Dissolution Of Silver Nanoparticles Research Articles

Controlling the growth of uncapped silver nanoparticles on poly methacrylic acid nanospheres: The effect of polymer’s free surface on the antimicrobial properties

In this study, the control over the growth of uncapped silver nanoparticles on the surface of poly methacrylic acid nanospheres is presented. The pH of the growth medium and the size of the polymer nanospheres were studied as parameters in relation to the antimicrobial activity of the resulting structures against Escherichia coli and Staphylococcus aureus. Adjustment of the growth medium pH has a direct effect on the number of silver nanoparticles grown on the surface of the nanospheres, while the size of the nanospheres affects the resulting silver nanoparticle size distribution. The minimum bactericidal concentration was determined to 8 and 32 μg/mL against E. coli and S. aureus respectively, whereas the antimicrobial efficiency of the resulting nanospheres was enhanced in structures with increased free surface. Hence, the contribution of the as synthesized structures to the antimicrobial activity is attributed to the polymer’s ability to form stable suspensions in the aqueous bacterial growth medium, thus promoting the dissolution of silver nanoparticles to Ag cations with antimicrobial activity.

Electrochemical Mechanism of Oxidative Dissolution of Silver Nanoparticles in Water: Effect of Size on Electrode Potential and Solubility.

For the first time, an electrochemical mechanism of oxidative dissolution of silver nanoparticles in aqueous solutions is suggested and substantiated. The dissolution is caused by the occurrence of two interrelated electrochemical processes: (1) silver oxidation on a microanode and (2) oxygen reduction on a microcathode. According to the suggested model, the standard electrode potential of a nanoparticle decreases with a decrease in its size, which leads to an increase in the electromotive force of the oxidative dissolution of silver. A proportional dependence of the solubility of nanoparticles on their standard potential is revealed. An empirical equation is derived that relates the solubility of AgNPs to their electrode potential and size. In the course of oxidation, silver nanoparticles undergo aggregation with a gradual increase in the potential to the value characteristic of the bulk metal. This leads to the deceleration and practical cessation of the dissolution.

Nanoscale Hydrophobicity and Electrochemical Mapping Provides Insights into Facet Dependent Silver Nanoparticle Dissolution.

Metal or metallic nanoparticle dissolution influences particle stability, reactivity, potential fate, and transport. This work investigated the dissolution behavior of silver nanoparticles (Ag NPs) in three different shapes (nanocube, nanorod, and octahedron). The hydrophobicity and electrochemical activity at the local surfaces of Ag NPs were both examined using atomic force microscopy (AFM) coupled with scanning electrochemical microscopy (AFM-SECM). The surface electrochemical activity of Ag NPs more significantly affected the dissolution than the local surface hydrophobicity did. Octahedron Ag NPs with dominant surface exposed facets of {111} dissolved faster than the other two kinds of Ag NPs. Density functional theory (DFT) calculation revealed that the {100} facet elicited greater affinities toward H2O than the {111} facet. Thus, poly(vinylpyrrolidone) or PVP coating on the {100} facet is critical for stabilizing and prevent the {100} facet from dissolution. Finally, COMSOL simulations demonstrated consistent shape dependent dissolution as we observed experimentally.

Size Dependent Dissolution of Silver Nanoparticles in Human Monocytic/Macrophage-Like U937 Cells and Speciation by Single Particle-Inductively Coupled Plasma-Mass Spectrometry (SP-ICP-MS)

Various analytical methods have been employed to assess the nanoparticle (NP) toxicity and to better understand cell interactions. In this study, a rapid single particle – inductively coupled plasma – mass spectrometry (SP-ICP-MS) method is utilized to evaluate silver nanoparticle (AgNP) uptake by human monocytic/macrophage-like U937 cells. For this purpose, the cells were incubated with 40 nm and 70 nm AgNPs at 100 and 1000 ng mL−1 for 48 h. After cells were incubated with 40 nm and 70 nm AgNPs at the lower dosage (100 ng mL−1), the silver mass per cell was determined to be 1.5 ± 0.1 fg/cell (approximately 4 nanoparticles) and 3.6 ± 0.1 fg/cell (approximately 2 nanoparticles), respectively. Furthermore, for 100 ng mL−1 AgNP exposure, the results showed that silver was present both in the medium and in cell lysate only as AgNP. However, when cells were treated with 40 nm and 70 nm AgNPs at 1000 ng mL−1, approximately 10% and 40% of the total Ag concentration in cell lysate were AgNP and the rest was Ag+, while AgNP was the only species in the medium. The results show that 40 nm AgNP dissolved significantly more in cells compared to 70 nm AgNP. Moreover, ultracentrifugation, ICP-MS, and field emission scanning electron microscopy (FE-SEM) were employed with scanning transmission electron microscopy (STEM) to validate and confirm the SP-ICP-MS results.

Single-Particle Electrochemical Imaging Provides Insights into Silver Nanoparticle Dissolution at the Solution-Solid Interface.

Dissolution of nanoparticles is an environmental interfacial process that affects the transformation of nanoparticles. Understanding the dissolution processes of nanoparticles is important to predict their fate in the aquatic environment. However, studying nanoparticle dissolution kinetics is still challenging since dissolution is usually coupled with nanoparticle aggregation. Here, we probed the dissolution process of Ag nanoparticles at the single-particle level by surface plasmon resonance microscopy. The single-particle imaging capability enabled us to classify Ag nanoparticles, measure the dissolution dynamics of single nanoparticles, and correlate the aggregation size with oxidation activity. Moreover, we studied the dual effect of natural organic matter on the dissolution of Ag nanoparticles and validated this result with real natural freshwater. Our study provides new insights into the dissolution of Ag nanoparticles, and this technique can be extended for other nanomaterials to evaluate their fate in aquatic environments.

Dissolution of Silver Nanoparticles in Stratified Estuarine Mesocosms and Silver Accumulation in a Simple Planktonic Freshwater Trophic Chain

The increasing presence of nanomaterials in consumer products has led the scientific community to study the environmental fate of these contaminants of emerging concern. Silver nanoparticles, used mainly for their antibacterial properties, are among the most common nanomaterials. Understanding their transformations and interactions with living organisms, especially under environmentally relevant conditions that can modify metal bioavailability, is a crucial step in the study of their impacts on aquatic ecosystems. In the present study, citrate-coated silver nanoparticles (20 nm; 10 µg/L) were added to the surface freshwater layer of mesocosms simulating a stratified estuary. The investigation by dialysis of the nanoparticle dissolution showed that a large amount of total silver was found in the freshwater layer (and a very low amount in the seawater layer) and that 5–15% was in the form of dissolved silver. These results indicate that the halocline, separating fresh water from seawater, acted as a strong density barrier limiting the sedimentation of the nanoparticles. A simple trophic chain, composed of the freshwater alga Chlamydomonas reinhardtii and the invertebrate Daphnia magna, was used to determine silver bioavailability. This study suggests that citrate-coated silver nanoparticles do not significantly contribute to Ag accumulation by algae but may do so for invertebrates.

Role of ionic surfactants on the plasmonic oxidative dissolution of silver nanoparticles by ferric ions

Effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) on the optical sensing of AgNPs toward ferric ions were investigated spectrophotometrically in an aqueous media. Surface Plasmon resonance (SPR) intensity of AgNPs was decreases after addition of ferric ions at room temperature. CTAB and SDS, respectively, catalyzed and inhibited the oxidative dissolution rates of AgNPs. The redox reaction between AgNPs and Fe3+ ions proceeds through the complex formation. The reaction follows first-, and fractional-order kinetics with AgNPs and Fe3+ ions, respectively. CTAB catalytic role was explained with micellar pseudo-phase model, and associated parameters were estimated. The activation parameters (Ea, ΔH#, and ΔS#) were found to be 23.7 kJ/mol, 16.6 kJ/mol, −226 J/K/mol, and 16.5 kJ/mol, 13.5 kJ/mol, −238 J/K/mol for aqueous and CTAB assisted dissolution of AgNPs. SDS coordinated with Fe3+ through electrostatic interactions in pre-, and post-micellar region, which in turn reduces the electron gaining tendency of Fe3+, and overall rates of sensing reaction decreases.

Graphene oxide-silver nanoparticle hybrid material: an integrated nanosafety study in zebrafish embryos

This work reports an integrated nanosafety study including the synthesis and characterization of the graphene oxide-silver nanoparticle hybrid material (GO-AgNPs) and its nano-ecotoxicity evaluation in the zebrafish embryo model. The influences of natural organic matter (NOM) and a chorion embryo membrane were considered in this study, looking towards more environmentally realistic scenarios and standardized nanotoxicity testing. The nanohybrid was successfully synthesized using the NaBH4 aqueous method, and AgNPs (~ 5.8 nm) were evenly distributed over the GO surface. GO-AgNPs showed a dose-response acute toxicity: the LC50 was 1.5 mg L-1 for chorionated embryos. The removal of chorion, however, increased this toxic effect by 50%. Furthermore, the presence of NOM mitigated mortality, and LC50 for GO-AgNPs changed respectively from 2.3 to 1.2 mg L-1 for chorionated and de-chorionated embryos. Raman spectroscopy confirmed the ingestion of GO by embryos; but without displaying acute toxicity up to 100 mg L-1, indicating that the silver drove toxicity down. Additionally, it was observed that silver nanoparticle dissolution has a minimal effect on these observed toxicity results. Finally, understanding the influence of chorion membranes and NOM is a critical step towards the standardization of testing for zebrafish embryo toxicity in safety assessments and regulatory issues.

Simultaneous electrochemical detection of ciprofloxacin and Ag(I) in a silver nanoparticle dissolution: Application to ecotoxicological acute studies

The combination of the indiscriminate use of antibiotics such as ciprofloxacin (CIP) and the recent use of biocides such as silver nanoparticles (AgNPs) that are eventually disposed of in the environment can negatively impact on aquatic biota. This work aims to develop a simple electrochemical method to detect CIP, AgNPs, and their mixtures (CIP–AgNPs) concentrations and to correlate them with the ecotoxicological effects in acute toxicity bioassays (48 h) using the microcrustacean Ceriodaphnia dubia as a test organism. The simultaneous electrochemical detection of CIP and Ag(I) in AgNP dissolution was performed by square wave anodic stripping voltammetry (SWASV) using a bismuth film electrode (BiFE). The analytical performance in the linear range was from 8 to 200 ng L−1 (R2 = 0.993) for CIP and from 104 to 3300 ng L−1 (R2 = 0.995) for Ag(I). The limits of detection (LODs) were 3 and 34 ng L−1 for CIP and Ag(I), respectively. The method was applied to the measurements of Ag(I) in the supernatant of AgNP suspensions and the study of the stability of CIP and Ag(I) from AgNPs during acute tests of C. dubia at 48 h. The median lethal concentration (LC50) of C. dubia in the presence of CIP, AgNPs, and CIP–AgNPs was calculated, and the toxicity decreased as follows: AgNPs > CIP–AgNP mixture > CIP. The lower toxicity of AgNPs in mixture with CIP could be explained by the complexation of metal ions with quinolones, decreasing their interaction with the test organisms. The stabilities of CIP and Ag(I) from AgNPs in ecotoxicology assays were estimated by measuring their concentrations by SWASV, and their values ranged from 80% to 120% from the nominal values, according to the OECD recommendation. As a perspective, the results of the work showed that the simultaneous use of stripping voltammetry and toxicity tests could be applied to the study of natural water samples and potentially to the monitoring of environmental quality. The relevance of electrochemical and ecotoxicology approaches as useful tools to contribute knowledge to preserve environmental health is highlighted.

Effect of CTAB on the surface resonance plasmon intensity of silver nanoparticles: Stability and oxidative dissolution

Stable silver nanoparticles (AgNPs) were prepared from the reduction of silver ions by sodium borohydride in presence of shape controlling cationic cetyltrimethylammonium bromide (CTAB) at room temperature. The intensity and position of surface plasmon resonance (SRP), morphology depends on the concentrations of CTAB. The complex forming tendency of CTAB with positive head group of surfactant and borohydride anion (BH4−) was responsible for pre-, and post-micellar effect. The values of BH4−-CTAB binding constant (Ks = 33.6 × 104 mol−1 dm3) and rate constant in micellar pseudo phase (km = 5.5 × 10−5 s−1) were calculated. Catalytic role of CTAB discussed in term of pseudo-phase model. The silver soles were unstable at higher [BH4−] (≥14.0 × 10−5 mol/L). Transmission electron microscopic images indicate that the AgNPs are roughly spherical and poly dispersed. The oxidative dissolution of silver nanoparticles was very slow. The [BH4−] has significant impact on the sensing properties of AgNPs. The dissolution rate increases drastically by adding hydrogen peroxide. Scavengers quenched the oxygen radical reactive species (hydroxy radical and superoxide) and decreased the hydrogen peroxide catalyses rate of AgNPs.

Bovine Serum Albumin Enhances Silver Nanoparticle Dissolution Kinetics in a Size- and Concentration-Dependent Manner.

The dissolution of silver nanoparticles (AgNPs) to release Ag(I)(aq) is an important mechanism in potentiating AgNP cytotoxicity and imparting their antibacterial properties. However, AgNPs can undergo other simultaneous biophysicochemical transformations, such as protein adsorption, which can mediate AgNP dissolution behaviors. We report the comprehensive analysis of AgNP dissolution and protein adsorption behaviors with monolayer surface coverage of AgNPs by bovine serum albumin (BSA). AgNP dissolution rate constants, kdissolution, were quantified over several particle sizes (10, 20, and 40 nm) and BSA concentrations (0-2 nM) using linear sweep stripping voltammetry. Across all particle sizes, the dissolution rate constant increased with increasing BSA concentrations. However, protein-enhanced dissolution behaviors were most pronounced for 10 nm AgNPs, which exhibited 3.6-fold and 7.7-fold relative enhancement when compared to 20 and 40 nm AgNPs, respectively. Changes to AgNP surface properties upon interaction with BSA were monitored using dynamic light scattering and zeta potential measurements, while BSA-AgNP complex formation was evaluated using UV-vis spectroscopy and circular dichroism spectroscopy. A subtle increase in the BSA-AgNP association constant was observed with an increase in the AgNP size. Together, these results suggest that the AgNP size dependence of BSA-enhanced dissolution of AgNPs is possibly mediated through both displacement of Ag(I)(aq)-loaded BSA by excess protein in the bulk solution and minimized accessibility of the AgNP surface because of BSA adsorption.

Interaction of silver nanoparticles with antioxidant enzymes

This paper revealed that the changes in the protein conformation and the dissolution of silver nanoparticles depended on the protein structure and could result in different degrees of enzymatic activity modulation.

A comparative study of silver nanoparticle dissolution under physiological conditions.

Upon dissolution of silver nanoparticles, silver ions are released into the environment, which are known to induce adverse effects. However, since dissolution studies are predominantly performed in water and/or at room temperature, the effects of biological media and physiologically relevant temperature on the dissolution rate are not considered. Here, we investigate silver nanoparticle dissolution trends based on their plasmonic properties under biologically relevant conditions, i.e. in biological media at 37 °C over a period of 24 h. The studied nanoparticles, surface-functionalized with polyvinylpyrrolidone, beta-cyclodextrin/polyvinylpyrrolidone, and starch/polyvinylpyrrolidone, were analysed by UV-Vis spectroscopy, lock-in thermography and depolarized dynamic light scattering to evaluate the influence of these coatings on silver nanoparticle dissolution. Transmission electron microscopy was employed to visualize the reduction of the nanoparticle core diameters. Consequently, the advantages and limitations of these analytical techniques are discussed. To assess the effects of temperature on the degree of dissolution, the results of experiments performed at biological temperature were compared to those obtained at room temperature. Dissolution is often enhanced at elevated temperatures, but has to be determined individually for every specific condition. Furthermore, we evaluated potential nanoparticle aggregation. Our results highlight that additional surface coatings do not necessarily hinder the dissolution or aggregation of silver nanoparticles.

Fast dissolution of silver nanoparticles at physiological pH

While silver nanoparticles (AgNP) are used in topical treatments and medical devices for humans, no smooth, safe remedy exists to remove them and avoid possible post-treatment uptake in the body. We show here that cysteamine hydrochloride (CYS∙HCl), a simple FDA and EMA approved molecule, is able to dramatically accelerate the otherwise extremely slow oxidation of citrate-coated AgNP by O2 in a wide range of pH, including the physiological 7.4 value, obtaining the halving of AgNP concentration in t < 10 min. The dependence of oxidation kinetics on CYS concentration and pH is studied, finding faster processes on increasing CYS and basicity, despite the decrease of O2 reduction potential. Complexation and electrochemical studies demonstrate that CYS adhesion to AgNP surface followed by formation of 1:2 Ag+:CYS complex is the driving force for the AgNP oxidation, this also giving a definitive explanation to the otherwise still unclear phenomenon of AgNP etching by thiols. The efficacy of CYS∙HCl is verified also on AgNP coated with pectin and PEG-SH, and on AgNP immobilized on surfaces.

Real-time monitoring of the dissolution of silver nanoparticles by using a solid-contact Ag+-selective electrode

The dissolution kinetics of silver nanoparticles (Ag NPs) to Ag+ ions is a critical factor determining the toxicity of silver nanoparticles. In this work, a solid-contact Ag+-selective electrode (Ag+-ISE) is fabricated and used to monitor the dissolution of Ag NPs. Ordered mesoporous carbon is compared with disordered mesoporous carbon as the solid-contact material for the Ag+-ISE. The ordered mesoporous carbon based solid-contact Ag+-ISE shows a linear potential response in the range of 1.0 × 10−6-1.0 × 10−3 M AgNO3 with the slope of 55.6 ± 0.8 mV/dec (n = 7) and the detection limit of 10−6.8 M. The solid-contact Ag+-ISE is used to monitor the concentration changes of Ag+ during spontaneous dissolution of Ag NPs in deionized water, and the dissolution kinetics of Ag NPs is consistent with that obtained by inductively coupled plasma-mass spectrometry (ICP-MS). Stimulated dissolution of Ag NPs induced by addition of H2O2 to the Ag NP solution is also investigated by the proposed solid-contact Ag+-ISE. This work provides a fast tool for charactering the dissolution of Ag NPs to Ag+ in real time, which is important for studying the toxicology of nanoparticles.

Correction to: Oxidative dissolution of silver nanoparticles by synthetic manganese dioxide investigated by synchrotron X-ray absorption spectroscopy

Correction to: Oxidative dissolution of silver nanoparticles by synthetic manganese dioxide investigated by synchrotron X-ray absorption spectroscopy

Enhanced dissolution of silver nanoparticles in a physical mixture with platinum nanoparticles based on the sacrificial anode effect

A strategy to reduce implant-related infections is the inhibition of the initial bacterial implant colonization by biomaterials containing silver (Ag). The antimicrobial efficacy of such biomaterials can be increased by surface enhancement (nanosilver) or by creating a sacrificial anode system for Ag. Such a system will lead to an electrochemically driven enhanced Ag ion release due to the presence of a more noble metal. Here we combined the enlarged surface of nanoparticles (NP) with a possible sacrificial anode effect for Ag induced by the presence of the electrochemically more noble platinum (Pt) in physical mixtures of Ag NP and Pt NP dispersions. These Ag NP/Pt NP mixtures were compared to the same amounts of pure Ag NP in terms of cell biological responses, i.e. the antimicrobial activity against Staphylococcus aureus and Escherichia coli as well as the viability of human mesenchymal stem cells (hMSC). In addition, Ag NP was analyzed by ultraviolet–visible (UV–vis) spectroscopy, cyclic voltammetry, and atomic absorption spectroscopy. It was found that the dissolution rate of Ag NP was enhanced in the presence of Pt NP within the physical mixture compared to a dispersion of pure Ag NP. Dissolution experiments revealed a fourfold increased Ag ion release from physical mixtures due to enhanced electrochemical activity, which resulted in a significantly increased toxicity towards both bacteria and hMSC. Thus, our results provide evidence for an underlying sacrificial anode mechanism induced by the presence of Pt NP within physical mixtures with Ag NP. Such physical mixtures have a high potential for various applications, for example as antimicrobial implant coatings in the biomedicine or as bactericidal systems for water and surface purification in the technical area.

Oxidative dissolution of silver nanoparticles by synthetic manganese dioxide investigated by synchrotron X-ray absorption spectroscopy

Silver nanoparticles (AgNPs) are widely used in a variety of industrial and consumer applications and the disposal AgNP-containing materials is a potential source of environmental contamination. This study investigated the reaction of AgNPs with synthetic birnessite (δ-MnO2), a naturally-occurring MnO2 soil mineral shown in previous studies to oxidize both organic and inorganic dissolved species. The AgNPs used in this study ranged in size from 5 to 25 nm with an average particle diameter of 15.6 nm. Batch and kinetic reactions of MnO2-treated AgNP suspensions were studied by detecting AgNP oxidation to Ag+ using a combination of UV-Vis and microwave plasma atomic emission (MP-AES) spectrometries. Synchrotron K-edge X-ray absorption spectroscopy (XANES and EXAFS) was used to investigate the Ag oxidation state and structural characteristics of the reaction products. Oxidation of AgNP by MnO2 was detected in batch reactions showing an initial fast oxidation of AgNP to Ag+ (0–10 min) followed by a slower reaction (> 10 min) where Ag+ was removed by adsorption on MnO2 surfaces. XANES results confirmed that total AgNP oxidation by MnO2 occurred after 48 h when the Mn:Ag mole ratio treatment exceeded 5:1. The final AgNP oxidation product determined by EXAFS was Ag+ ion bound as a AgO4 tetrahedral structure in MnO2 interlayer cation exchange sites with Ag-O and Ag-Mn inter-atomic distances of 2.28 (± 0.02) and 3.88 (± 0.09) A, respectively. This structure is in agreement with previous EXAFS studies of naturally-occurring Ag-bearing MnO2 mineral samples and represents one of many possible Ag+ binding sites on soil mineral surfaces.

Long term impact of surfactants & polymers on the colloidal stability, aggregation and dissolution of silver nanoparticles

Cetyl trimethyl ammonium bromide (CTAB), Tween 20, polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) are among the commonly used surfactants and polymers to stabilize silver nanoparticles (AgNPs). However, their interactions with AgNPs are different. The impact of these surfactants and polymers on the colloidal stability of freshly synthesized uncoated AgNPs was evaluated through a series of long-term experiments and analyzed in terms of their physical and chemical behavior. The cationic surfactant, CTAB was able to produce a mono modal particle size distribution in a prolonged period without affecting the dissolution. In the presence of Tween 20, a non-ionic surfactant, dissolution was promoted in the long run and the particles were preserved with minimal aggregation. In the presence of the polymers, PVP and PEG, the particle structure was not affected even though dissolution was observed. This study presents important insights on the interactions of AgNPs with surfactants and polymers, which could significantly affect the transformations and fate of AgNPs in the aquatic environment.

Intracellular Dissolution of Silver Nanoparticles: Evidence from Double Stable Isotope Tracing.

To track transformations of silver nanoparticles (AgNPs) in vivo, HepG2 and A549 cells were cocultured with two enriched stable Ag isotopes (107AgNPs and 109AgNO3) at nontoxic doses. After enzymatic digestion, 107AgNPs, ionic 107Ag+ and 109Ag+ in exposed cells could be separated and quantified by liquid chromatography combined with ICP-MS. We found that ratios of 107Ag+ to total 107Ag and proportions of 107Ag+/ 109Ag+ in cells increased gradually after exposure, proving that the Trojan-horse mechanism occurred, i.e., AgNPs released high contents of Ag+ after internalization. While the presence of 109Ag+ (5 and 100 μg/L) has little influence on the uptake of 107AgNPs (0.1 and 2 mg/L), the presence of 107AgNPs at a high dose (2 mg/L) dramatically increases the ingestion of 109Ag+, even though 107AgNPs at a low dose (100 μg/L) showed negligible effects on the internalization of 109Ag+. Cellular homeostasis may be perturbed under sublethal exposure of 107AgNPs, and thus enhanced uptake of 109Ag+. Our findings suggest that the widely adopted control experiments in toxicology studies, culturing organisms with AgNO3 at the same concentration of Ag+ in the AgNP exposure medium, may underestimate uptake of Ag+ and thus cannot exclude suspected toxic effects of Ag+ at high AgNP exposure doses.