined using X-ray absorption spectroscopy (XAS). The effects of transformed AgNPs (mainly Ag-S phases) on nitrification, wastewater microbial populations and, for the first time, methanogenesis was investigated.ResultsSequencing batch reactor experiments and anaerobic batch tests, both demonstrated that nitrification rate and methane production were not affected by the addition of AgNPs [at 2.5 mg Ag L-1 (4.9 g L-1 total suspended solids, TSS) and 183.6 mg Ag kg -1 (2.9 g kg-1 total solids, TS), respectively].The low toxicity is most likely due to AgNP sulfidation. XAS analysis showed that sulfur bonded Ag was the dominant Ag species in both aerobic (activated sludge) and anaerobic sludge. In AgNP and AgNO3 spiked aerobic sludge, metallic Ag was detected (~15%). However, after anaerobic digestion, Ag(0) was not detected by XAS analysis. Dominant wastewater microbial populations were not affected by AgNPs as determined by DNA extraction and pyrotag sequencing. However, there was a shift in niche populations in both aerobic and anaerobic sludge, with a shift in AgNP treated sludge compared with controls. This is the first time that the impact of transformed AgNPs (mainly Ag-S phases) on anaerobic digestion has been reported.ConclusionsSilver NPs were transformed to Ag-S phases during activated sludge treatment (prior to anaerobic digestion). Transformed AgNPs, at predicted future Ag wastewater concentrations, did not affect nitrification or methanogenesis. Consequently, AgNPs are very unlikely to affect the efficient functioning of wastewater treatment plants. However, AgNPs may negatively affect sub-dominant wastewater microbial communities.

Synthesis, optimization, and characterization of silver nanoparticles from Acinetobacter calcoaceticus and their enhanced antibacterial activity when combined with antibiotics

BackgroundThe development of nontoxic methods of synthesizing nanoparticles is a major step in nanotechnology to allow their application in nanomedicine. The present study aims to biosynthesize silver nanoparticles (AgNPs) using a cell-free extract of Acinetobacter spp. and evaluate their antibacterial activity.MethodsEighteen strains of Acinetobacter were screened for AgNP synthesis. AgNPs were characterized using various techniques. Reaction parameters were optimized, and their effect on the morphology of AgNPs was studied. The synergistic potential of AgNPs on 14 antibiotics against seven pathogens was determined by disc-diffusion, broth-microdilution, and minimum bactericidal concentration assays. The efficacy of AgNPs was evaluated as per the minimum inhibitory concentration (MIC) breakpoints of the Clinical and Laboratory Standards Institute (CLSI) guidelines.ResultsOnly A. calcoaceticus LRVP54 produced AgNPs within 24 hours. Monodisperse spherical nanoparticles of 8–12 nm were obtained with 0.7 mM silver nitrate at 70°C. During optimization, a blue-shift in ultraviolet-visible spectra was seen. X-ray diffraction data and lattice fringes (d =0.23 nm) observed under high-resolution transmission electron microscope confirmed the crystallinity of AgNPs. These AgNPs were found to be more effective against Gram-negative compared with Gram-positive microorganisms. Overall, AgNPs showed the highest synergy with vancomycin in the disc-diffusion assay. For Enterobacter aerogenes, a 3.8-fold increase in inhibition zone area was observed after the addition of AgNPs with vancomycin. Reduction in MIC and minimum bactericidal concentration was observed on exposure of AgNPs with antibiotics. Interestingly, multidrug-resistant A. baumannii was highly sensitized in the presence of AgNPs and became susceptible to antibiotics except cephalosporins. Similarly, the vancomycin-resistant strain of Streptococcus mutans was also found to be susceptible to antibiotic treatment when AgNPs were added. These biogenic AgNPs showed significant synergistic activity on the β-lactam class of antibiotics.ConclusionThis is the first report of synthesis of AgNPs using A. calcoaceticus LRVP54 and their significant synergistic activity with antibiotics resulting in increased susceptibility of multidrug-resistant bacteria evaluated as per MIC breakpoints of the CLSI standard.

Biogenic robust synthesis of silver nanoparticles using Punica granatum peel and its application as a green catalyst for the reduction of an anthropogenic pollutant 4-nitrophenol

A robust synthesis of silver nanoparticles (AgNPs) using the peel extract of Punica granatum is reported in this article. The formation of AgNPs was confirmed by the appearance of brownish yellow color and the Surface Plasmon Resonance (SPR) peak at 432nm. The biogenic AgNPs were found to have the size approximately 30nm with distorted spherical shape. The high negative zeta potential values of AgNPs revealed their high stability which could be attributed to the capping of AgNPs by the phytoconstituents of the Punica granatum peel. The biogenic AgNPs were also found to function as an effective green catalyst in the reduction of anthropogenic pollutant viz., 4-nitrophenol (4-NP) by solid sodium borohydride, which was evident from the instantaneous color change of bright yellow (400nm) to colorless (294nm) solution, after the addition of AgNPs. The catalytic action of biogenic AgNPs in the reduction of 4-NP could be explained on the basis of Langmuir–Hinshelwood model.

Preparation and antibacterial properties of laser-generated silver–anatase nanocomposite film against Escherichia coli and Staphylococcus aureus

Anatase-based titanium dioxide (TiO2) naturally possesses a well recognized antibacterial effect under ultraviolet excitation. However, anatase modified with silver nanoparticles (Ag NPs) exhibits even stronger antibacterial action in natural daylight. The purpose of our present research is to evaluate the photocatalytic antibacterial effects of laser-generated silver–anatase nanocomposite film against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). A sol–gel TiO2 precursor was spin-coated on a clean glass slide and silver ions were self-adsorbed from aqueous solution. A pulsed beam of KrF excimer laser (248 nm, 13 ns) was traversed over the amorphous film, leading to the crystallization of the anatase and formation of cubic as well as hexagonal Ag NPs. A scanning transmission electron microscope analysis revealed a 30–40 nm anatase crystallite size, whereas an average size of 9.6 nm was obtained from Ag NPs. The photo-absorption of plain anatase was red-shifted to 516 nm with the addition of Ag NPs after the laser treatment. Moreover, no colonies of E. coli and S. aureus cells were observed to survive after 60 min of contact with the laser-modified silver–anatase films in the dark and in daylight conditions.

The production of polysulfone (PS) membrane with silver nanoparticles (AgNP): Physical properties, filtration performances, and biofouling resistances of membranes

The polysulfone (PS) membranes were prepared by adding different amounts of silver nanoparticle-AgNP (0–1wt%) into the dope solution. The bare PS and AgNP entrapped PS membranes (AgNP-PS composite membrane) were tested for physical properties with water permeability, MWCO (molecular weight cut-off), AFM, contact angle and SEM analyses, filtration performances by using the model protein (BSA) and carbohydrate (dextran) solutions and biofouling resistances by using a real activated sludge. AgNP addition improved the protein and carbohydrate filtration performances of bare PS membrane. The results of biofouling experiments showed the AgNP-PS composite membranes having lower absorptive and pore fouling values than bare PS membrane. The ionic silver loss from membrane during pure water filtration was measured using inductive-coupled plasma spectrometer (ICP) and the results showed the minimum silver loss from the composite membranes. The results of disk diffusion test showed that the composite AgNP-PS membranes decreased the growth of bacterial colonies. However PCR-DGEE technique showed that there were not significant differences in microbial community population density along the bare and composite membranes.

Genotoxicity and effects of nanosilver contamination in drinking water disinfection

This study was conducted to examine the genotoxicity and the influence of silver nanoparticles (AgNPs) contamination when drinking water is exposed to five different disinfection treatments: chlorine, chlorine dioxide, ozone, ozone/chlorine and ozone/chlorine dioxide. Experiments were conducted with water samples of different chemical composition, from three water supply systems in Croatia. AgNPs are of interest because of their use as an antimicrobial in numerous commercial products, and as a drinking water disinfection agent. To examine possible effects of AgNP contamination, the disinfection treatments were repeated with AgNPs in the water samples. AgNP contamination generally caused a decrease in the level of trihalomethanes by up to 59%. Influence of AgNPs on bromide ion incorporation into disinfection by-products (DBPs) was also examined. The most obvious example was the Osi water where ozonation step prior to chlorination increased the bromine incorporation factor from 0.156 to 0.339, while addition of AgNPs limited the increase to 0.249. Also, AgNP presence in almost all disinfection treatments increased dicarbonyl disinfection by-products. All treated waters were tested for genotoxicity using the comet assay and showed similar genotoxic potential. The results are preliminary, but could provide a basis for further studies evaluating the environmental impact of AgNPs in natural aquatic systems.

Interaction of silver nanoparticles with pure nitrifying bacteria

In this study, Nitrosomonas europaea ATCC 19718 was exposed to silver nanoparticles (AgNPs) of different particle size (7±3 and 40±14nm) and different coatings (polyvinyl alcohol and adenosine triphosphate disodium). For all different AgNPs used in the study, large aggregates were gradually formed after addition of AgNPs into the media containing N. europaea. The scanning electron microscopy and energy dispersive X-ray spectroscopy of the microstructures suggested that bacterial cells and electrolytes had significant effects on AgNP aggregation. Size- and coating-dependent inhibition of ammonia oxidation by AgNPs was observed, and our analysis suggested that the inhibition was not only due to the released dissolved silver, but also the dispersity of AgNPs in the culture media. Electron microscopy images showed AgNPs could cause the damage of cell wall of N. europaea and make the nucleoids disintegrated and condensed next to cell membrane. Surface-enhanced Raman scattering signals also implied the damage of cell membrane caused by AgNPs. Further protein expression analysis revealed that AgNPs would inhibit important protein functions, including biosynthesis, gene expression, energy production and nitrification to further cause toxicity to N. europaea. Our findings explain the susceptibility of N. europaea to inhibition by AgNPs and the possible interaction between each other. Future research is needed to characterize these effects in more complex cultures and media such as activated sludge and wastewater.

Preparation of Ag nanoparticle dispersed silk fibroin compact

We prepared a silk fibroin compact in which Ag nanoparticles (Ag NPs) were dispersed, by adding only silver nitrate (AgNO3) to a silk fibroin solution without using any reducing agent. FT-IR and DSC revealed that the formation of Ag NPs distorted the conformation of the silk fibroin. However, the Ag NPs did not affect the thermal stability of the silk fibroin compact. An antimicrobial test against Escherichia coli (E. coli) was performed using the silk fibroin compact in which Ag NPs were dispersed. The compact showed sufficient antimicrobial activity because the average survival of E. coli was 1.6% after 8h incubation even when the silver content was 0.01wt%. The addition of Ag NPs into silk fibroin compact can provide color and an antimicrobial function without spoiling the function of the silk fibroin compact.

Antimicrobial effects of commercial silver nanoparticles are attenuated in natural streamwater and sediment

Given the demonstrated antimicrobial properties of silver nanoparticles (AgNPs), and the key role that microorganisms play in performing critical ecosystem functions such as decomposition and nutrient cycling, there is growing concern that AgNP pollution may negatively impact ecosystems. We examined the response of streamwater and sediment microorganisms to commercially available 21 ± 17 nm AgNPs, and compared AgNP impacts to those of dissolved-Ag added as AgNO(3). We show that in streamwater, AgNPs and AgNO(3) decreased respiration in proportion to dissolved-Ag concentrations at the end of the incubation (r(2) = 0.78), while in sediment the only measurable effect of AgNPs was a 14 % decrease in sulfate concentration. This contrasts with the stronger effects of dissolved-Ag additions in both streamwater and sediment. In streamwater, addition of dissolved-Ag at a level equivalent to the lowest AgNP dose led to respiration below detection, a 55 % drop in phosphatase enzyme activity, and a 10-fold increase in phosphate concentration. In sediment, AgNO(3) addition at a level equivalent to the highest AgNP addition led to a 34 % decrease in respiration, a 55 % increase in microbial biomass, and a shift in bacterial community composition. The results of this study suggest that, in similar freshwater environments, the short-term biological impacts of AgNPs on microbes are attenuated by the physical and chemical properties of streamwater and sediment.

Therapeutic Window of Ligand‐Free Silver Nanoparticles in Agar‐Embedded and Colloidal State: In Vitro Bactericidal Effects and Cytotoxicity

AbstractThe inhibition of bacterial growth through effective non‐toxic antimicrobial substances is of great importance for the prevention and therapy of implant infections in various medical disciplines. For the evaluation of a therapeutic window of silver nanoparticles (AgNPs), their bactericidal properties were tested in agar composites and colloids on four medical relevant bacteria. Therefore, we produced AgNPs using high‐power nanosecond laser ablation in water showing a log‐normal particle diameter distribution centered at 17 nm. Bacteria were incubated with AgNP concentrations ranging from 5 to 70 µg · mL−1 and the growth rate was recorded. Additionally, cytotoxic effects of AgNPs on human gingival fibroblasts were examined. The experiments demonstrated that laser‐synthesized AgNPs resulted in a significant bacterial growth inhibition of more than 80% at the indicated concentrations in a solid agar model (Pseudomonas aeruginosa 10 µg · mL−1, Streptococcus salivarius 10 µg · mL−1, Escherichia coli 20 µg · mL−1, Staphylococcus aureus 70 µg · mL−1). In a planktonic bacteria model, the growth of the tested bacteria was significantly delayed by the addition of AgNPs at a concentration of 35 µg · mL−1. The cytotoxic assays showed limited adverse effects on human fibroblasts at concentrations of less than 20 µg · mL−1. The present study illustrates the strong antibacterial effects of ligand‐free, laser‐generated AgNPs that exhibit moderate cytotoxic effects, resulting in a therapeutically applicable concentration of AgNPs for medical purposes between 10 and 20 µg · mL−1.