Development and validation of single particle ICP-MS for sizing and quantitative determination of nano-silver in chicken meat

The application of nanomaterials is leading to innovative developments in industry, agriculture, consumer products, and food and related sectors. However, due to the special properties of these materials there are concerns about their safety, especially because of our limited knowledge of human health effects and the fact that constantly new nanomaterials and applications thereof are being produced. The development of analytical techniques is a key element to understand the benefits as well as the risks of the application of such materials. In this study, a method is developed and validated for sizing and quantifying nano-silver in chicken meat using single particle inductive coupled plasma mass spectrometry (ICP-MS). Samples are processed using an enzymatic digestion followed by dilution of the digest and instrumental analysis of the diluted digest using single particle ICP-MS. Validation of the method in the concentration of 5–25 mg/kg 60-nm silver nanoparticles showed good performance with respect to trueness (98–99 % for size, 91–101 % for concentration), repeatability (<2 % for size, <11 % for concentration), and reproducibility (<6 % for size, <16 % for concentration). The response of the method is linear, and a detection limit as low as 0.1 mg/kg can be obtained. Additional experiments showed that the method is robust and that digests are stable for 3 weeks at 4 °C. Once diluted for single particle ICP-MS analysis, the stability is limited. Finally, it was shown that nano-silver in chicken meat is not stable. Silver nanoparticles dissolved and were transformed into silver sulfide. While this has implications for the form in which nano-silver will be present in real-life meat samples, the developed method will be able to determine the presence and quantity of nanoparticle silver in such samples.     

Measuring silver nanoparticle dissolution in complex biological and environmental matrices using UV-visible absorbance

Distinguishing the toxic effects of nanoparticles (NPs) themselves from the well-studied toxic effects of their ions is a critical but challenging measurement for nanotoxicity studies and regulation. This measurement is especially difficult for silver NPs (AgNPs) because in many relevant biological and environmental solutions, dissolved silver forms AgCl NPs or microparticles. Simulations predict that solid AgCl particles form at silver concentrations greater than 0.18 and 0.58 μg/mL in cell culture media and moderately hard reconstituted water (MHRW), respectively. The AgCl NPs are usually not easily separable from AgNPs. Therefore, common existing total silver techniques applied to measure AgNP dissolution, such as inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption, cannot accurately measure the amount of silver remaining in AgNP form, as they cannot distinguish Ag oxidation states. In this work, we introduce a simple localized surface plasmon resonance (LSPR) UV–visible absorbance measurement as a technique to measure the amount of silver remaining in AgNP form for AgNPs with constant agglomeration states. Unlike other existing methods, this absorbance method can be used to measure the amount of silver remaining in AgNP form even in biological and environmental solutions containing chloride because AgCl NPs do not have an associated LSPR absorbance. In addition, no separation step is required to measure the dissolution of the AgNPs. After using ICP-MS to show that the area under the absorbance curve is an accurate measure of silver in AgNP state for unagglomerating AgNPs in non-chloride-containing media, the absorbance is used to measure dissolution rates of AgNPs with different polymer coatings in biological and environmental solutions. We find that the dissolution rate decreases at high AgNP concentrations, 5 kDa polyethylene glycol thiol coatings increase the dissolution rate, and the rate is much higher in cell culture media than in MHRW.     

Evaluation of a cloud point extraction method for the preconcentration and quantification of silver nanoparticles in water samples by ETAAS

ABSTRACT

A simple and reliable analytical method using instrumentation available in most of the laboratories has been developed for the separation and determination of silver nanoparticles in water samples. Cloud point extraction (CPE) was used for the separation of silver nanoparticles (AgNPs) from the sample and these nanoparticles were then determined by electrothermal atomic absorption spectrometry (ETAAS). Parameters related to the cloud point extraction procedure (Triton X-114 concentration, type of complexing agent (EDTA or Na₂S₂O₃), pH, incubation temperature, incubation and centrifugation time) were selected using a multivariate approach (designs of experiments); 8.6% (v/v) Triton X-114, 750 µL saturated EDTA and pH 7 were selected as the optimum conditions. Calibration standards in a concentration range from 0 to 10 µg L^?1 of AgNPs were subjected to the CPE procedure to obtain quantitative recoveries. The LOD and LOQ were 0.04 and 0.13 µg L^?1, respectively. The method is selective for the extraction of AgNPs, and ionic Ag remains in the aqueous phase. Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) was used to evaluate the effect of the CPE procedure in particle size, and no changes were observed. Finally, the procedure was applied to wastewater samples spiked with nanoparticles with quantitative recoveries.     

不同水环境对纳米银颗粒聚集体粒径大小及界面电势的影响

研究了不同水环境对无稳定剂与PVP为稳定剂的纳米银颗粒的物化性能的影响。结果表明:随着电解质浓度的增加,纳米银颗粒的粒径与界面电势逐步增大;二价阳离子比一价阳离子更能有效地使纳米银粒径与界面电势增加;稳定剂PVP,腐植酸及其他天然有机物能够增加纳米银溶胶的稳定性;在天然水体中,纳米银在海水中的粒径颗粒与界面电势比湖水中更大。     

Size characterization and quantification of silver nanoparticles by asymmetric flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry

A method for determining the size of silver nanoparticles and their quantification by asymmetric flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry (ICP-MS) is proposed and was tested in consumer products. Experimental conditions were studied in detail to avoid aggregation processes or alteration of the original size distributions. Additionally, losses from sorption processes onto the channel membrane were minimized for correct quantification of the nanoparticles. Mobile phase composition, injection/focusing, and fractionation conditions were evaluated in terms of their influence on both separation resolution and recovery. The ionic strength, pH, and the presence of ionic and nonionic surfactants had a strong influence on both separation and recovery of the nanoparticles. In general, better results were obtained under those conditions that favored charge repulsions with the membrane. Recovery values of 83 ± 8% and 93 ± 4% with respect to the content of silver nanoparticles were achieved for the consumer products studied. Silver nanoparticle standards were used for size calibration of the channel. The results were compared with those obtained by photon correlation spectroscopy and images taken by transmission electron microscopy. The quantification of silver nanoparticles was performed by direct injection of ionic silver standard solutions into the ICP-MS system, integration of the corresponding peaks, and interpolation of the fractogram area. A limit of detection of 5.6 μg L^-1 silver, which corresponds to a number concentration of 1×10¹² L^-1 for nanoparticles of 10 nm, was achieved for an injection volume of 20 μL.     

Potential of Kalopanax septemlobus Leaf Extract in Synthesis of Silver Nanoparticles for Selective Inhibition of Specific Bacterial Strain in Mixed Culture

Silver nanoparticles (AgNPs) were synthesised using Kalopanax septemlobus plant leaf extracts. UV-visible spectrophotometric, Fourier-transform infrared, electron dispersive X-ray spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses confirmed synthesis of AgNPs. TEM micrographs revealed presence of well-dispersed AgNPs predominantly of small size and different shapes with an average particle size of 30.8 nm. Antimicrobial susceptibility tests of AgNP treatments revealed variability in sensitivity of bacteria Bacillus cereus and Saccharophagus degradans under study. Minimum inhibitory concentration (MIC) values of the AgNPs for B. cereus and S. degradans were found to be 30 and 10 μg/mL, respectively. The mixed culture of B. cereus and S. degradans treated with AgNPs at 10 μg/mL showed increase in growth with time, suggesting survival of bacteria in liquid media. The plating of mixed culture before AgNP treatment showed presence of both bacteria, but 24-h-old mixed culture treated with AgNPs at the concentration of 10 μg/mL showed presence of B. cereus colonies. SEM micrographs revealed damage to S. degradans cells but no effect on B. cereus cells after AgNP treatment. Confocal microscopic observations of AgNP-treated mixed cultures by Nile blue A staining indicated intact polyhydroxyalkanoates producing flourescent cells of B. cereus but damage and deformities in S. degradans cells. This study suggests that AgNPs can selectively inhibit growth of S. degradans and retain B. cereus at MIC of S. degradans. This report is a case study for selective inhibition of one bacteria and growth of the other in a culture using plant-synthesized silver nanoparticles.     

Effect of silver nanoparticles on frequency and temperature-dependent electrical parameters of a discotic liquid crystalline material

The effect of silver nanoparticles (AgNPs) of diameters 6 and 100 nm on a discotic liquid crystalline material, namely 2,3,6,7,10,11-hexabutyloxytriphenylene (in short HAT4), has been observed in thermodynamic, electrical and optical texture studies. Silver nanoparticles (0.6 wt%) of diameter ~6 nm demonstrate a negligible (but ~100 nm shows appreciable) effect on the broad temperature range plastic columnar hexagonal (Col_hex) phase (~65.0°C) of pure HAT4. The dielectric studies have been carried out in the frequency range of 10 Hz–35 MHz under homeotropic anchoring conditions of the molecules. In the low frequency region of pure HAT4 and its AgNP composites, a relaxation mode has been observed. AgNPs of 6 nm elevate the value of dielectric permittivity of the plastic columnar hexagonal phase of pure HAT4. The dc conductivity of pure HAT4 and its AgNP composite (6 and 100 nm) material has been determined. The optical band gap for pure and AgNP composites of HAT4 has been determined by the ultraviolet-visible study. Due to insertion of AgNPs, the optical band gap of HAT4 has reduced.     

Ultraviolet nanosecond laser ablation behavior of silver nanoparticle and melamine–formaldehyde resin-coated short sisal fiber-modified PLA composites

Nd:YAG laser (355 nm) induced surface modifications in polylactic acid (PLA), and its composites with silver nanoparticles (AgNPs, size range between 120 and 150 nm) with and without additional melamine–formaldehyde-coated short sisal fibers were studied as a function of laser pulse numbers. The AgNP content was varied (100, 300 and 500 ppm), whereas the sisal content kept as constant (9 mass%). The PLA-based systems with a fully amorphous matrix were irradiated with 1–256 laser pulses at a constant fluence of 0.32 µJ µm^?2. Changes in the irradiated surfaces were assessed and quantified by light and scanning electron microscopic pictures. Protrusion with bubbling, bubbled protrusion with cratering and crater formation with more or less bubbled ridges were found as characteristic ablation features. Bubbling was traced to entrapped gaseous products of PLA degradation, while the onset of ridges was ascribed to the melt flow of the PLA matrix caused by laser shock waves. The laser irradiation caused damage and ablation highly depended on the actual composition, which influenced the UV absorption at 355 nm, which was measured as well.     

Differentiation and characterization of isotopically modified silver nanoparticles in aqueous media using asymmetric-flow field flow fractionation coupled to optical detection and mass spectrometry

The principal objective of this work was to develop and demonstrate a new methodology for silver nanoparticle (AgNP) detection and characterization based on asymmetric-flow field flow fractionation (A4F) coupled on-line to multiple detectors and using stable isotopes of Ag. This analytical approach opens the door to address many relevant scientific challenges concerning the transport and fate of nanomaterials in natural systems. We show that A4F must be optimized in order to effectively fractionate AgNPs and larger colloidal Ag particles. With the optimized method one can accurately determine the size, stability and optical properties of AgNPs and their agglomerates under variable conditions. In this investigation, we couple A4F to optical absorbance (UV–vis spectrometer) and scattering detectors (static and dynamic) and to an inductively coupled plasma mass spectrometer. With this combination of detection modes it is possible to determine the mass isotopic signature of AgNPs as a function of their size and optical properties, providing specificity necessary for tracing and differentiating labeled AgNPs from their naturally occurring or anthropogenic analogs. The methodology was then applied to standard estuarine sediment by doping the suspension with a known quantity of isotopically enriched ¹⁰⁹AgNPs stabilized by natural organic matter (standard humic and fulvic acids). The mass signature of the isotopically enriched AgNPs was recorded as a function of the measured particle size. We observed that AgNPs interact with different particulate components of the sediment, and also self-associate to form agglomerates in this model estuarine system. This work should have substantial ramifications for research concerning the environmental and biological fate of AgNPs.     

Biosynthesis of silver nanoparticles using Onosma sericeum Willd. and evaluation of their catalytic properties and antibacterial and cytotoxic activity

In this study, silver nanoparticle (AgNP) synthesis was carried out using Onosma sericeum Willd. aqueous extract for the first time, with a simple, economical, and green method without the need for any other organic solvent or external reducing or stabilizing agent. A variety of AgNPs, all of different particle sizes, were synthesized by controlling the silver ion concentration, extract volume, temperature, and pH. It was determined that the optimum conditions for AgNP synthesis were 1 mM AgNO3, pH 8, 25 °C, 20 g/200 mL extract, silver nitrate, and extract ratio 5:1 (v/v). The AgNPs were defined using UV-Vis spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The particle size distribution and zeta potential measurements of the AgNPs were measured using the dynamic light scattering (DLS) technique. It was determined that the AgNPs with a particle size of less than 10 nm showed a higher catalytic effect in the reduction of 2-nitrobenzenamine. It was also found that these nanoparticles had a cytotoxic effect on the MCF-7 breast cancer cell line depending on dosage and time. The resulting IC50 values were between 76.63 µg/mL and 169.77 µg/mL. Furthermore, the biosynthesized AgNPs showed effective antibacterial activity against the Acinetobacter baumannii bacteria. The results of the study showed that synthesized AgNPs can have a promising role in biomedical and nanobiotechnology applications.     

The potential of asymmetric flow field-flow fractionation hyphenated to multiple detectors for the quantification and size estimation of silica nanoparticles in a food matrix

This work represents a first systematic approach to the size-based elemental quantification and size estimation of metal(loid) oxide nanoparticles such as silica (SiO₂) in a real food matrix using asymmetric flow field-flow fractionation coupled online with inductively coupled plasma mass spectrometry (ICP-MS) and multi-angle light scattering (MALS) and offline with transmission electron microscopy (TEM) with energy-dispersive X-ray analysis (EDAX). Coffee creamer was selected as the model sample since it is known to contain silica as well as metal oxides such as titania at the milligramme per kilogramme levels. Optimisation of sample preparation conditions such as matrix-to-solvent ratio, defatting with organic solvents and sonication time that may affect nanoparticle size and size distribution in suspensions was investigated. Special attention was paid to the selection of conditions that minimise particle transformation during sample preparation and analysis. The coffee creamer matrix components were found to stabilise food grade SiO₂ particles in comparison with water suspensions whilst no significant effect of defatting using hexane was found. The use of sample preparation procedures that mimic food cooking in real life was also investigated regarding their effect on particle size and particle size distribution of silica nanoparticles in the investigated food matrix; no significant effect of the water temperature ranging from ambient temperature to 60 °C was observed. Field-flow fractionation coupled to inductively coupled plasma-mass spectrometry (FFF-ICP-MS) analysis of extracts of both unspiked coffee creamer and coffee creamer spiked with food grade silicon dioxide, using different approaches for size estimation, enabled determination of SiO₂ size-based speciation. Element-specific detection by ICP-MS and post-FFF calibration with elemental calibration standards was used to determine the elemental composition of size fractions separated online by FFF. Quantitative data on mass balance is provided for the size-based speciation of the investigated inorganic nano-objects in the complex matrix. The combination of FFF with offline fractionation by filtration and with detection by ICP-MS and TEM/EDAX has been proven essential to provide reliable information of nanoparticle size in the complex food matrix.

Interactions and stability of silver nanoparticles in the aqueous phase: Influence of natural organic matter (NOM) and ionic strength

The rapid development of nanotechnology and the related production and application of nanosized materials such as engineered nanoparticles (ENP) inevitably lead to the emission of these products into environmental systems. So far, little is known about the occurrence and the behaviour of ENP in environmental aquatic systems. In this contribution, the influence of natural organic matter (NOM) and ionic strength on the stability and the interactions of silver nanoparticles (n-Ag) in aqueous suspensions was investigated using UV–vis spectroscopy and asymmetrical flow field-flow fractionation (AF⁴) coupled with UV–vis detection and mass spectrometry (ICP-MS). n-Ag particles were synthesized by chemical reduction of AgNO₃ with NaBH₄ in the liquid phase at different NOM concentrations. It could be observed that the destabilization effect of increasing ionic strength on n-Ag suspensions was significantly decreased in the presence of NOM, leading to a more stable n-Ag particle suspension. The results indicate that this behaviour is due to the adsorption of NOM molecules onto the surface of n-Ag particles (“coating”) and the resulting steric stabilization of the particle suspension. The application of AF⁴ coupled with highly sensitive detectors turned out to be a powerful method to follow the aggregation of n-Ag particle suspensions at different physical–chemical conditions and to get meaningful information on their chemical composition and particle size distributions. The method described will also open the door to obtain reliable data on the occurrence and the behaviour of other ENP in environmental aquatic systems.     

Pongamia pinnata seed extract‐mediated green synthesis of silver nanoparticles: Preparation,formulation and evaluation of bactericidal and wound healing potential

Pongamia pinnata – a plant used since olden times in Ayurvedic treatment – is reported to have diverse functions including antibacterial, antidiabetic, antineurodegenerative, antiepileptic, antiulcer, etc. In this study, our objective was to prepare silver nanoparticles (AgNPs) by green synthesis mediated by methanolic seed extract of P. pinnata and to determine their antimicrobial and antioxidant potential and wound healing activity. AgNPs were characterized for particle size and shape and for antioxidant potential. Further, the AgNPs were incorporated in a gel. The wound healing activity was investigated using an excision wound healing model in Wistar rats. The AgNP‐loaded gel was applied topically to the wounded rats daily for 30 days. The wound contraction was calculated and histopathological studies of the healed tissues were conducted. Karanjin content of the extract was found to be 349 ± 2.16 mg g^?1. Formation of AgNPs was confirmed using transmission and scanning electron microscopies and X‐ray diffraction. AgNPs showed good antioxidant potential and were active against Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa. Significant wound healing activity (p < 0.05) was shown by the AgNP gel as compared to 5% Betadine ointment. Thus, the prepared AgNPs have antimicrobial and wound healing effects that may be useful in treatment of topical infections especially in wounds.     

Sensitive determination of the endocrine disruptor bisphenol A at ultrathin film based on nanostructured hybrid material SiO<Subscript>2</Subscript>/GO/AgNP

In this work, we described an electrochemical sensor using a nanocomposite based on graphene oxide (GO), silver nanoparticles (AgNP), and disordered mesoporous silica (SiO₂), which was used for the determination of bisphenol A in water samples. Initially, the hybrid material SiO₂/GO was synthesized via sol-gel process, subsequently decorated with AgNP with an approximate 20 nm particle size prepared directly on the surface of the SiO₂/GO using N, N-dimethylformamide (DMF) as an agent reducer. A glassy carbon electrode was modified with SiO₂/GO/AgNP and used in developing a sensitive electrochemical sensor for the determination of bisphenol A in phosphate buffer 0.1 mol L^?1 (pH 7.0). The detection limit was 45.2 nmol L^?1 with a linear response range between 1.0 × 10^?7 and 2.6 × 10^?6 mol L^?1 and a sensitivity of 1.27 × 10^?7 A mol^?1 L. Finally, the optimized electrochemical sensor was used for the quantitation of endocrine interfering in natural waters.     

Detection of silver nanoparticles in parsley by solid sampling high-resolution–continuum source atomic absorption spectrometry

In this work, we present a fast and simple approach for detection of silver nanoparticles (AgNPs) in biological material (parsley) by solid sampling high-resolution–continuum source atomic absorption spectrometry (HR-CS AAS). A novel evaluation strategy was developed in order to distinguish AgNPs from ionic silver and for sizing of AgNPs. For this purpose, atomisation delay was introduced as significant indication of AgNPs, whereas atomisation rates allow distinction of 20-, 60-, and 80-nm AgNPs. Atomisation delays were found to be higher for samples containing silver ions than for samples containing silver nanoparticles. A maximum difference in atomisation delay normalised by the sample weight of 6.27?±?0.96 s mg^?1 was obtained after optimisation of the furnace program of the AAS. For this purpose, a multivariate experimental design was used varying atomisation temperature, atomisation heating rate and pyrolysis temperature. Atomisation rates were calculated as the slope of the first inflection point of the absorbance signals and correlated with the size of the AgNPs in the biological sample. Hence, solid sampling HR-CS AAS was proved to be a promising tool for identifying and distinguishing silver nanoparticles from ionic silver directly in solid biological samples.

Antibacterial effect of silver nanoparticles prepared in bipolymers at moderate temperature

The purpose of this study was to investigate the antibacterial effect of silver nanoparticles in chitosan–poly(ethylene glycol) suspension. The silver nanoparticles (AgNPs) were prepared by use of an environmentally benign method from chitosan (Cts) and poly(ethylene glycol) (PEG) at moderate temperature and with stirring for different times. Silver nitrate (AgNO₃) was used as the metal precursor and Cts and PEG were used as solid support and polymeric stabilizer, respectively. The antibacterial activity of silver–chitosan–poly(ethylene glycol) nanocomposites (Ag–Cts–PEG NCs) against Staphylococcus aureus, Micrococcus luteum, Pseudomonas aeruginosa, and Escherichia coli was tested by use of the Mueller–Hinton agar disk-diffusion method. Formation of AgNPs was determined by UV–visible spectroscopy; surface plasmon absorption maxima were observed at 415–430 nm in the UV–visible spectrum. The peaks in the XRD pattern confirmed that the AgNPs had a face-centered cubic structure; peaks of contaminated crystalline phases were not observed. Transmission electron microscopy (TEM) revealed that the AgNPs synthesized were spherical. The optimum stirring time for synthesis of the smallest particle size (mean diameter 5.50 nm) was 12 h. The AgNPs in Cts–PEG were effective against all the bacteria tested. Higher antibacterial activity was observed for AgNPs with smaller size. These results suggest that AgNPs can be used as an effective inhibitor of bacteria and can be used in medical applications. These results also suggest that AgNPs were successfully synthesized in Cts–PEG suspension at moderate temperature with different stirring times.     

Biological Evaluation of Silver Nanoparticles Obtained from T. arjuna Bark Extract as Both Reducing and Capping Agent

A simple, environmentally benign and cost effective method is reported to obtain silver nanoparticles (AgNPs) using aqueous solution of AgNO₃ and T. Arjuna (Terminalia Arjuna) bark extract, which act as both reducing and capping agent, under microwave irradiation. The formation of AgNPs was monitored by recording optical absorption spectra for surface plasmon resonance observed at ~425 nm. The bioactive polyphenols extracted from the plant extract are responsible for reduction of Ag⁺ → Ag⁰. During the formation of AgNPs, the reaction mixture showed gradual decrease in pH and an increase in reduction potential. The powder XRD pattern of AgNPs confirmed their fcc structure. An FTIR spectrum showed the presence of plant-residues adsorbed on the surface of AgNPs, which indicates the in situ bio-capping. The TG curve of AgNPs showed ~30 % weight loss due to thermal degradation of these plant-residues. The FE-SEM images showed spherical shape of AgNPs with an average particle size of 10–15 nm. The EDX analysis confirmed the presence of Ag as a major element. The biological evaluation of AgNPs showed higher inhibitory action for both bacteria and yeast when compared to that of fungus. A very good antioxidant property was also observed for these bio-capped AgNPs.     

Ficus carica Latex-Mediated Synthesis of Silver Nanoparticles and Its Application as a Chemophotoprotective Agent

The present work provides scientific support on the use of latex of Ficus carica to synthesize stable silver nanoparticles (AgNPs). AgNPs synthesized immediately after the addition of latex to silver nitrate solution at room temperature. Synthesized nanoparticles were of spherical shape with average size of 163.7 nm. Fourier transform infrared spectroscopy analysis revealed capping of proteins and phenolic compound on AgNPs, while X-ray diffraction analysis confirmed the fcc nature of AgNPs. Particles formed were stable for a long time (6 months). It was found that incorporation of AgNPs with 2 and 4 % concentration exhibits synergistic increase in sun protection factor of commercial sunscreen and natural extracts ranging from 01 to 12,175 % than control. Further characterization of latex and AgNPs revealed total phenolic content of 98.75 and 94.88 μg/ml. The ferric ion reduction potentials of latex and AgNPs were 79.69 and 18.79 %. Reduction potential of ascorbic acid was synergistically increased after cumulative preparation of ascorbic acid with latex and AgNPs and found to be 106.76 and 101.50 % for ascorbic acid + latex and ascorbic acid + AgNPs, respectively.     

Clay-mediated synthesis of silver nanoparticles exhibiting low-temperature melting

Nanohybrids of silver nanoparticles (AgNPs) supported on mica clay were synthesized by in situ reduction of silver nitrate in an aqueous solution. The required mica platelets of high aspect ratio were previously prepared by the exfoliation of mica clay stacks in a multilayered structure through an ionic exchange reaction with poly(oxypropylene)-amine-salt. The exfoliated nanoscale mica platelets (Mica) are polydispersed such that each platelet is 300-1000 nm in width and 1 nm in thickness. These platelets possess ionic charges in the form of ≡SiO(-)Na(+) at 120 mequiv/100 g and are suitable for supporting AgNPs in the process of in situ reduction of silver nitrate. Transmission electronic microscopy revealed the formation of AgNPs with a narrow size distribution of ca. 8 nm in diameter on the rim of individual Mica platelets. However, the pristine layered Mica structure without exfoliation failed to produce a fine AgNP distribution but instead generated particles larger than 30 nm and some precipitates. Characterization by differential scanning calorimetry and field emission scanning electron microscopy revealed that the fine AgNPs on Mica platelets exhibited a low melting temperature of 110 °C. The AgNP/Mica nanohybrid not containing an organic dispersant is considered to be a "naked" silver particle.     

Characterization of silver nanoparticles using flow-field flow fractionation interfaced to inductively coupled plasma mass spectrometry

The ability to detect and identify the physiochemical form of contaminants in the environment is important for degradation, fate and transport, and toxicity studies. This is particularly true of nanomaterials that exist as discrete particles rather than dissolved or sorbed contaminant molecules in the environment. Nanoparticles will tend to agglomerate or dissolve, based on solution chemistry, which will drastically affect their environmental properties. The current study investigates the use of field flow fractionation (FFF) interfaced to inductively coupled plasma-mass spectrometry (ICP-MS) as a sensitive and selective method for detection and characterization of silver nanoparticles. Transmission electron microscopy (TEM) is used to verify the morphology and primary particle size and size distribution of precisely engineered silver nanoparticles. Subsequently, the hydrodynamic size measurements by FFF are compared to dynamic light scattering (DLS) to verify the accuracy of the size determination. Additionally, the sensitivity of the ICP-MS detector is demonstrated by fractionation of μg/L concentrations of mixed silver nanoparticle standards. The technique has been applied to nanoparticle suspensions prior to use in toxicity studies, and post-exposure biological tissue analysis. Silver nanoparticles extracted from tissues of the sediment-dwelling, freshwater oligochaete Lumbriculus variegatus increased in size from approximately 31-46nm, indicating a significant change in the nanoparticle characteristics during exposure.