Size and isotope analysis of individual nanoparticles by multi-collector ICP-MS using "event-triggered signal capture" with a high-speed oscilloscope.

Accurate quantitative elemental and isotope analysis of nanoparticles at the single-particle level is crucial for better understanding their origin, properties and behaviors. Single particle inductively coupled plasma-mass spectrometry (spICP-MS) has emerged as a promising technique for nanoparticle analysis. However, challenges persist in obtaining accurate and consistent element profiles and ratios for small-sized nanoparticles by conventional quadrupole (QMS) or time-of-flight mass analyzers (TOF-MS) due to their low level and transient nature. In this paper, we present a novel analytical method for single nanoparticle analysis using multiple collector ICP-MS (MC-ICP-MS) combined with a modern high-speed digital oscilloscope. The single particle events are acquired using an "event-triggered signal capture" (ETSC) technique, which enables the simultaneously capture and visualization of multiple isotopes of transient individual particle profiles with nanosecond time resolution. This greatly facilitates precise and efficient analysis of nanoparticles. The minimum detectable particle size is calculated to be as small as 8 nm (∼1 ag 109Ag) for AgNPs. Based on the 109/107Ag ratios obtained from 2000 particles, the precisions of 109/107Ag ratio measurements on 20 nm, 40 nm, 60 nm, 80 nm and 100 nm were approximately 0.086 (SD), 0.063 (SD), 0.051 (SD), 0.040 (SD), and 0.029 (SD), which is limited by counting statistics of the isotopic signals. Furthermore, the achieved standard error of 109/107Ag can be reduced to sub-permil level (0.7 ‰) even for the measurement of 20 nm AgNPs (N = 17,000). These results demonstrate that the ETSC provides a unique method for isotope analysis of single particles, holding great potential for enhancing our understanding of nanoparticles.

An Unprecedented Metal Distribution in Silica Nanoparticles Determined by Single-Particle Inductively Coupled Plasma Mass Spectrometry.

Metal-containing nanoparticles are now common in applications ranging from catalysts to biomarkers. However, little research has focused on per-particle metal content in multicomponent nanoparticles. In this work, we used single-particle inductively coupled plasma mass spectrometry (ICP-MS) to determine the per-particle metal content of silica nanoparticles doped with tris(2,2'-bipyridyl)ruthenium(II). Monodispersed silica nanoparticles with varied Ru doping levels were prepared using a water-in-oil microemulsion method. These nanoparticles were characterized using common bulk-sample methods such as absorbance spectroscopy and conventional ICP-MS, and also with single-particle ICP-MS. The results showed that averaged concentrations of metal dopant measured per-particle by single-particle ICP-MS were consistent with the bulk-sample methods over a wide range of dopant levels. However, the per-particle amount of metal varied greatly and did not adhere to the usual Gaussian distribution encountered with one-component nanoparticles, such as gold or silver. Instead, the amount of metal dopant per silica particle showed an unexpected geometric distribution regardless of the prepared doping levels. The results indicate that an unusual metal dispersal mechanism is taking place during the microemulsion synthesis, and they challenge a common assumption that doped silica nanoparticles have the same metal content as the average measured by bulk-sample methods.

Ti-containing NPs in raw water and their removal with conventional treatments in four water treatment plants in Taiwan.

The ingestion of Ti-containing nanoparticles from drinking water has emerged as a concern in recent years. This study therefore aimed to characterize Ti-containing nanoparticles in water samples collected from four water treatment plants in Taiwan and to explore the challenges associated with measuring them at low levels using single particle-inductively coupled plasma mass spectrometry. Additionally, the study sought to identify the most effective processes for the removal of Ti-containing nanoparticles. For each water treatment plant, two water samples were collected from raw water, sedimentation effluent, filtration effluent, and finished water, respectively. Results revealed that Ti-containing nanoparticles in raw water, with levels at 8.69 µg/L and 296.8 × 103 particles/L, were removed by approximately 35% and 98%, respectively, in terms of mass concentration and particle number concentration, primarily through flocculation and sedimentation processes. The largest most frequent nanoparticle size in raw water (112.0 ± 2.8 nm) was effectively reduced to 62.0 ± 0.7 nm in finished water, while nanoparticles in the size range of 50-70 nm showed limited changes. Anthracite was identified as a necessary component in the filter beds to further improve removal efficiency at the filtration unit. Moreover, the most frequent sizes of Ti-containing nanoparticles were found to be influenced by salinity. Insights into the challenges associated with measuring low-level Ti-containing nanoparticles in aqueous samples provide valuable information for future research and management of water treatment processes, thereby safeguarding human health.

Characterization of nanoparticles in silicon dioxide food additive.

Silicon dioxide (SiO2), in its amorphous form, is an approved direct food additive in the United States and has been used as an anticaking agent in powdered food products and as a stabilizer in the production of beer. While SiO2 has been used in food for many years, there is limited information regarding its particle size and size distribution. In recent years, the use of SiO2 food additive has raised attention because of the possible presence of nanoparticles. Characterization of SiO2 food additive and understanding their physicochemical properties utilizing modern analytical tools are important in the safety evaluation of this additive. Herein, we present analytical techniques to characterize some SiO2 food additives, which were obtained directly from manufacturers and distributors. Characterization of these additives was performed using dynamic light scattering (DLS), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and single-particle inductively coupled plasma mass spectrometry (spICP-MS) after the food additive materials underwent different experimental conditions. The data obtained from DLS, spICP-MS, and electron microscopy confirmed the presence of nanosized (1-100 nm) primary particles, as well as aggregates and agglomerates of aggregates with sizes greater than 100 nm. SEM images demonstrated that most of the SiO2 food additives procured from different distributors showed similar morphology. The results provide a foundation for evaluating the nanomaterial content of regulated food additives and will help the FDA address current knowledge gaps in analyzing nanosized particles in commercial food additives.

Critical evaluation of key parameters in single particle ICP-MS data processing for the correct determination of platinum nanoparticles in complex environmental and biological matrices.

There is an urgent need for the harmonization of critical parameters in single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) and they have been deeply studied and optimized in the present work using platinum nanoparticles (PtNPs) as a representative case of study. Special attention has been paid to data processing in order to achieve an adequate discrimination between signals. Thus, a comparison between four different algorithms has been performed and the method for transport efficiency calculation has also been thorougly evaluated (finding the use of a well-characterized solution of the same targeted analyte (30 nm PtNPs) as adequate). The best results have been obtained after the application of a deconvolution approach for the data processing and using 5 ms as dwell time and 40,000 data points for data acquisition. Under the optimized conditions, a correct discrimination between NP events and background signal up to 100 or 750 ng L-1 of added ionic Pt was reached for 30 and 50 nm PtNPs, respectively. The suitability of the developed method for the characterization of PtNPs in relevant environmental (water samples) and biological (cell culture media) matrices has also been demonstrated.

Silver ion-imprinted magnetic adsorbent hyphenated to single particle-ICP-MS for separation and analysis of dissolved silver and silver nanoparticles in antibacterial gel extracts.

BACKGROUND: Silver nanoparticles (Ag NPs) are extensively used in various applications, but their reactivity leads to oxidative dissolution into Ag(I). When dealing with real samples involving Ag NPs, it is inevitable to encounter situations where both Ag NPs and Ag(I) coexist. Single particle-inductively coupled plasma mass spectrometry (SP-ICP-MS) is a valuable technique for nanoparticle size characterization. However, the presence of coexisting dissolved ions strongly interferes with the accuracy of particle size analysis using SP-ICP-MS. Therefore, it is crucial to develop a reliable separation analysis method to accurately measure both Ag NPs and Ag(I). RESULTS: In this study, we synthesized a silver ion-imprinted magnetic adsorbent with high adsorption capacity (149 mg g-1) and rapid adsorption kinetics (30 min) at both µg L-1 and mg L-1 concentration. The adsorbent selectively adsorbs Ag(I) at pH 7 while hardly adsorbing Ag NPs. It is reusable for more than 5 cycles after regeneration. Using this magnetic adsorbent prior to SP-ICP-MS, we accurately determined the sizes of standard Ag NPs in agreement with the size determined by transmission electron microscopy. The detection limit of particle size and number concentrations of Ag NPs was 12.6 nm and 6.3 × 105 particles L-1. Moreover, we successfully applied the developed method to analyze Ag(I) and Ag NPs in antibacterial gel extracts and validated its accuracy through acid digestion-ICP-MS, TEM, and spiking experiments. SIGNIFICANCE AND NOVELTY: Direct SP-ICP-MS analysis in the presence of Ag(I) led to a high baseline, obscuring signals from smaller Ag NPs. Our method of selectively removing Ag(I) substantially improves the accuracy of Ag NPs detection via SP-ICP-MS in the antibacterial gel extracts (e.g. from 48.26 to 35.67 nm). Compared to other approaches used in SP-ICP-MS, our method has a higher adsorption capacity, allowing for better tolerance of coexisting Ag(I).

Exploring Pt-Pd Alloy Nanoparticle Cluster Formation through Conventional Sizing Techniques and Single-Particle Inductively Coupled Plasma-Sector Field Mass Spectrometry.

Accurate characterization of Pt-Pd alloy nanoparticle clusters (NCs) is crucial for understanding their synthesis using Gas-Diffusion Electrocrystallization (GDEx). In this study, we propose a comprehensive approach that integrates conventional sizing techniques-scanning electron microscopy (SEM) and dynamic light scattering (DLS)-with innovative single-particle inductively coupled plasma-sector field mass spectrometry (spICP-SFMS) to investigate Pt-Pd alloy NC formation. SEM and DLS provide insights into morphology and hydrodynamic sizes, while spICP-SFMS elucidates the particle size and distribution of Pt-Pd alloy NCs, offering rapid and orthogonal characterization. The spICP-SFMS approach presented enables detailed characterization of Pt-Pd alloy NCs, which was previously challenging due to the absence of multi-element capabilities in conventional spICP-MS systems. This innovative approach not only enhances our understanding of bimetallic nanoparticle synthesis, but also paves the way for tailoring these materials for specific applications, marking a significant advancement in the field of nanomaterial science.

Bioaccumulation of titanium dioxide nanoparticles in green (Ulva sp.) and red (Palmaria palmata) seaweed.

A bioaccumulation study in red (Palmaria palmata) and green (Ulva sp.) seaweed has been carried out after exposure to different concentrations of citrate-coated titanium dioxide nanoparticles (5 and 25 nm) for 28 days. The concentration of total titanium and the number and size of accumulated nanoparticles in the seaweeds has been determined throughout the study by inductively coupled plasma mass spectrometry (ICP-MS) and single particle-ICP-MS (SP-ICP-MS), respectively. Ammonia was used as a reaction gas to minimize the effect of the interferences in the 48Ti determination by ICP-MS. Titanium concentrations measured in Ulva sp. were higher than those found in Palmaria palmata for the same exposure conditions. The maximum concentration of titanium (61.96 ± 15.49 µg g-1) was found in Ulva sp. after 28 days of exposure to 1.0 mg L-1 of 5 nm TiO2NPs. The concentration and sizes of TiO2NPs determined by SP-ICP-MS in alkaline seaweed extracts were similar for both seaweeds exposed to 5 and 25 nm TiO2NPs, which indicates that probably the element is accumulated in Ulva sp. mainly as ionic titanium or nanoparticles smaller than the limit of detection in size (27 nm). The implementation of TiO2NPs in Ulva sp. was confirmed by electron microscopy (TEM/STEM) in combination with energy dispersive X-Ray analysis (EDX).

Study of the Stability, Uptake and Transformations of Zero Valent Iron Nanoparticles in a Model Plant by Means of an Optimised Single Particle ICP-MS/MS Method.

In the context of the widespread distribution of zero valent iron nanoparticles (nZVI) in the environment and its possible exposure to many aquatic and terrestrial organisms, this study investigates the effects, uptake, bioaccumulation, localisation and possible transformations of nZVI in two different forms (aqueous dispersion-Nanofer 25S and air-stable powder-Nanofer STAR) in a model plant-Arabidopsis thaliana. Seedlings exposed to Nanofer STAR displayed symptoms of toxicity, including chlorosis and reduced growth. At the tissue and cellular level, the exposure to Nanofer STAR induced a strong accumulation of Fe in the root intercellular spaces and in Fe-rich granules in pollen grains. Nanofer STAR did not undergo any transformations during 7 days of incubation, while in Nanofer 25S, three different behaviours were observed: (i) stability, (ii) partial dissolution and (iii) the agglomeration process. The size distributions obtained by SP-ICP-MS/MS demonstrated that regardless of the type of nZVI used, iron was taken up and accumulated in the plant, mainly in the form of intact nanoparticles. The agglomerates created in the growth medium in the case of Nanofer 25S were not taken up by the plant. Taken together, the results indicate that Arabidopsis plants do take up, transport and accumulate nZVI in all parts of the plants, including the seeds, which will provide a better understanding of the behaviour and transformations of nZVI once released into the environment, a critical issue from the point of view of food safety.

Dissolved metal ion removal by online hollow fiber ultrafiltration for enhanced size characterization of metal-containing nanoparticles with single-particle ICP-MS.

Single particle-inductively coupled plasma mass spectrometry (SP-ICP-MS) is a powerful tool for size-characterization of metal-containing nanoparticles (MCNs) at environmentally relevant concentrations, however, coexisting dissolved metal ions greatly interfere with the accuracy of particle size analysis. The purpose of this study is to develop an online technique that couples hollow fiber ultrafiltration (HFUF) with SP-ICP-MS to improve the accuracy and size detection limit of MCNs by removing metal ions from suspensions of MCNs. Through systematic optimization of conditions including the type and concentration of surfactant and complexing agent, carrier pH, and ion cleaning time, HFUF completely removes metal ions but retains the MCNs in suspension. The optimal conditions include using a mixture of 0.05 vol.% FL-70 and 0.5 mmol/L Na2S2O3 (pH = 8.0) as the carrier and 4 min as the ion cleaning time. At these conditions, HFUF-SP-ICP-MS accurately determines the sizes of MCNs, and the results agree with the size distribution determined by transmission electron microscopy, even when metal ions also are present in the sample. In addition, reducing the ionic background through HFUF also lowers the particle size detection limit with SP-ICP-MS (e.g., from 28.3 to 14.2 nm for gold nanoparticles). This size-based ion-removal principle provided by HFUF is suitable for both cations (e.g., Ag+) and anions (e.g., AuCl4-) and thus has good versatility compared to ion exchange purification and promising prospects for the removal of salts and macromolecules before single particle analysis.

A Single-Step Digestion for the Quantification and Characterization of Trace Particulate Silica Content in Biological Matrices Using Single Particle Inductively Coupled Plasma-Mass Spectrometry.

The increased use of amorphous silica nanoparticles (SiNPs) in food products, materials science, cosmetics, and pharmaceuticals has raised questions about potential hazards in the environment and in human health. Although SiNPs are generally thought to be benign, recent studies have demonstrated toxicity in different cell and animal models. Despite their ubiquitous use, SiNPs are rarely analyzed quantitatively. Often, the methods used to analyze silicon and SiNPs are difficult, costly, require the use of dangerous reagents, and are prone to interferences. Additionally, characterization of SiNPs in complex matrices requires extensive sample preparation. To address this, we propose a single-step digestion method for the determination of trace SiNP content in biological matrices. For conventional inductively coupled plasma-mass spectrometry (ICP-MS) analysis, biological samples are often digested with concentrated HNO3. We found that with conventional ICP-MS, lower limits of detection (LLOD) of silicon are too high for trace analysis. However, we found that SiNPs are stable at a strong acidic pH; thus, concentrated HNO3 could be used to digest biological samples leaving SiNPs intact. Then, by analysis with single particle ICP-MS, we found that the smallest SiNP that could be read was 185 nm in size. The concentration for the LLOD was found to be 0.032 ppb with interday variability in sizing and concentration at 2.5% and 6.8% respectively. Utilizing this method, SiNPs were accurately sized and counted in cell pellets and media. Our proposed method can be used to accurately quantify and characterize SiNPs (or agglomerated SiNPs) larger than the derived LLOD in a variety of biological matrices and will assist in determining relationships between exposures of SiNPs and toxicity in humans and the environment.

Ultrasensitive detection of multiple cancer biomarkers by a triple cascade amplification strategy in combination with single particle inductively coupled plasma mass spectrometry.

A versatile triple cascade amplification strategy was developed for ultrasensitive simultaneous detection of multiple cancer biomarkers using single particle inductively coupled plasma mass spectrometry (spICP-MS). The triple cascade amplification strategy consisted of an enhanced RecJf exonuclease-assisted target recycling amplification module, a hybridization chain reaction amplification module, and a signal amplification module based on DNA-templated multiple metal nanoclusters. In the enhanced RecJf exonuclease-assisted target recycling amplification module, the DNA bases at the 5' ends of aptamers for specific recognition of biomarkers were deliberately replaced by the corresponding RNA bases to enhance amplification efficiency. The signal amplification module based on DNA-templated multiple metal nanoclusters was innovatively used to amplify the signals measured by spICP-MS and at the same time effectively suppress possible background interferences. The proposed spICP-MS platform achieved satisfactory quantitative results for both carcinoembryonic antigen (CEA) and a-fetoprotein (AFP) in human serum samples with accuracy comparable to that of the commercial ELISA kits. Moreover, it has wide dynamic ranges for both CEA (0.01-100 ng/mL) and AFP (0.01-200 ng/mL). The limit of detection for CEA and AFP was 0.6 and 0.5 pg/mL, respectively. Compared with conventional biomarkers detection methods, the proposed spICP-MS platform has the advantages of operational simplicity, ultra-high sensitivity, wide dynamic range, and low background. Therefore, it is reasonable to expect that the proposed spICP-MS platform can be further developed to be a promising alternative tool for biomarker detection in fields of clinical diagnosis and biomedical research.

Silver Nanoparticles and Ionic Silver Separation Using a Cation-Exchange Resin. Variables Affecting Their Separation and Improvements of AgNP Characterization by SP-ICPMS.

Silver nanoparticles (AgNPs) are frequently found in everyday products and, as a consequence, their release into the environment cannot be avoided. Once in aquatic systems, AgNPs interact with natural constituents and undergo different transformation processes. Therefore, it is important to characterize and quantify AgNPs in environmental waters in order to understand their behavior, their transformation, and their associated toxicological risks. However, the coexistence of ionic silver (Ag+) with AgNPs in aquatic systems is one of the greatest challenges for the determination of nanosilver. Ion-exchange resins can be used to separate Ag+ from AgNPs, taking advantage of the different charges of the species. In this work, Dowex 50W-X8 was used to separate Ag+ and AgNPs in order to easily determine AgNP concentrations using inductively coupled plasma optical emission spectroscopy. The separation methodology was successfully applied to river water samples with different ratios of Ag+ and AgNPs. However, the methodology is not useful for wastewater samples. The described methodology also demonstrated an improvement in the determination of the particle size of AgNPs present in river waters by single particle inductively coupled plasma mass spectrometry when a significant amount of Ag+ is also present.

Characterization of Gold Nanorods Conjugated with Synthetic Glycopolymers Using an Analytical Approach Based on spICP-SFMS and EAF4-MALS.

A new comprehensive analytical approach based on single-particle inductively coupled plasma-sector field mass spectrometry (spICP-SFMS) and electrical asymmetric-flow field-flow-fractionation combined with multi-angle light scattering detection (EAF4-MALS) has been examined for the characterization of galactosamine-terminated poly(N-hydroxyethyl acrylamide)-coated gold nanorods (GNRs) in two different degrees of polymerization (DP) by tuning the feed ratio (short: DP 35; long: DP 60). spICP-SFMS provided information on the particle number concentration, size and size distribution of the GNRs, and was found to be useful as an orthogonal method for fast characterization of GNRs. Glycoconjugated GNRs were separated and characterized via EAF4-MALS in terms of their size and charge and compared to the bare GNRs. In contrast to spICP-SFMS, EAF4-MALS was also able of providing an estimate of the thickness of the glycopolymer coating on the GNRs surface.

[Application of non-stationary phase separation hyphenated with inductively coupled plasma mass spectrometry in the analysis of trace metal-containing nanoparticles in the environment].

Engineered metal-containing nanoparticles (MCNs), which have unique physical and chemical properties, are widely used in various fields such as medicine, pharmaceuticals, and microelectronics as well as in daily supplies. These MCNs are inevitably released into the environment during production and use, thus posing a threat to bacterial communities, animals, plants, and human health. There are also abundant natural MCNs in the environment, which play an important role in the environmental cycle of metals. The shape, size, and surface properties of MCNs have a significant impact on their migration, chemical and physical transformation, and biological intake in the environment. Therefore, the analysis and detection of MCNs in the environment should be aimed not only at quantifying their concentration and chemical composition, but also at determining their shape, particle size, and surface charge. In addition, for the detection of MCNs in the environment, challenges due to their low concentrations and the interference from complex environmental matrices must be overcome. A single detection technique is often insufficient for the analysis and detection of MCNs in a complex environment matrix. Therefore, the development of an effective and reliable online hyphenated technique is urgently needed for the separation and detection of MCNs in the environment. Such online hyphenated techniques should be able to eliminate the interference by complex matrices, improve the particle size detection range, and reduce the element detection limit. The online hyphenation of stationary phase-based separation techniques such as liquid chromatography and gel electrophoresis with inductively coupled plasma-mass spectrometry (ICP-MS) can effectively separate MCNs according to their particle size, with low element detection limits. However, these stationary phase-based separation techniques have a shortcoming of the adsorption of nanoparticles on the stationary phase, which leads to blockage of separation channels and low recoveries of nanoparticles. The online hyphenation of a non-stationary phase separation technique with ICP-MS also shows strong nanoparticle separation ability and low element detection limits, so that the problem of colloid blockage in stationary phase-based separation can be resolved. This method is very promising for the rapid and accurate characterization of the particle size distribution and chemical composition of MCNs. However, it cannot provide information about the nanoparticle number concentration of MCNs and the elemental content of a single MCN. In complex environmental samples, pure MCNs cannot be effectively distinguished from MCNs with environmental corona having different thicknesses or pure MCNs adsorbed on/hetero-agglomerated with inorganic/organic colloids. Online coupling single-particle ICP-MS (SP-ICP-MS), an emerging particle detection technique with non-stationary phase separation, can effectively help overcome the above shortcomings. This method can provide information on the hydrodynamic diameter, metal mass-derived diameter, total number concentration, size-dependent number, and size-dependent mass concentration of MCNs. Therefore, it enables comprehensive characterization of MCNs based on a variety of three-dimensional contour plot chromatograms. This review summarizes the separation mechanisms and applicable detectors for three commonly used non-stationary phase separation techniques: hydrodynamic chromatography (HDC), capillary electrophoresis (CE), and field-flow fractionation (FFF). In addition, it focuses on the characteristics and applications of online-coupling non-stationary phase separation with ICP-MS and SP-ICP-MS. Regarding FFF, this review focuses on the separation techniques that are suitable for online coupling with ICP-MS, such as sedimentation FFF and flow FFF (symmetrical flow FFF, asymmetrical flow FFF, and hollow fiber flow FFF). In addition, the characteristics of the online hyphenation of three non-stationary phase separations, HDC, CE, and flow FFF, with ICP-MS are compared, including the separation mechanism, sample volume, analytical time, detection sensitivity, size range, size resolution, recovery, reproducibility, and capability for ion analysis. Finally, this review proposes the prospects for future development of the online hyphenation of non-stationary phase separation techniques with ICP-MS and SP-ICP-MS.

Combining secondary ion mass spectrometry image depth profiling and single particle inductively coupled plasma mass spectrometry to investigate the uptake and biodistribution of gold nanoparticles in Caenorhabditis elegans.

Analytical techniques capable of determining the spatial distribution and quantity (mass and/or particle number) of engineered nanomaterials in organisms are essential for characterizing nano-bio interactions and for nanomaterial risk assessments. Here, we combine the use of dynamic secondary ion mass spectrometry (dynamic SIMS) and single particle inductively coupled mass spectrometry (spICP-MS) techniques to determine the biodistribution and quantity of gold nanoparticles (AuNPs) ingested by Caenorhabditis elegans. We report the application of SIMS in image depth profiling mode for visualizing, identifying, and characterizing the biodistribution of AuNPs ingested by nematodes in both the lateral and z (depth) dimensions. In parallel, conventional- and sp-ICP-MS quantified the mean number of AuNPs within the nematode, ranging from 2 to 36 NPs depending on the size of AuNP. The complementary data from both SIMS image depth profiling and spICP-MS provides a complete view of the uptake, translocation, and size distribution of ingested NPs within Caenorhabditis elegans.

Detection, size characterization and quantification of silver nanoparticles in consumer products by particle collision coulometry.

Silver nanoparticles (AgNPs) are widely used in industrial and consumer products owing to its antimicrobial nature and multiple applications. Consequently, their release into the environment is becoming a big concern because of their negative impacts on living organisms. In this work, AgNPs were detected at a potential of + 0.70 V vs. Ag/AgCl reference electrode, characterized, and quantified in consumer products by particle collision coulometry (PCC). The electrochemical results were compared with those measured with electron microscopy and single-particle inductively coupled plasma mass spectrometry. The theoretical and practical peculiarities of the application of PCC technique in the characterization of AgNPs were studied. Reproducible size distributions of the AgNPs were measured in a range 10-100 nm diameters. A power allometric function model was found between the frequency of the AgNPs collisions onto the electrode surface and the number concentration of nanoparticles up to a silver concentration of 1010 L-1 (ca. 25 ng L-1 for 10 nm AgNPs). A linear relationship between the number of collisions and the number concentration of silver nanoparticles was observed up to 5 × 107 L-1. The PCC method was applied to the quantification and size determination of the AgNPs in three-silver containing consumer products (a natural antibiotic and two food supplements). The mean of the size distributions (of the order 10-20 nm diameters) agrees with those measured by electron microscopy. The areas of current spikes from the chronoamperogram allow the rapid calculation of size distributions of AgNPs that impact onto the working electrode.

Quantification of titanium dioxide nanoparticles in human urine by single-particle ICP-MS.

The increasing use of titanium dioxide nanoparticles in daily use consumer products such as cosmetics, personal care products, food additives, and even medicine has led to growing concerns regarding human safety. It would be ideal to track exposure to this emerging nanopollutant, for example through bioassays, however, so far nanoparticle assessment in biological matrices such as urine remains challenging. The lack of data is mainly due to the limitations of the current metrology, but also to the low expected concentration in human samples. In this study, a quantification method for titanium dioxide nanoparticles in urine has been developed and validated following the ISO/CEI 17025:2017 guidelines. The detection limit for titanium dioxide nanoparticle mass concentration by single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) was 0.05 ng mL-1. The particle size limit was determined using three different approaches, with the highest calculated limit value approaching 50 nm. Repeatability and reproducibility of 14% and 18% respectively were achieved for particle mass concentration, and 6% for both parameters for particle size determination. Method trueness and recovery were 98% and 84%, respectively.

Characterization of platinum nanoparticles for fuel cell applications by single particle inductively coupled plasma mass spectrometry.

The most effective utilization of platinum (Pt) in fuel cells is achieved through the use of nanoparticles (NPs) that offer a large electrochemically active surface area. Because the stability of NPs decreases as they become smaller, their size and size distribution must be known in order to optimize the catalysts' durability, while offering high catalytic activity. Single particle inductively coupled plasma mass spectrometry (spICPMS) can quantify the mass of metallic NPs suspended in aqueous medium, which can then be converted into a size if the NPs' shape, density and composition are known. In this study, for the first time, spICPMS was compared to transmission electron microscopy (TEM) for the characterization of 10 nm Pt NPs. After verifying the accurate sizing of commercial Pt NPs with diameters of 30, 50 and 70 nm, spICPMS with solution calibration was applied to laboratory-synthesized 10 nm Pt NPs possessing a near spherical shape and 10 ± 2 nm diameter according to TEM. The same NPs were also analyzed by spICPMS with Pt size calibration using Pt NPs standards. Irrespectively of the calibration strategy, spICPMS measured the entire population of 659 Pt NPs (6-65 nm), while TEM analyzed the 500 Pt NPs that appeared isolated in the field of view (6-18 nm). Analysis of the size distribution histograms revealed that the modal and mean diameters were respectively 10 and 11 ± 2 nm using solution calibration, and 12 and 13 ± 2 nm using particle size calibration. Both of these mean diameters are in agreement with the TEM measurements according to a Student's t-test at the 95% confidence level, demonstrating that spICPMS, with a size detection limit of 6 nm, can accurately quantify 10-nm Pt NPs while at the same time analyzing the entire sample.

Development and Evaluation of a System for the Semi-Quantitative Determination of the Physical Properties of Skin After Exposure to Silver Nanoparticles.

In order to ensure the safe usage of silver nanoparticles (nAgs) in cosmetics, it is necessary to reveal the physical properties of nAgs inside the skin, as these properties may change during the process of percutaneous absorption. In this study, we aimed to establish an analytical system based on single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) to determine the physical properties of nAgs in the skin. First, we optimized a pretreatment method for solubilizing the skin samples and then showed that most of the nAgs were recovered by sodium hydroxide treatment while remaining in particle form. For separating the skin into the epidermis and dermis, we screened several conditions of microwave irradiation. The sp-ICP-MS analysis indicated that the application of 200 W for 30 s was optimal, as this condition ensured complete separation of skin layers without changing the physical properties of the majority of nAgs. Finally, we evaluated the in vivo application by analyzing the quantity as well as the physical properties of Ag in the epidermis, dermis, and peripheral blood of mice after exposing the skin to nAgs or Ag+. Subsequent sp-ICP-MS analysis indicated that nAgs could be absorbed and distributed into the deeper layers in the ionized form, whereas Ag+ was absorbed and distributed without a change in physical properties. This study indicates that in order to obtain a comprehensive understanding of the response of skin following exposure to nAgs, it is essential to consider the distribution and particle size of not only nAgs but also Ag+ released from nAgs into the skin.