Gold colloid analysis by inductively coupled plasma-mass spectrometry in a single particle mode

Evaluation of extraction and storage conditions for quantification and characterization of silver nanoparticles in complex samples by single particle-ICP-MS

The extraction of nanoparticles (NPs) from complex matrices and subsequent storage can potentially alter the NPs physicochemical properties and hinder cross-study comparisons. Most NP extraction methods are designed and tested at high nanoparticle concentrations, although (eco)toxicological and regulatory monitoring programs require methods capable of analyzing NPs at environmentally relevant concentrations (lower ppb range). In this study, we investigated how extraction methods affect the characteristics of PVP coated and citrate-stabilized silver NPs (AgNPs) spiked into soil, sewage sludge, and biological samples at environmentally relevant concentrations using Single Particle Inductively Coupled Plasma Mass Spectrometry spICP-MS). Further we investigated the impact of storage temperature (-80°C to 21°C) and storage duration (1-28 days) on the particle characteristics such as particle size. We found that aqueous AgNPs samples with low ionic strength media retained their original characteristics (like particle size, particle concentration and particle-based Ag mass) when preserved at 4°C for up to 28 days. AgNPs dispersed in high ionic strength media were however better preserved at -80°C. Among the extraction agents, tetrasodium pyrophosphate was more efficient in extracting AgNPs from soil and sewage sludge matrices, while Proteinase K was more suitable for biological samples from organisms (earthworms or fish). Although our study focused only on AgNPs, it provides crucial information to aid interlaboratory comparisons and data interpretation for (eco)toxicological studies.

Ion-exchange resins improve the analysis of metal nanoparticles in wastewater using single-particle inductively coupled plasma-mass spectrometry

Improved measurement and analysis technologies are needed for investigating nanoparticle generation characteristics in sewage treatment plants. Single-particle inductively coupled plasma-mass spectrometry (spICP-MS) can be used to analyze metal nanoparticle characteristics. However, during spICP-MS analysis of environmental samples, high concentrations of ionic materials obscure the signals of particulate materials by increasing background signals. This can increase the threshold value for separating background and particle signals and increase the background-equivalent diameter (BED). In this study, particle size distributions in influent and effluent collected from sewage treatment plants were investigated using an improved spICP-MS method combining spICP-MS with ion-exchange resin (IER) column pretreatment. The ion removal effect of the IER column was first examined using a synthetic mixture of Ag nanoparticles (AgNPs) and ions. The method was then applied to wastewater from six different sewage treatment plants using an optimal IER packing of 5 g. The ion removal efficiency for samples containing a proper mixture of AgNPs and Ag ions was 99.98%, and the BED significantly decreased from 73.0 ± 1.0 to 6.1 ± 0.3 nm. Particle size distributions measured in the treatment plant influent and effluent ranged from 28.5 nm (Co) to 220.3 nm (Mg) and from 26.8 nm (Co) to 291.8 nm (Mg), respectively. spICP-MS/IER enabled the detection of smaller particles by removing ions from the sample and significantly decreasing the size detection limit. The results of this study offer a reference for developing predictive models for removing metal nanoparticles during sewage/wastewater treatment.

Past progress in environmental nanoanalysis and a future trajectory for atomic mass-spectrometry methods

The development of engineered nanotechnology has necessitated a commensurate maturation of nanoanalysis capabilities. Building off a legacy established by electron microscopy and light-scattering, environmental nanoanalysis has now benefited from ongoing advancements in instrumentation and data analysis, which enable a deeper understanding of nanomaterial properties, behavior, and impacts. Where once environmental nanoparticles and colloids were grouped into broad 'dissolved or particulate' classes that are dependent on a filter size cut-off, now size distributions of submicron particles can be separated and characterized providing a more comprehensive examination of the nanoscale. Inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS), directly coupled to field flow fractionation (FFF-ICP-QMS) or operated in single particle mode (spICP-MS) have spearheaded a revolution in nanoanalysis, enabling research into nanomaterial behavior in environmental and biological systems at expected release concentrations. However, the complexity of the nanoparticle population drives a need to characterize and quantify the multi-element composition of nanoparticles, which has begun to be realized through the application of time-of-flight MS (spICP-TOFMS). Despite its relative infancy, this technique has begun to make significant strides in more fully characterizing particulate systems and expanding our understanding of nanoparticle behavior. Though there is still more work to be done with regards to improving instrumentation and data processing, it is possible we are on the cusp of a new nanoanalysis revolution, capable of broadening our understanding of the size regime between dissolved and bulk particulate compartments of the environment.

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.

Measuring Size and Number Concentration of Metallic Nanoparticles Using spICP-MS

This protocol describes how to measure the size and concentration of individual metallic nanoparticles using inductively coupled plasma-mass spectrometry (ICP-MS) in single-particle (sp) mode. Accurately determining the size of individual nanoparticles on a per-particle basis, both quickly and accurately, is an ever-increasing need within nanoparticle characterization. ICP-MS is capable of measuring a broad range of metallic nanoparticle sizes with high resolution, thus allowing the measurement of multiple particle populations for the quality assessment of nanoformulations. Additionally, spICP-MS can accurately determine particle concentrations without the need for concentration standards.

Single particle inductively coupled plasma mass spectrometry and its variations for the analysis of nanoparticles

Single particle inductively coupled plasma mass spectrometry (spICPMS) can count and weigh metal-containing nanoparticles (NPs), enabling their sizing if their geometry, density, and composition are known. With a nebulizer and a spray chamber for sample introduction, both the sample uptake rate and the transport efficiency must be determined when calibrating with solutions. In contrast, flow injection (FI) and mono-segmented flow analysis (MSFA) coupled to spICPMS do not need determination of the transport efficiency and sample uptake rate for accurate NP mass measurement. Correcting for the significant settling time on some instruments is also discussed, as well as calibration through signal integration instead of averaging, which eliminates the need to measure the transport efficiency when seeking NP mass. Nitrogen added to the outer plasma gas can reduce the background for the determination of P, S, Ca and Fe. Infrared heating of the sample introduction system provides 100% transport efficiency, enabling accurate particle mass and concentration measurements without measurement of transport efficiency.

Size Uncertainty in Individual Nanoparticles Measured by Single Particle Inductively Coupled Plasma Mass Spectrometry

Single particle inductively coupled plasma mass spectrometry has been used for size measurements of individual nanoparticles (NPs). Here, uncertainties in size analysis based upon two calibration approaches were evaluated: (i) the use of particle size standard and (ii) the use of ion standard solution. For particle size standard approach, the source of uncertainty to determine the target NP diameter was related to the variation in the signal intensities of both target NPs and particle size standard, and the size distribution of the particle size standard. The relative uncertainties of the 50 nm silver NP as the target were 15.0%, 9.9%, and 10.8% when particle size standards of 30 nm, 60 nm, and 100 nm silver NPs were used, respectively. As for the ion standard solution approach, the sources of uncertainty were the concentration of working standard solution, sample flow rate, transport efficiency, slope of calibration curve, and variation in the signal intensity of the ion standard solution and of the target NPs. The relative uncertainties for the 50 nm silver NP were 18.5% for 1 ng/g, 7.6% for 10 ng/g, and 4.7% for 100 ng/g solutions. The lower uncertainty obtained with a high concentration working standard solution is recommended to improve precision on particle size determinations by spICP-MS.

Mass-Dependent Critical Value Expressions for Particle Finding in Single-Particle ICP-TOFMS

In time-of-flight mass spectrometry (TOFMS), ion detection is often achieved via electron multiplication followed by fast analog-to-digital conversion (ADC). This detection approach is chosen over time-to-digital conversion because it extends the dynamic range of TOFMS measurements, especially for transient analyses. However, fast ADC detection also introduces measurement noise fundamental to the electron multiplication process. In previous research, we demonstrated that TOFMS signals acquired with fast ADC follow a compound Poisson distribution in which the Poisson-distributed arrival of ions at the detector is compounded with the response profile of the electron multiplier. Here, we consider the influence of mass-to-charge (m/z)-dependent detector responses and their impact on particle-finding accuracy in single-particle inductively coupled plasma TOFMS (spICP-TOFMS). In spICP-TOFMS, highly time-resolved ion signals are recorded and particle signals are distinguished from background signals based on thresholding the data at m/z-specific critical values. Through Monte Carlo modeling with measured m/z-dependent detector responses, we generate compound Poisson model distributions and critical values that accurately account for the dispersion of measured signals. We test the accuracy of critical values through the analysis of dissolved element solutions and comparison of measured versus predicted event rates above critical value thresholds. The use of m/z-dependent compound Poisson critical values reduces false-positive particle identifications by one to two orders of magnitude compared to thresholding criteria based on normal or Poisson statistics. The improved accuracy and robustness of compound Poisson critical values enables automated multi-element particle finding in spICP-TOFMS.

Nanomaterial Characterization in Complex Media-Guidance and Application

A broad range of inorganic nanoparticles (NPs) and their dissolved ions possess a possible toxicological risk for human health and the environment. Reliable and robust measurements of dissolution effects may be influenced by the sample matrix, which challenges the analytical method of choice. In this study, CuO NPs were investigated in several dissolution experiments. Two analytical techniques (dynamic light scattering (DLS) and inductively-coupled plasma mass spectrometry (ICP-MS)) were used to characterize NPs (size distribution curves) time-dependently in different complex matrices (e.g., artificial lung lining fluids and cell culture media). The advantages and challenges of each analytical approach are evaluated and discussed. Additionally, a direct-injection single particle (DI sp)ICP-MS technique for assessing the size distribution curve of the dissolved particles was developed and evaluated. The DI technique provides a sensitive response even at low concentrations without any dilution of the complex sample matrix. These experiments were further enhanced with an automated data evaluation procedure to objectively distinguish between ionic and NP events. With this approach, a fast and reproducible determination of inorganic NPs and ionic backgrounds can be achieved. This study can serve as guidance when choosing the optimal analytical method for NP characterization and for the determination of the origin of an adverse effect in NP toxicity.

Time-resolved ICP-MS analysis of mineral element contents and distribution patterns in spermatogenic cells of different types

Mineral elements play an important role in the spermatogenesis, maturation, and fertilization of sperm. It is of great scientific significance to study the role of mineral elements in spermatogenesis by accurately measuring the content of elements in different spermatogenic cells and analyzing the distribution pattern of elements in spermatogenesis. Here, time-resolved inductively coupled plasma mass spectrometry (ICP-MS) was used to analyze the content and distribution patterns of mineral elements in spermatogenic cells of different types at the single cell level. Firstly, spermatogonia, spermatocytes, round spermatids and elongating spermatids were successfully isolated from testis of mice of different weeks of age by differential adherent method and discontinuous bovine serum albumin (BSA) density gradient method. Then, signal profiles and elemental distributions of ²⁴Mg, ³¹P, ⁵²Cr, ⁵⁵Mn, ⁵⁶Fe and ⁶⁶Zn in spermatogenic cells were obtained with dwell time at 0.1 ms. Based on the results of acid digestion, we derived a formula to calculate element content in single cell from peak area for each element, and the feasibility and universality of the formula in the quantitative detection of single cell elements were verified by sperm samples to a certain extent. The detection results of element content in single cell showed that the content of ³¹P in elongating spermatids was significantly higher than that in spermatogonia, spermatocytes and round spermatids (P < 0.01), and the distribution range was wider. However, the ⁵²Cr and ⁵⁶Fe content of elongating spermatids was lower than that of spermatogonia, spermatocytes and round spermatids (P < 0.05). When spermatogonia developed into round spermatids, the contents of ⁵⁵Mn and ⁶⁶Zn in single cell increased significantly (P < 0.05), then decreased to the lowest in elongating spermatids. In addition, the significant decrease of ⁵²Cr, ⁵⁵Mn, ⁵⁶Fe and ⁶⁶Zn content in elongating spermatids also be visually observed from the center of the fitting curve of the element signal intensity distribution moving to the left. This study provides an elemental view of the changes in elemental content at various stages of spermatogenesis at the single-cell level. Time-resolved ICP-MS is used to detect mineral elements content and distribution patterns in spermatogenic cells of testis, which is helpful to better explore the stages and modes of action of various elements in spermatogenesis, and provide direct evidence for revealing the effects of element content changes on spermatogenesis and semen quality regulation.

Data analysis for nanoparticles characterization with single particle inductively coupled plasma mass spectrometry: From microsecond to millisecond dwell times

Single particle-inductively coupled plasma-mass spectrometry (SP-ICP-MS) has become a powerful technique for the characterization of nanoparticles (NPs). However, the accuracy of the characterization of NPs by SP-ICP-MS is greatly affected by the data acquisition rate and the way of data processing. For SP-ICP-MS analysis, ICP-MS instruments typically apply microsecond to millisecond dwell times (10 μs-10 ms). Considering the duration of one nanoparticle event in the detector is 0.4-0.9 ms, NPs will show different data forms when working with microsecond and millisecond dwell times. In this work, the effects of dwell times from microsecond to millisecond (50 μs, 100 μs, 1 ms and 5 ms) on the data forms in SP-ICP-MS analysis are discussed. The data analysis and data processing for different dwell times is discussed in detail, including the measurement of transport efficiency (TE), the distinction of signal and background, the evaluation of diameter limit of detection (LOD_d) and the quantification of mass, size and particle number concentration (PNC) of NPs. This work provides data support for the data processing process and aspects to be considered in the characterization of NPs by SP-ICP-MS, which is expected to provide guidance and reference for researchers in SP-ICP-MS analysis.

Facets of ICP-MS and their potential in the medical sciences-Part 2: nanomedicine, immunochemistry, mass cytometry, and bioassays

Inductively coupled-plasma mass spectrometry (ICP-MS) has transformed our knowledge on the role of trace and major elements in biology and has emerged as the most versatile technique in elemental mass spectrometry. The scope of ICP-MS has dramatically changed since its inception, and nowadays, it is a mature platform technology that is compatible with chromatographic and laser ablation (LA) systems. Over the last decades, it kept pace with various technological advances and was inspired by interdisciplinary approaches which endorsed new areas of applications. While the first part of this review was dedicated to fundamentals in ICP-MS, its hyphenated techniques and the application in biomonitoring, isotope ratio analysis, elemental speciation analysis, and elemental bioimaging, this second part will introduce relatively current directions in ICP-MS and their potential to provide novel perspectives in the medical sciences. In this context, current directions for the characterisation of novel nanomaterials which are considered for biomedical applications like drug delivery and imaging platforms will be discussed while considering different facets of ICP-MS including single event analysis and dedicated hyphenated techniques. Subsequently, immunochemistry techniques will be reviewed in their capability to expand the scope of ICP-MS enabling analysis of a large range of biomolecules alongside elements. These methods inspired mass cytometry and imaging mass cytometry and have the potential to transform diagnostics and treatment by offering new paradigms for personalised medicine. Finally, the interlacing of immunochemistry methods, single event analysis, and functional nanomaterials has opened new horizons to design novel bioassays which promise potential as assets for clinical applications and larger screening programs and will be discussed in their capabilities to detect low-level proteins and nucleic acids.

Distribution of Platinum and Palladium between Dissolved, Nanoparticulate, and Microparticulate Fractions of Road Dust

Ageing processes of vehicle catalytic converters inevitably lead to the release of Pt and Pd into the environment, road dust being the main sink. Though Pt and Pd are contained in catalytic converters in nanoparticulate metallic form, under environmental conditions, they can be transformed into toxic dissolved species. In the present work, the distribution of Pt and Pd between dissolved, nanoparticulate, and microparticulate fractions of Moscow road dust is assessed. The total concentrations of Pt and Pd in dust vary in the ranges 9-142 ng (mean 35) and 155-456 (mean 235) ng g^-1, respectively. The nanoparticulate and dissolved species of Pt and Pd in dust were studied using single particle inductively coupled plasma mass spectrometry. The median sizes of nanoparticulate Pt and Pd were 7 and 13 nm, respectively. The nanoparticulate fraction of Pt and Pd in Moscow dust is only about 1.6-1.8%. The average contents of dissolved fraction of Pt and Pd are 10.4% and 4.1%, respectively. The major fractions of Pt and Pd (88-94%) in road dust are associated with microparticles. Although the microparticulate fractions of Pt and Pd are relatively stable, they may become dissolved under changing environmental conditions and, hence, transformed into toxic species.

High-Throughput Sizing, Counting, and Elemental Analysis of Anisotropic Multimetallic Nanoparticles with Single-Particle Inductively Coupled Plasma Mass Spectrometry

Nanoparticles (NPs) have wide applications in physical and chemical processes, and their individual properties (e.g., shape, size, and composition) and ensemble properties (e.g., distribution and homogeneity) can significantly affect the performance. However, the extrapolation of information from a single particle to the ensemble remains a challenge due to the lack of suitable techniques. Herein, we report a high-throughput single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS)-based protocol to simultaneously determine the size, count, and elemental makeup of several thousands of (an)isotropic NPs independent of composition, size, shape, and dispersing medium with atomistic precision in a matter of minutes. By introducing highly diluted nebulized aqueous dispersions of NPs directly into the plasma torch of an ICP-MS instrument, individual NPs are atomized and ionized, resulting in ion plumes that can be registered by the mass analyzer. Our proposed protocol includes a phase transfer step for NPs synthesized in organic media, which are otherwise incompatible with ICP-MS instruments, and a modeling tool that extends the measurement of particle morphologies beyond spherical to include cubes, truncated octahedra, and tetrahedra, exemplified by anisotropic Cu NPs. Finally, we demonstrate the versatility of our method by studying the doping of bulk-dilute (<1 at. %) CuAg nanosurface alloys as well as the ease with which ensemble composition distributions of multimetallic NPs (i.e., CuPd and CuPdAg) can be obtained providing different insights in the chemistry of nanomaterials. We believe our combined protocol could deepen the understanding of macroscopic phenomena involving nanoscale structures by bringing about a statistics renaissance in research areas including, among others, materials science, materials chemistry, (nano)physics, (nano)photonics, catalysis, and electrochemistry.

Size characterization of nanomaterials in environmental and biological matrices through non-electron microscopic techniques

Engineered nanomaterials (ENs) can enter the environment, and accumulate in food chains, thereby causing environmental and health problems. Size characterization of ENs is critical for further evaluating the interactions among ENs in biological and ecological systems. Although electron microscope is a powerful tool in obtaining the size information, it has limitations when studying nanomaterials in complex matrices. In this review, we summarized non-electron microscope-based techniques, including chromatography-based, mass spectrometry-based, synchrotron radiation- and neutron-based techniques for detecting the size of ENs in environmental and biological matrices. The advantages and disadvantages of these techniques were highlighted. The perspectives on size characterization of ENs in complex matrices were also presented.

Discrimination and Quantification of Soil Nanoparticles by Dual-Analyte Single Particle ICP-QMS

This study presents the new application of dual-analyte single particle inductively coupled plasma quadrupole mass spectrometry (spICP-QMS) to the discrimination and quantification of two typical soil nanoparticles (kaolinite and goethite nanoparticles, abbr. KNPs and GNPs) in three samples (SA, SB, and SC) with three detection events (Al unpaired event, Fe unpaired event, and paired event). SA was mainly composed of KNPs with a concentration of 28 443 ± 817 particle mL^-1 and a mean particle size of 140.7 ± 0.2 nm. SB was mainly composed of GNPs with a concentration of 39 283 ± 702 particle mL^-1 and a mean particle size of 141.8 ± 2.9. In SC, the concentrations of KNPs and GNPs were 22 4541 ± 1401 and 70 604 ± 1623 particle mL^-1, respectively, and the mean particle sizes of KNPs and GNPs were 140.7 ± 0.2 and 60.2 ± 0.3 nm, respectively. The accuracy of dual-analyte spICP-QMS was determined by spiking experiments, comparing these results with the measurements of other techniques, analyzing the samples in different SA and SB proportions and in different SC concentrations. Our results demonstrated that the dual-analyte spICP-QMS is a promising approach to distinguishing different kinds of natural NPs in soils.

Analysis of Ti- and Pb-based particles in the aqueous environment of Melbourne (Australia) via single particle ICP-MS

The analysis of natural and anthropogenic nanomaterials (NMs) in the environment is challenging and requires methods capable to identify and characterise structures on the nanoscale regarding particle number concentrations (PNCs), elemental composition, size, and mass distributions. In this study, we employed single particle inductively coupled plasma-mass spectrometry (SP ICP-MS) to investigate the occurrence of NMs in the Melbourne area (Australia) across 63 locations. Poisson statistics were used to discriminate between signals from nanoparticulate matter and ionic background. TiO2-based NMs were frequently detected and corresponding NM signals were calibated with an automated data processing platform. Additionally, a method utilising a larger mass bandpass was developed to screen for particulate high-mass elements. This procedure identified Pb-based NMs in various samples. The effects of different environmental matrices consisting of fresh, brackish, or seawater were mitigated with an aerosol dilution method reducing the introduction of salt into the plasma and avoiding signal drift. Signals from TiO2- and Pb-based NMs were counted, integrated, and subsequently calibrated to determine PNCs as well as mass and size distributions. PNCs, mean sizes, particulate masses, and ionic background levels were compared across different locations and environments.

Evaluation of collision/reaction gases in single-particle ICP-MS for sizing selenium nanoparticles and assessment of their antibacterial activity

Selenium nanoparticles (SeNPs) have recently attracted attention because they combine the benefits of Se and lower toxicity compared to other chemical forms of this element. In this study, SeNPs were synthesized by a green method using ascorbic acid as the reducing agent and polyvinyl alcohol as stabilizer. The nanoparticles were widely characterized. To determine the total concentration of Se by ICP-MS, several isotopes and the use of He as collision gas were evaluated, which was effective in minimizing interferences. A method for sizing SeNPs by single particle ICP-MS (SP-ICP-MS) was developed. For this purpose, He and H₂were evaluated as collision/reaction gases, and the second one showed promising results, providing an average diameter of 48 nm for the SeNPs. These results agree with those obtained by TEM (50.1 nm). Therefore, the SP-ICP-MS can be implemented for characterizing SeNPs in terms of size and size distribution, being an important analytical tool for Se and other widely studied nanoparticles (e.g. Ag, Au, Ce, Cu, Fe, Zn). Finally, the antibacterial activity of SeNPs was assessed. The SeNPs showed bacteriostatic activity against three strains of Gram-positive bacteria and were particularly efficient in inhibiting the growthE. faecaliseven at very low concentrations (MIC < 1.4 mg l^-1). In addition, a bactericidal activity of SeNPs againstS. aureuswas observed. These nanoparticles may have potential application in pharmaceutical industry, biomedicine and agriculture.

Living in a transient world: ICP-MS reinvented via time-resolved analysis for monitoring single events

After 40 years of development, inductively coupled plasma-mass spectrometry (ICP-MS) can hardly be considered as a novel technique anymore. ICP-MS has become the reference when it comes to multi-element bulk analysis at (ultra)trace levels, as well as to isotope ratio determination for metal(loid)s. However, over the last decade, this technique has managed to uncover an entirely new application field, providing information in a variety of contexts related to the individual analysis of single entities (e.g., nanoparticles, cells, or micro/nanoplastics), thus addressing new societal challenges. And this profound expansion of its application range becomes even more remarkable when considering that it has been made possible in an a priori simple way: by providing faster data acquisition and developing the corresponding theoretical substrate to relate the time-resolved signals thus obtained with the elemental composition of the target entities. This review presents the underlying concepts behind single event-ICP-MS, which are needed to fully understand its potential, highlighting key areas of application (e.g., single particle-ICP-MS or single cell-ICP-MS) as well as of future development (e.g., micro/nanoplastics).

Evaluation of the Potential of Single Particle ICP-MS for the Accurate Measurement of the Number Concentration of AuNPs of Different Sizes and Coatings

Single particle inductively coupled plasma-mass spectrometry (spICP-MS) is an emerging technique that is capable of simultaneous measurement of the size and number concentration of metal-containing nanoparticles (NPs) at environmentally relevant levels. Although spICP-MS is widely applied to different fields, challenges remain in obtaining accurate and consistent particle number concentration (PNC) measurements. This paper presents, for the first time, a rigorous assessment of spICP-MS capabilities for measuring the PNC of gold NP (AuNP) suspensions of different sizes and coatings. The calibration of spICP-MS was accomplished with the National Institute of Standards and Technology (NIST) AuNP reference material (RM) 8013. The comparability of both spICP-MS direct and derived determination of PNC and reference PNC derived based on the mean particle size or the particle size distribution obtained by different reference sizing techniques was first assessed for NIST AuNP RM 8012, nominal diameter 30 nm. To enable a proper assessment of the accuracy of the spICP-MS results, a comprehensive estimation of the expanded uncertainty for PNC determination was carried out. Regardless of NP size or coating, a good agreement (90-110%) between spICP-MS direct determination of PNC and reported PNCs was obtained for all of the suspensions studied only when reliable in-house Au mass fractions and thorough mean particle size determinations were included in the calculation of the derived PNCs. The use of the particle size distribution over the mean size to derive PNCs resulted in larger differences for materials with a low contribution (<2%) of smaller NPs (30 nm), materials with a higher polydispersity (100 nm), or materials with two distinct subpopulations of particles (60 nm), regardless of NP coating.

Titanium nanoparticles fate in small-sized watersheds under different land-uses

Surface waters from three catchments having contrasting land-uses (forested, agricultural, and urban) were sampled monthly and analysed for nanoparticulate titanium dioxide (NPs-TiO₂) by single particle ICPMS and electron microscopy. We report one-year of data for NPs-TiO₂ having average number and mass concentrations of 9.1 × 10⁸ NPs-TiO₂ particles L^-1 and 11 µg NPs-TiO₂ L^-1 respectively. An increase in concentration during warmer months is observed in the forested and agricultural catchments. Both concentrations of NPs-TiO₂ are within the range of recently reported values using similar analytical approaches. The positive correlations for NPs-TiO₂ mass concentration or particle number with the concentration of some trace elements and DOC in the forested and agricultural catchments suggest the detected NPs-TiO₂ in these two systems are mostly from geogenic origin. Additionally, microscopy imaging confirmed the presence of NPs in the three catchments. Furthermore, the land-area normalized annual flux of NPs-TiO₂ (1.65 kg TiO₂ year^-1 km^-2) was highest for the agricultural catchment, suggesting that agricultural practices have a different impact on the NPs-TiO₂ dynamics and exports than other land-uses (urban or forestry). A similar trend is also found by the reanalysis of recent literature data.

Use of single particle inductively coupled plasma mass spectrometry for understanding the formation of bimetallic nanoparticles

Bimetallic nanoparticles (NPs), including core-shell structure and bimetallic alloy nanoparticles, were synthesized and characterized using flow field-flow fractionation (FlFFF), single particle inductively coupled plasma mass spectrometry (SP-ICP-MS), and transmission electron microscope (TEM) with energy-dispersive x-ray spectroscopy (EDS). For the core-shell particles, a nominal 80 nm commercial core-shell AuAg bimetallic nanoparticle was used to examine the applicability of SP-ICP-MS to determine the core size of Au and shell thickness of Ag. Then, the method was applied to estimate the core size of Au and shell thickness of Ag for the laboratory synthesized particles. The results were compared with those obtained from TEM-EDS. For the alloy nanoparticles, two synthesis protocols, based on the galvanic replacement of Ag seed particles with Au, were used. One was to prepare a hollow AgAu particle by varying the volume of dissolved Au in basic solution (K-gold) to etch some parts of AgNPs to dissolved ionic silver with the formation of AuNPs covering the remaining AgNPs, producing a hole inside the core nanoparticles. Another protocol was to prepare AgAu alloy nanoparticles. SP-ICP-MS was used in combination with FlFFF to provide information on the changes of particle size with varying volume of K-gold reagent. Hydrodynamic diameter increased with increasing K-gold, as observed by FlFFF. With SP-ICP-MS without prior FlFFF, bimodal distributions were observed in the size distribution of Au and Ag. With prior FlFFF, monomodal distributions were observed by SP-ICP-MS, which allow the use of particle concentration and size to estimate the mass concentration of elements on the fractionated bimetallic nanoparticles. This study illustrates the potential use of SP-ICP-MS for gaining information about particle transformation during the synthesis of bimetallic nanoparticles.

Nanospeciation of metals and metalloids in volcanic ash using single particle inductively coupled plasma mass spectrometry

Volcanic activity is one of the main sources of natural nanoparticles. It has been found earlier that the concentration of toxic metals/metalloids in nanoparticles of volcanic ash may be one or two orders of magnitude higher than in bulk sample. However, fate and behavior of toxic metals/metalloids depend on the type of their binding to nanoparticles. Hence, element species adsorbed onto pyroclastic nanoparticles and individual nanophases of metal/metalloid oxides or salts should be distinguished. For the first time, the single particle inductively coupled plasma mass spectrometry has been applied to the nanospeciation of volcanic particles. Ashes of four volcanoes of Kamchatka (Russia) were under study. Nanoparticles were separated from bulk ash samples using coiled-tube field-flow fractionation. It has been shown that the nanospeciation of Ni, Zn, Ag, Cd, Tl, As, Pb, Bi, Te, and Hg is dependent on element and volcano. In most cases these elements can be found both as species absorbed onto pyroclastic nanoparticles and as individual nanophases. The ratios of individual nanophases and adsorbed species vary with the sample. In nanoparticles of Tolbachik volcano ash, Ni, Zn, Tl, and Hg are present only as individual nanophases, while Bi, As, Pb, Ag, Cd, and Te are found both as adsorbed species and individual nanophases. The results obtained open a new door into study on the chemical composition of volcanic ash nanoparticles and their fate in the environment.

Enzyme digestion combined with SP-ICP-MS analysis to characterize the bioaccumulation of gold nanoparticles by mustard and lettuce plants

Plants can absorb and accumulate engineered nanomaterials (ENMs) through water and soil, providing a potential way for nanoparticles to be enriched in humans through the food chain. In this paper, a combination of enzymatic digestion method and SP-ICP-MS analysis was used to quantitatively characterize the enriched AuNPs in mustard and lettuce plants. The results showed that Macerozyme R-10 enzyme can extract AuNPs from plants without obvious aggregation/dissolution. Both mustard and lettuce plants can absorb and enrich the complete AuNPs to the above-ground organs, and the particle number concentrations detected are 1.24 × 107 particles L-1 and 4.39 × 107 particles L-1, respectively. With different exposure level of AuNPs(0.5 mg L-1,), a particle number concentration of 2.32 × 107 particles L-1 was detected in the stems of lettuce plants, while the mustard failed to transport AuNPs to the above-ground organs. The transport efficiency of Au ions by plants is higher than that of AuNPs, and the plants have stronger bioavailability for ions.

Single virus inductively coupled plasma mass spectroscopy analysis: A comprehensive study

The characterisation of individual nanoparticles by single particle ICP-MS (SP-ICP-MS) has paved the way for the analysis of smallest biological systems. This study suggests to adapting this method for single viruses (SV) identification and counting. With high resolution multi-channel sector field (MC SF) ICP-MS records in SV detection mode, the counting of master and key ions can allow analysis and identification of single viruses. The counting of 2-500 virial units can be performed in 20 s. Analyses are proposed to be carried out in Ar torch for master ions: ¹²C⁺, ¹³C⁺, ¹⁴N⁺, ¹⁵N⁺, and key ions ³¹P⁺, ³²S⁺, ³³S⁺ and ³⁴S⁺. All interferences are discussed in detail. The use of high resolution SF ICP-MS is recommended while options with anaerobic/aerobic atmospheres are explored to upgrade the analysis when using quadrupole ICP-MS. Application for two virus types (SARS-COV2 and bacteriophage T5) is investigated using time scan and fixed mass analysis for the selected virus ions allowing characterisation of the species using the N/C, P/C and S/C molar ratio's and quantification of their number concentration.

Synthesis, Characterization, Applications, and Toxicity of Green Synthesized Nanoparticles

Nanotechnology is a cutting-edge area with numerous industrial applications. Nanoparticles are structures that have dimensions ranging from 1-100 nm which exhibit significantly different mechanical, optical, electrical, and chemical properties when compared with their larger counterparts. Synthetic routes that use natural sources, such as plant extracts, honey, and microorganisms are environmentally friendly and low-cost methods that can be used to obtain nanoparticles. These methods of synthesis generate products that are more stable and less toxic than those obtained using conventional methods. Nanoparticles formed by titanium dioxide, zinc oxide, silver, gold, and copper, as well as cellulose nanocrystals are among the nanostructures obtained by green synthesis that have shown interesting applications in several technological industries. Several analytical techniques have also been used to analyze the size, morphology, hydrodynamics, diameter, and chemical functional groups involved in the stabilization of the nanoparticles as well as to quantify and evaluate their formation. Despite their pharmaceutical, biotechnological, cosmetic, and food applications, studies have detected their harmful effects on human health and the environment; and thus, caution must be taken in uses involving living organisms. The present review aims to present an overview of the applications, the structural properties, and the green synthesis methods that are used to obtain nanoparticles, and special attention is given to those obtained from metal ions. The review also presents the analytical methods used to analyze, quantify, and characterize these nanostructures.

Optimisation and application of an analytical approach for the characterisation of TiO2 nanoparticles in food additives and pharmaceuticals by single particle inductively coupled plasma-mass spectrometry

This study was designed to optimise an analytical method for characterising TiO₂ nanoparticles (NPs) in food additives and pharmaceuticals by inductively coupled plasma-mass spectrometry in single particle mode (spICP-MS). Several parameters, including transport efficiency (TE), were assessed and optimised using the NM-100 reference material. We found that self-aspiration for sample intake and use of the concentration-based method for TE was optimal for characterising TiO₂ NPs. No spectral interference was observed with either ⁴⁹Ti or ⁴⁸Ti isotopes. The optimised Excel spreadsheet developed for this study not only provided additional parameters but gave results closer to the NM-100 reference value than the ICP-MS software. The method was then applied to the analysis of a selection of food samples and pharmaceuticals. The average diameter of TiO₂ particles ranged from 86 to 179 nm in the food samples and from 131 to 197 nm in the pharmaceuticals, while the nanoparticular fraction was between 19 and 68% in food, and between 13 and 45% in pharmaceuticals.

Characterisation of selenium and tellurium nanoparticles produced by Aureobasidium pullulans using a multi-method approach

Aureobasidium pullulans was grown in liquid culture media amended with selenite and tellurite and selenium (Se) and tellurium (Te) nanoparticles (NPs) were recovered after 30 d incubation. A separation method was applied to recover and characterise Se and Te NPs by asymmetric flow field flow fractionation (AF4) with online coupling to multi-angle light scattering (MALS), ultraviolet visible spectroscopy (UV-Vis), and inductively coupled plasma mass spectrometry (ICP-MS) detectors. Additional characterisation data was obtained from transmission electron microscopy (TEM), and dynamic light scattering (DLS). Solutions of 0.2% Novachem surfactant and 10 mM phosphate buffer were compared as mobile phases to investigate optimal AF4 separation and particle recovery using Se-NP as a model sample. 88% recovery was reported for 0.2% Novachem solution, compared with 50% recovery for phosphate buffer. Different crossflow (C_flow) rates were compared to further investigate optimum separation, with recoveries of 88% and 30% for Se-NPs, and 90% and 29% for Te-NPs for 3.5 mL min^-1 and 2.5 mL min^-1 respectively. Zeta-potential (ZP) data suggested higher stability for NP elution in Novachem solution, with increased stability attributed to minimised NP-membrane interaction due to PEGylation. Detection with MALS showed monodisperse Se-NPs (45-90 nm) and polydisperse Te-NPs (5-65 nm).Single particle ICP-MS showed mean particle diameters of 49.7 ± 2.7 nm, and 135 ± 4.3 nm, and limit of size detection (LOSD) of 20 nm and 45 nm for Se-NPs and Te-NPs respectively. TEM images of Se-NPs and Te-NPs displayed a spherical morphology, with the Te-NPs showing a clustered arrangement, which suggested electrostatic attraction amongst neighbouring particles. Particle hydrodynamic diameters (d_H) measured with dynamic light scattering (DLS) further suggested monodisperse Se-NPs and polydisperse Te-NPs distributions, showing good agreement with AF4-MALS for Se-NPs, but suggests that the R_g obtained from AF4-MALS for Te-NP was unreliable. The results demonstrate a complementary application of asymmetric flow field-flow fractionation (AF4), ICP-MS, light scattering, UV-Vis detection, and microscopic techniques to characterise biogenic Se and Te NPs.

A Sensitive Single Particle-ICP-MS Method for CeO2 Nanoparticles Analysis in Soil during Aging Process

The increasing prevalence of products that incorporate engineered nanoparticles (ENPs) has prompted efforts to investigate the potential release, environmental fate, and exposure of the ENPs. However, the investigation of cerium dioxide nanoparticles (CeO₂ NPs) in soil has remained limited, owing to the analytical challenge from the soil's complex nature. In this study, this challenge was overcome by applying a novel single particle-inductively coupled plasma-mass spectrometry (SP-ICP-MS) methodology to detect CeO₂ NPs extracted from soil, utilizing tetrasodium pyrophosphate (TSPP) aqueous solution as an extractant. This method is highly sensitive for determining CeO₂ NPs in soil, with detection limits of size and concentration of 15 nm and 194 NPs mL^-1, respectively. Extraction efficiency was sufficient in the tested TSPP concentration range from 1 mM to 10 mM at a soil-to-extractant ratio 1:100 (g mL^-1) for the extraction of CeO₂ NPs from the soil spiked with CeO₂ NPs. The aging study demonstrated that particle size, size distribution, and particle concentration underwent no significant change in the aged soils for a short period of one month. This study showed an efficient method capable of extracting and accurately determining CeO₂ NPs in soil matrices. The method can serve as a useful tool for nanoparticle analysis in routine soil tests and soil research.

New Orientation: A Downward-pointing Vertical Inductively Coupled Plasma Mass Spectrometer for the Analysis of Microsamples

We present a prototype of a vertical-downward configuration of an inductively coupled plasma mass spectrometer (ICPMS) allowing the sample introduction from the top. With this novel approach to orient the ICP downward, we aim to expand the sample transport capabilities in ICPMS especially for the transport of droplets or particles with a final goal to analyze individual cells. Because of this gravity-assisted sampling approach, the transport of larger sized droplets, that is, droplets that would be difficult to transport into a horizontally oriented ICPMS, becomes possible and, furthermore, becomes independent of the droplets' size or size distribution. We demonstrate that droplets of an initial size of 70 μm can be successfully transported into the plasma at dispensing frequencies up to 1 kHz without the need for a desolvation device. In addition, we observed that the implementation of a desolvation device, that is, a gas-exchange device (GED), can improve the detection efficiencies (DEs). Compared to operating conditions that are commonly reported for ICPMS experiments, significantly different optimization parameters (radio frequency power and gas flow rates) were tested in the presented experiments here while instrument type-specific DEs were obtained.

Characterisation of particles within and aerosols produced by nano-containing consumer spray products

Nanoparticles have been incorporated into a range of consumer spray products, providing the potential for inadvertent inhalation by users and bystanders. The levels and characteristics of nanoparticle inhalation exposures arising from the use of such products are important inputs to risk assessments and informing dose regimes for in vitro and in vivo studies investigating hazard potentials. To date, only a small number of studies have been undertaken to explore both the aerosols generated from such products and the metal nanoparticles within them. The objective of the current study was to add to the limited data in this field by investigating a range of nano-containing spray products available within the UK. Six products were selected and the nanoparticles characterised using a combination of techniques, including: inductively coupled plasma mass spectrometry (ICP-MS), dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), transmission electron microscopy energy-dispersive X-ray spectroscopy (TEM-EDX) and single particle ICP-MS (spICP-MS). The aerosol produced by these products, when sprayed within a glovebox, was characterised by scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS). A cascade impactor with thirteen stages (NanoMOUDI) was used with one product to generate information on the size specific nanoparticle elemental distribution within the aerosol. The results demonstrated the presence of solid nanoparticles (silver, gold or silica) in each of the products at low concentrations (<13 ppm). TEM and (sp)ICP-MS provided reliable information on nanoparticle size, shape, number and mass, while the light scattering methods were less effective due to the complex matrices of the products and their lack of chemical specificity. The aerosols varied significantly across products, with particle and mass concentrations spanning 5 orders of magnitude (10 - 106 cm-3 and 0.3-7600 μg m-3, respectively). The NanoMOUDI results clearly indicated non-uniform distribution of silver within different aerosol particle size ranges.

Detection of nanoparticles by single-particle ICP-MS with complete transport efficiency through direct nebulization at few-microlitres-per-minute uptake rates

Measurement of nanoparticle (NP) concentration and size by single-particle inductively coupled plasma mass spectrometry (spICP-MS) usually requires the use of a NP reference material to determine the loss of NPs and/or ions during their transport from the sample solution to the detection system. The determination of this loss, qualified as nebulization efficiency (η_Nebulization) and/or transport efficiency (η_Transport), is time-consuming, costly and lacks reliability. Nebulization of the NPs directly into the plasma (without a spray chamber) results in η_Nebulization = 100% and is thus a promising strategy to avoid these calibration steps. In this work, we used the μ-dDIHEN introduction system: a demountable direct injection high-efficiency nebulizer (dDIHEN) hyphenated to a flow-injection valve and a gas displacement pump. For the first time with a continuous flow nebulizer, complete transport efficiency was reached (i.e. η_Transport = 100%). Operated at a very low uptake rate (as low as 8 μL min^-1), the μ-dDIHEN accurately and reproducibly determined average diameters of Au-, Ag- and Pt-NPs, in full agreement with their reference values. It was also successfully tested for Au-NPs in complex matrices, such as surface waters. spICP-MS analyses with the μ-dDIHEN sample introduction system only require a dissolved standard calibration to determine NP average diameter (d_NPs in nm) and number concentration (N_NPs) from the simplified set of equations: [Formula: see text] and [Formula: see text]Graphical abstract.

Determination of Total Silicon and SiO2 Particles Using an ICP-MS Based Analytical Platform for Toxicokinetic Studies of Synthetic Amorphous Silica

Synthetic amorphous silica (SAS), manufactured in pyrogenic or precipitated form, is a nanomaterial with a widespread use as food additive (E 551). Oral exposure to SAS results from its use in food and dietary supplements, pharmaceuticals and toothpaste. Recent evidence suggests that oral exposure to SAS may pose health risks and highlights the need to address the toxic potential of SAS as affected by the physicochemical characteristics of the different forms of SAS. For this aim, investigating SAS toxicokinetics is of crucial importance and an analytical strategy for such an undertaking is presented. The minimization of silicon background in tissues, control of contamination (including silicon release from equipment), high-throughput sample treatment, elimination of spectral interferences affecting inductively coupled plasma mass spectrometry (ICP-MS) silicon detection, and development of analytical quality control tools are the cornerstones of this strategy. A validated method combining sample digestion with silicon determination by reaction cell ICP-MS is presented. Silica particles are converted to soluble silicon by microwave dissolution with mixtures of HNO3, H2O2 and hydrofluoric acid (HF), whereas interference-free ICP-MS detection of total silicon is achieved by ion-molecule chemistry with limits of detection (LoDs) in the range 0.2-0.5 µg Si g-1 for most tissues. Deposition of particulate SiO2 in tissues is assessed by single particle ICP-MS.

Tackling Complex Analytical Tasks: An ISO/TS-Based Validation Approach for Hydrodynamic Chromatography Single Particle Inductively Coupled Plasma Mass Spectrometry

Nano-carrier systems such as liposomes have promising biomedical applications. Nevertheless, characterization of these complex samples is a challenging analytical task. In this study a coupled hydrodynamic chromatography-single particle-inductively coupled plasma mass spectrometry (HDC-spICP-MS) approach was validated based on the technical specification (TS) 19590:2017 of the international organization for standardization (ISO). The TS has been adapted to the hyphenated setup. The quality criteria (QC), e.g., linearity of the calibration, transport efficiency, were investigated. Furthermore, a cross calibration of the particle size was performed with values from dynamic light scattering (DLS) and transmission electron microscopy (TEM). Due to an additional Y-piece, an online-calibration routine was implemented. This approach allows the calibration of the ICP-MS during the dead time of the chromatography run, to reduce the required time and enhance the robustness of the results. The optimized method was tested with different gold nanoparticle (Au-NP) mixtures to investigate the characterization properties of HDC separations for samples with increasing complexity. Additionally, the technique was successfully applied to simultaneously determine both the hydrodynamic radius and the Au-NP content in liposomes. With the established hyphenated setup, it was possible to distinguish between different subpopulations with various NP loads and different hydrodynamic diameters inside the liposome carriers.

Improved validation for single particle ICP-MS analysis using a pneumatic nebulizer / microdroplet generator sample introduction system for multi-mode nanoparticle determination

This study reports on the development of a single-particle (sp) inductively coupled plasma mass spectrometry (ICP-MS) technique suitable for the multi-mode determination of nanoparticle (NP) metal mass fraction and number concentration. The described technique, which is based on a dual inlet system consisting of a pneumatic nebulizer (PN) and a microdroplet generator (MDG), allows for the sequential introduction of ionic metal calibrant solutions and nanoparticle suspensions via all combinations of the two inlets; thus allowing for a combination of three independent modes of analysis. A novel interface, assembled using standard analytical components (a demountable quartz ICP-MS torch, flexible non-conducting silicon tubing and various connectors), was used to interface the dual inlet system to an ICP-MS. The interface provided improved functionality, compared to a previous design. It is now possible to conveniently exchange and introduce standard solutions and samples via all inlet combinations, analyze them, and also wash the sample inlet systems while the whole setup is still connected to an operating ICP-MS. This setup provided seamless and robust operation in a total of three analysis modes, i.e. three ways to independently determine the metal mass fraction and NP number concentration. All three analyses modes could be carried out within a single analytical run lasting approximately 20 min. The unique feature of the described approach is that each analysis mode is based on a different calibration principle, thus constituting an independent way to determine metal mass fractions and nanoparticle number concentrations. Conducting the three independent state-of-the-art analysis, within a single analytical run, improves substantially the validation capabilities of sp-ICP-MS for NP analysis. To assess the technique's analytical performance, Au, Ag and CeO₂ nanoparticles were analyzed. The determined average diameters for Au (56.7 ± 1.5 nm), Ag (72.8 ± 3.4 nm) and CeO₂ (69.0 ± 6.4 nm) NPs were in close agreement for all three modes of analysis, as well as with the values provided by suppliers' for Au and Ag NPs (56.0 ± 0.5 for Au, 74.6 ± 3.8 nm for Ag). However, the determined average value for CeO₂ was much higher than the expected 28.4 ± 10.4 nm, possibly due to NP agglomeration and the inability to detect NPs existing within the lower size range. The determined NP number concentrations, using analysis modes -I and -II, gave recoveries between 91 and 100% for the Au and Ag NP number concentrations. Whereas analysis mode -III showed a recovery of 70-88% for the same materials. Because of the polydispersity, the small size and polyhedral shape of the CeO₂ NPs it was not possible to make NP number concentration comparisons for this material.

Insight into the Crucial Role of Secondary Mineral Phases in the Transfer of Gold Nanoparticles through a Sand Column Using Online ICP-MS/spICP-MS Monitoring

Investigating the transport of engineered nanoparticles through representative soils is an important issue in assessing their mobility and fate in the environment. In this study, successive injections of gold nanoparticles (AuNPs) were performed in a quartz sand column with an eluent composed of 10^-2 M NaCl at a pH of 7.5. After this series of injections, remobilization of the AuNPs was examined by raising the eluent pH to 10. ¹⁹⁷Au and the conservative ionic tracer ⁷⁹Br were monitored simultaneously by online inductively coupled plasma mass spectrometry (ICP-MS), and the particulate nature of gold eluting from the column was confirmed by setting the ICP-MS in the "single particle" mode. The extent of AuNP attachment was greater than predicted by DLVO theory considering quartz as the sole collector, decreased with the number of injections and with particle size. In contrast with the repulsive interaction energy between the particles and the quartz surface, kaolinite, a secondary mineral of the sand, provided favorable conditions for particle attachment. The superimposed signals of ¹⁹⁷Au and ²⁷Al in the column effluent after pH increase suggest that gold nanoparticles were essentially remobilized as heteroaggregates with the kaolinite colloids they were attached to when favorable conditions for clay detachment from the sand grains were encountered.

Complementary techniques (spICP-MS, TEM, and HPLC-ICP-MS) reveal the degradation of 40 nm citrate-stabilized Au nanoparticles in rat liver after intraperitoneal injection

BACKGROUND

Due to the increased use of engineered nanoparticles (NPs), their tracing in environmental and biological systems is of utmost importance. Besides their accumulation within a biological specimen, little is known about their degradation and transformation into corresponding low-molecular species that might influence any toxicological impact.

ANALYTICAL METHODS

Wistar rats underwent intraperitoneal injections of 40 nm citrate-stabilized gold nanoparticles. Different liver samples were analysed for the occurrence of nanoparticles and potential degradation products by means of spICP-MS, TEM and HPLC-ICP-MS.

MAIN FINDINGS

Studies using spICP-MS revealed the presence of the originally administrated Au NPs (40 nm diameter) and some evidences of other Au-containing species due to the increased background signal. Images obtained by transmission electron microscopy (TEM) showed the predominant presence of particles of significantly smaller diameter (6 ± 2 nm). As complementary method, HPLC-ICP-MS confirmed the presence of both particle types indicating a degradation of the Au NPs accompanied by detection of low-molecular Au species.

CONCLUSIONS

This study underlines that degradation of gold nanoparticles to low-molecular gold species might have to be taken into account in future for studies on their toxicological behaviour and their potential use in clinical applications.