Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Considerations using silver nitrate as a reference for in vitro tests with silver nanoparticles
(2016)
Most in vitro tests regarding the cellular toxicology of nanoparticulate metals compare particle to associated metal ion exposure. However. it is also a fact. that for example silver ions are reduced by sugars or transformed to silver chloride by chloride salts which are abundant components of cell culture media. These reactions are likely to either complicate or even invalidate comparisons between effects of ions and particles. Here. we present a fast and quantitative method to determine particle formation and numbers in different cell culture media with non-destructive small-angle X-ray scattering (SAXS). Silver nitrate with a concentration of25 (.Jg Ag mL -I was dissolved for up to 24 h at 37 'C in Dulbeccos Modified Eagle Medium (DMEM) with and without 10% fetal bovine serum (FBS) and a solution ofO-glucose (4.5 (.Jg mL -1). respectively. Silver nanopartides were observed in all Solutions after 5 min. The cell culture media displayed a limited particle-growth. FBS showed an effect on the polydispersity of the generated particles but after 5 min the overall particle size was nearly equal in FBS and non FBS supplemented medium. Particles in D-glucose were precipitating after 10 min. Particulate silver concentration was between 3 and 4 (.Jg mL -1 in both cell culture media (CCM). These results should be taken into account when performing silver ion-toxicity experiments in relevant media.
Due to its simplicity, speed and ability to obtain a particle number size distribution, single particle ICP-MS (spICP-MS) has emerged as an important tool for the analysis of nanoparticles (NPs). However, when NPs are suspended in a complex, unknown solution, matrix effects can occur affecting the instrument’s sensitivity. As a result, an over- or underestimation of the particle size is possible.
In this work, a proof-of-concept study of the combination of isotopic dilution analysis (IDA) and spICP-MS compensating for possible matrix effects is presented. As an example, an isotopically enriched 109Ag standard solution was added to silver NPs (Ag NP) suspensions. Different NP suspensions with mean particle diameters between 30 and 80 nm were chosen. The mixtures were analyzed using a quadrupole ICP-MS instrument. Both Ag isotopes (107Ag and 109Ag) were monitored during one experiment. The result show a good agreement with the diameters obtained using conventional spICP-MS.
In a second step, the Ag NPs were suspended in a simulated seawater matrix. Using conventional spICP-MS, a great reduction in the signal intensities and consequently in the particle sizes, was monitored. The application of the IDA-spICP-MS approach on these samples was able to obtain similar diameters compared to the samples without matrix.
A reversed phase high performance liquid chromatography coupled to an inductively coupled Plasma mass spectrometer (HPLC–ICP-MS) approach in combination with isotope dilution analysis (IDA) for the separation and parallel quantification of nanostructured and ionic silver (Ag) is presented. The main Focus of this work was the determination of the ionic Ag concentration. For a sufficient stabilization of the Ions without dissolving the nanoparticles (NPs), the eluent had to be initially optimized. The determined Ag ion concentration was in a good agreement with results obtained using ultrafiltration. Further, the mechanism of the NP separation in the HPLC column was investigated. Typical size exclusion effects were found by comparing results from columns with different pore sizes. Since the recovery rates decreased with increasing Ag NP size and large Ag NPs did not elute from the column, additional interactions of the particles with the stationary phase were assumed. Our results reveal that the presented method is not only applicable to Ag NPs, but also to gold and polystyrene NPs. Finally, IDA-HPLC-ICP-MS experiments in single particle mode were performed to determine the particle cut-off size. The comparison with conventional spICP-MS experiments resulted in a similar diameter and particle size distribution.
A reversed phase high performance liquid chromatography coupled to an inductively coupled plasma mass spectrometer (HPLC-ICP-MS) approach in combination with isotope dilution analysis (IDA) for the separation and parallel quantification of nanostructured and ionic silver (Ag) is presented. The main focus of this work was the determination of the ionic Ag concentration. For a sufficient stabilization of the ions without dissolving the nanoparticles (NPs), the eluent had to be initially optimized. The determined Ag ion concentration was in a good agreement with results obtained using ultrafiltration. Further, the mechanism of the NP separation in the HPLC column was investigated. Typical size exclusion effects were found by comparing results from columns with different pore sizes. Since the recovery rates decreased with increasing Ag NP size and large Ag NPs did not elute from the column, additional interactions of the particles with the stationary phase were assumed. Our results reveal that the presented method is not only applicable to Ag NPs, but also to gold and polystyrene NPs. Finally, IDA-HPLC-ICP-MS experiments in single particle mode were performed to determine the particle cut-off size. The comparison with conventional spICP-MS experiments resulted in a similar diameter and particle size distribution.
We report on the development of ultra-small core-shell silver nanoparticles synthesized by an up-scaled modification of the polyol process. It is foreseen to use these thoroughly characterized particles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. Small-angle X-ray scattering (SAXS) analysis reveal a narrow size distribution of the silver cores with a mean radius of RC = 3.0 nm and a distribution width of 0.6 nm. Dynamic light scattering (DLS) provides a hydrodynamic radius of RH = 10.0 nm and a PDI of 0.09. The particles’ surface is covered with poly(acrylic acid) (PAA) forming a shell with a thickness of 7.0 nm, which provides colloidal stability lasting for more than six months at ambient conditions. The PAA can be easily exchanged by biomolecules to modify the surface functionality. Replacements of PAA with glutathione (GSH) and bovine serum albumin (BSA) have been performed as examples. We demonstrate that the particles effectively catalyze the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride. With PAA as stabilizer, the catalytic activity of 436 ± 24 L g⁻¹ s⁻¹ is the highest reported in literature for silver nanoparticles. GSH and BSA passivate the surface substantially resulting in a catalytic activity of 77.6 ± 0.9 and 3.47 ± 0.50 L g⁻¹ s⁻¹, respectively.
Creating the Silver Standard: Development of a Silver Nanoparticle Reference Material using SAXS
(2017)
The utilization of silver nanoparticles in consumer related products has significantly increased over the last decade, especially due to their antimicrobial properties. Today they are used in a high variety of products, which ranges from food containers over children toys and textiles. Therefore, research on the toxicological potential of silver in a nanoscale form becomes increasingly important for a high amount of studies. Unfortunately the results of these studies are extremely diverse and do not lead to a consistent evaluation of the toxicity of silver nanoparticles. The central problem lies in the use of a wide range of silver nanoparticles, which show a broad size distribution. To overcome this problem we report on the synthesis of ultra-small silver nanoparticles and their quantitative characterization by small-angle X-ray scattering. The particles are highly stable and show no aggregation for more than six months. SAXS analysis via a Monte Carlo data evaluation procedure reveal a narrow size distribution of the silver cores with a mean volume weighted radius of 3.0 nm and a distribution width of 0.6 nm. Dynamic light scattering provides a hydrodynamic radius of 10.0 nm and a PDI of 0.09. The particles are stabilized with poly(acrylic acid) (PAA) forming a shell with a thickness of 7.0 nm. It is foreseen to use these thoroughly characterized particles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. As a first step the particles are used in the first world-wide inter-laboratory comparison of SAXS. This study reveals that SAXS shows highly reproducible results for particles in the sub-20 nm region independently on the type of instrument used. Furthermore, the stabilizing ligand PAA can be easily exchanged by biomolecules to modify the surface functionality. Replacements of PAA with glutathione (GSH) and bovine serum albumin (BSA) have been performed as examples. With this flexible system first applications regarding biological application in an artificial digestion procedure have been performed. Thereby the changes in size distribution and aggregation state were monitored by SAXS.
Ever since increasing a reaction’s yield while shortening the reaction time is the main objective in synthesis optimization. Microwave reactors meet these demands. In literature however their usage is under discussion due to claims of the existence of non-thermal effects resulting from the microwave radiation. Especially for nano-material syntheses it is of crucial importance to be aware of influences on the reaction pathway. Therefore, we compare ultra-small silver nanoparticles with mean radii of 3 nm, synthesized via conventional and microwave heating. We employed a versatile one-pot polyol synthesis of poly(acrylic acid) (PAA) stabilized silver nanoparticles, which display superior catalytic properties. No microwave specific effects in terms of particle size distribution characteristics, as derived by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS), are revealed. Due to the microwave reactor’s characteristics of a closed system, syntheses can be carried out at temperatures beyond the solvent’s boiling point. Particle formation was accelerated by a factor of 30 by increasing the reaction temperature from 200 °C to 250 °C. The particle growth process follows a cluster coalescence mechanism. A post-synthetic incubation step at 250 °C induces a further growth of the particles while the size distribution broadens. Thus, utilization of microwave reactors enables an enormous decrease of the reaction time as well as the opportunity of tuning the particles’ size. Possibly, decomposition of the stabilizing ligand at elevated temperatures results in reduced yields. A temperature of 250 °C and a corresponding reaction time of 30 s represent a compromise between short reaction times and high yields.
Over the last decade nanoparticles are progressively included in products of our daily life. Due to their antimicrobial properties, silver nanoparticles are used in a high variety of consumer products ranging from food containers over medicine and textiles. Therefore, research on the toxicological potential of nanosilver becomes increasingly important. This includes investigations concerning uptake, distribution and excretion of the particles. However, little attention was paid to changes of physical and chemical properties of the particles in the human body. One of the most important questions is if the particles can pass the digestion process without altering their shape and size. In this study we report on a versatile system of ultra-small silver nanoparticles with a mean volume weighted radius of 3.1 nm and a narrow size distribution width of 20%. The nanoparticles’ coating of poly (acrylic acid) can easily be exchanged by biocompatible ligands like albumin or glutathione. The particles are thoroughly characterized by small angle X-ray scattering (SAXS), DLS, IR and UV/Vis spectroscopy. We used the particles in an artificial digestion procedure which mimics the gastro-intestinal passage (Figure 1). Thereby the changes in the size distribution during the digestion process were analytically monitored by SAXS. Additionally, we used as food components oil, starch, skimmed milk powder and mixture thereof to provide a preferably realistic environment. Large aggregates of up to 56 nm were formed in the absence of food additives. In contrast, the presence of oil and starch limit the radii of aggregates to about 10 nm. Milk powder shows strong protective properties resulting in only small aggregates of 6 nm radii. Our results indicate that silver can indeed pass the digestion process in a nanoscale form depending on the nanoparticle coating and additional ingredients. These results have an impact on future toxicological considerations regarding silver nanoparticle-containing consumer products.
Silver nanoparticles are one of the most widespread consumer related nanoparticles worldwide. Since the particles show special optical and antibacterial properties they are used for a wide range of applications from biological investigations over medical applications and catalysis. Especially the outstanding question of applicable alternatives for catalysts in diverse reactions can be addressed with the design of versatile system of small silver nanoparticles. In this study we present the synthesis and application of ultra-small silver nanoparticles with a narrow size distribution (R = 3.1 nm, σ = 0.6 nm). The particles are thoroughly characterized by small angle X-ray scattering, dynamic light scattering and UV/Vis spectroscopy. As a representative test reaction the reduction of 4-nitrophenol to 4-aminophenol was chosen. The particles show a catalytic activity of (436 ± 24) L g-1 s-1, which is two orders of magnitude higher than for other silver particles in the literature. The particles surrounding shell, composed of poly(acrylic acid), provides the particles with a good accessibility for the reactants. Since the catalytic activity strongly depends on the surrounding ligand, the particles shell can also be exchanged by other ligands enabling a tuning of the catalytic activity to a desired value. This shows the high flexibility of this system which can also be applied for other catalytic reactions.
The breadth of applications of nanoparticles and the access to food-associated consumer products containing nanosized materials lead to oral human exposure to such particles. In biological fluids nanoparticles dynamically interact with biomolecules and form a protein corona. Knowledge about the protein corona is of great interest for understanding the molecular effects of particles as well as their fate inside the human body. We used a mass spectrometry-based toxicoproteomics approach to elucidate mechanisms of toxicity of silver nanoparticles and to comprehensively characterize the protein corona formed around silver nanoparticles in Caco-2 human intestinal epithelial cells. Results were compared with respect to the cellular function of proteins either affected by exposure to nanoparticles or present in the protein corona. A transcriptomic data set was included in the analyses in order to obtain a combined multiomics view of nanoparticle-affected cellular processes. A relationship between corona proteins and the proteomic or transcriptomic responses was revealed, showing that differentially regulated proteins or transcripts were engaged in the same cellular signaling pathways. Protein corona analyses of nanoparticles in cells might therefore help in obtaining information about the molecular consequences of nanoparticle treatment.