Nanoparticles as a younger member of the trace element species family - a food perspective

Speciation analysis plays a key role in understanding the biological activity and toxicity of an element. So far, classical speciation analysis focused only on the dissolved fraction of an elemental species, whereas nanoparticle forms of analytes are being widely found in consumer and industrial products. A significant contributor to human exposure to nanoparticles is through food into which nanoparticles can be incorporated from endogenous sources or they may be formed naturally in the living organisms. Nanoparticles often undergo changes in the food matrices and upon consumption, in the gastrointestinal tract, which present a significant challenge to their characterisation. Therefore, a combination of both classical and nanoparticle speciation analytical techniques is needed for the characterisation of both dissolved and particulate forms of the chemical species. This article presents and discusses the current trends in analysis of nanoparticle behaviour in the gastrointestinal tract and formation and characterisation of biogenic nanoparticles.

Determination of selenium-containing species, including nanoparticles, in selenium-enriched Lingzhi mushrooms

Mushrooms are considered a valuable food source due to their high protein and fibre and low fat content, among the other health benefits of their consumption. Selenium is an essential nutrient and is renowned for its chemo-preventative properties. In this study, batches of selenium-enriched Lingzhi mushrooms were prepared by growing mycelium and fruit in substrates containing various concentrations of sodium selenite. The mushroom fruit accumulated low levels of selenium with selenomethionine being the most abundant form in all enriched samples. Conversely, the mycelium showed significant selenium accumulation but relatively low proportions of selenomethionine. The red colour of the selenium-enriched mycelia indicated the probable presence of selenium nanoparticles, which was confirmed by single-particle inductively coupled plasma-mass spectrometry. Mean particle diameters of 90-120 nm were observed, with size distributions of 60-250 nm. Additional analysis with transmission electron microscopy confirmed this size distribution and showed that the biogenic selenium nanoparticles were roughly spherical in shape and contained elemental selenium.

Advances in selenium supplementation: From selenium-enriched yeast to potential selenium-enriched insects, and selenium nanoparticles

Selenium (Se) is an essential micronutrient that plays an important role in animal and human development and physiological homoeostasis. This review surveys the role of Se in the environment, plants and animal bodies, and discusses data on Se biofortification with different sources of supplementation, from inorganic to organic forms, with special focus on Se-enriched yeast (Se-yeast). Although Se-yeast remains one of the main sources of organic Se, other emerging and innovative sources are reviewed, such as Se-enriched insects and Se-nanoparticles and their potential use in animal nutrition. Se-enriched insects are discussed as an option for supplying Se in organic form to livestock diets. Se-nanoparticles are also discussed, as they represent a more biocompatible and less toxic source of inorganic Se for animal organisms, compared to selenite and selenate. We also provide up to date information on the legal framework in the EU, USA, and Canada of Se that is contained in feed additives. From the scientific evidence available in the literature, it can be concluded that among the inorganic forms, sodium selenite is still one of the main options, whereas Se-yeast remains the primary organic form. However, other potential sources such as Se-enriched insects and Se-nanoparticles are being investigated as they could potentially combine a high bioavailability and reduced Se emissions in the environment.

Selenite Bioremediation by Food-Grade Probiotic Lactobacillus casei ATCC 393: Insights from Proteomics Analysis

Microorganisms capable of converting toxic selenite into elemental selenium (Se0) are considered an important and effective approach for bioremediation of Se contamination. In this study, we investigated the mechanism of reducing selenite to Se0 and forming Se nanoparticles (SeNPs) by food-grade probiotic Lactobacillus casei ATCC 393 (L. casei ATCC 393) through proteomics analysis. The results showed that selenite added during the exponential growth period of bacteria has the highest reduction efficiency, and 4.0 mM selenite decreased by nearly 95% within 72 h and formed protein-capped-SeNPs. Proteomics analysis revealed that selenite induced a significant increase in the expression of glutaredoxin, oxidoreductase, and ATP binding cassette (ABC) transporter, which can transport glutathione (GSH) and selenite. Selenite treatment significantly increased the CydC and CydD (putative cysteine and glutathione importer, ABC transporter) mRNA expression level, GSH content, and GSH reductase activity. Furthermore, supplementation with an additional GSH significantly increased the reduction rate of selenite, while GSH depletion significantly inhibited the reduction of selenite, indicating that GSH-mediated Painter-type reaction may be the main pathway of selenite reduction in L. casei ATCC 393. Moreover, nitrate reductase also participates in the reduction process of selenite, but it is not the primary factor. Overall, L. casei ATCC 393 effectively reduced selenite to SeNPs by GSH and nitrate reductase-mediated reduction pathway, and the GSH pathway played the decisive role, which provides an environmentally friendly biocatalyst for the bioremediation of Se contamination. IMPORTANCE Due to the high solubility and bioavailability of selenite, and its widespread use in industrial and agricultural production, it is easy to cause selenite to accumulate in the environment and reach toxic levels. Although the bacteria screened from special environments have high selenite tolerance, their safety has not been fully verified. It is necessary to screen out strains with selenite-reducing ability from nonpathogenic, functionally known, and widely used strains. Herein, we found food-grade probiotic L. casei ATCC 393 effectively reduced selenite to SeNPs by GSH and nitrate reductase-mediated reduction pathway, which provides an environmentally friendly biocatalyst for the bioremediation of Se contamination.

Single-cell ICP-MS for studying the association of inorganic nanoparticles with cell lines derived from aquaculture species

The current research deals with the use of single-cell inductively coupled plasma-mass spectrometry (scICP-MS) for the assessment of titanium dioxide nanoparticle (TiO₂ NP) and silver nanoparticle (Ag NP) associations in cell lines derived from aquaculture species (sea bass, sea bream, and clams). The optimization studies have considered the avoidance of high dissolved background, multi-cell peak coincidence, and possible spectral interferences. Optimum operating conditions were found when using a dwell time of 50 μs for silver and 100 μs for titanium. The assessment of associated TiO₂ NPs by scICP-MS required the use of ammonia as a reaction gas (flow rate at 0.75 mL min^-1) for interference-free titanium determinations (measurements at an m/z ratio of 131 from the ⁴⁸Ti(NH)(NH₃)₄ adduct). The influence of other parameters such as the number of washing cycles and the cell concentration on accurate determinations by scICP-MS was also fully investigated. Cell exposure trials were performed using PVP-Ag NPs (15 and 100 nm, nominal diameter) and citrate-TiO₂ NPs (5, 25, and 45 nm, nominal diameter) at nominal concentrations of 10 and 50 μg mL^-1 for citrate-TiO₂ NPs and 5.0 and 50 μg mL^-1 for PVP-Ag NPs. Results have shown that citrate-TiO₂ NPs interact with the outer cell membranes, being quite low in the number of citrate-TiO₂ NPs that enters the cells (the high degree of aggregation is the main factor which leads to the aggregates being in the extracellular medium). In contrast, PVP-Ag NPs have been found to enter the cells.

Single-cell ICP-MS to address the role of trace elements at a cellular level

The heterogeneity properties shown by cells or unicellular organisms have led to the development of analytical methods at the single-cell level. In this sense, considering the importance of trace elements in these biological systems, the inductively coupled plasma mass spectrometer (ICP-MS) configured for analyzing single cell has presented a high potential to assess the evaluation of elements in cells. Moreover, advances in instrumentation, such as coupling laser ablation to the tandem configuration (ICP-MS/MS), or alternative mass analyzers (ICP-SFMS and ICP-TOFMS), brought significant benefits, including sensitivity improvement, high-resolution imaging, and the cell fingerprint. From this perspective, the single-cell ICP-MS has been widely reported in studies involving many fields, from oncology to environmental research. Hence, it has contributed to finding important results, such as elucidating nanoparticle toxicity at the cellular level and vaccine development. Therefore, in this review, the theory of single-cell ICP-MS analysis is explored, and the applications in this field are pointed out. In addition, the instrumentation advances for single-cell ICP-MS are addressed.

The influence of H 2 partial pressure on biogenic palladium nanoparticle production assessed by single‐cell ICP ‐mass spectrometry

The production of biogenic palladium nanoparticles (bio-Pd NPs) is widely studied due to their high catalytic activity, which depends on the size of nanoparticles (NPs). Smaller NPs (here defined as <100 nm) are more efficient due to their higher surface/volume ratio. In this work, inductively coupled plasma-mass spectrometry (ICP-MS), flow cytometry (FCM) and transmission electron microscopy (TEM) were combined to obtain insight into the formation of these bio-Pd NPs. The precipitation of bio-Pd NPs was evaluated on a cell-per-cell basis using single-cell ICP-MS (SC-ICP-MS) combined with TEM images to assess how homogenously the particles were distributed over the cells. The results provided by SC-ICP-MS were consistent with those provided by "bulk" ICP-MS analysis and FCM. It was observed that heterogeneity in the distribution of palladium over an entire cell population is strongly dependent on the Pd²⁺ concentration, biomass and partial H₂ pressure. The latter three parameters affected the particle size, ranging from 15.6 to 560 nm, and exerted a significant impact on the production of the bio-Pd NPs. The TEM combined with SC-ICP-MS revealed that the mass distribution for bacteria with high Pd content (144 fg Pd cell^-1 ) indicated the presence of a large number of very small NPs (D50 = 15.6 nm). These results were obtained at high cell density (1 × 10⁵  ± 3 × 10⁴ cells μl^-1 ) and H₂ partial pressure (180 ml H₂ ). In contrast, very large particles (D50 = 560 nm) were observed at low cell density (3 × 10⁴  ± 10 × 10² cells μl^-1 ) and H₂ partial pressure (10-100 ml H₂ ). The influence of the H₂ partial pressure on the nanoparticle size and the possibility of size-tuned nanoparticles are presented.

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.

Current Methods and Prospects for Analysis and Characterization of Nanomaterials in the Environment

Analysis and characterization of naturally occurring and engineered nanomaterials in the environment are critical for understanding their environmental behaviors and defining real exposure scenarios for environmental risk assessment. However, this is challenging primarily due to the low concentration, structural heterogeneity, and dynamic transformation of nanomaterials in complex environmental matrices. In this critical review, we first summarize sample pretreatment methods developed for separation and preconcentration of nanomaterials from environmental samples, including natural waters, wastewater, soils, sediments, and biological media. Then, we review the state-of-the-art microscopic, spectroscopic, mass spectrometric, electrochemical, and size-fractionation methods for determination of mass and number abundance, as well as the morphological, compositional, and structural properties of nanomaterials, with discussion on their advantages and limitations. Despite recent advances in detecting and characterizing nanomaterials in the environment, challenges remain to improve the analytical sensitivity and resolution and to expand the method applications. It is important to develop methods for simultaneous determination of multifaceted nanomaterial properties for in situ analysis and characterization of nanomaterials under dynamic environmental conditions and for detection of nanoscale contaminants of emerging concern (e.g., nanoplastics and biological nanoparticles), which will greatly facilitate the standardization of nanomaterial analysis and characterization methods for environmental samples.

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.

Detection of Histidine-Tagged Protein in Escherichia coli by Single-Cell Inductively Coupled Plasma-Mass Spectrometry

We have developed a rapid and precise quantification method for a histidine (His)-tagged recombinant protein produced in Escherichia coli (E. coli) by single-cell inductively coupled plasma-mass spectrometry (SC-ICP-MS). Plasmid vector containing enhanced green fluorescent protein (EGFP) or red fluorescent protein (mCherry) gene fused with His-tag was transformed into E. coli. The transformed E. coli was exposed to nickel (Ni) chloride or cobalt (Co) chloride for labeling His-tag with the Ni or Co ion. Then, E. coli was analyzed by SC-ICP-MS to determine the amount of EGFP or mCherry protein on the basis of the signal of Ni or Co bound to His-tag. By comparing Ni and Co contents in E. coli expressing His-tagged mCherry with those in nontagged mCherry, the specific binding of Co to His-tag was more clearly detected than that of Ni. The Co contents were increased until 6 h after the protein induction, and this observation was coincident with the increases in fluorescence intensity of EGFP or mCherry measured by a flow cytometer. However, the Co contents were decreased for EGFP and kept at a constant level for mCherry from 6 to 24 h despite the continuous increase in the fluorescence intensity through incubation. The fluorescent proteins were mainly recovered in the insoluble fraction 24 h after the induction. This can be explained by the fact that the overexpressed fluorescent proteins with His-tag are transferred into inclusion bodies, which hampers the binding of the fluorescent proteins to the Co ion. SC-ICP-MS can be a useful technique to precisely quantify soluble recombinant proteins in E. coli without the extraction and purification process.

Absolute Quantification of Nanoparticle Interactions with Individual Human B Cells by Single Cell Mass Spectrometry

We report on the absolute quantification of nanoparticle interactions with individual human B cells using quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS). This method enables the quantification of nanoparticle-cell interactions at single nanoparticle and single cell levels. We demonstrate the efficient and accurate detection of individually suspended B cells and found an ∼100-fold higher association of colloidally stable positively charged nanoparticles with single B cells than neutrally charged nanoparticles. We confirmed that these nanoparticles were internalized by individual B cells and determined that the internalization occurred via energy-dependent pathways consistent with endocytosis. Using dual analyte ICP-MS, we determined that >80% of single B cells were positive for nanoparticles. Our study demonstrates an ICP-MS workflow for the absolute quantification of nanoparticle-cell interactions with single cell and single nanoparticle resolution. This unique workflow could inform the rational design of various nanomaterials for controlling cellular interactions, including immune cell-nanoparticle interactions.

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 copper uptake in individual spores of Streptomyces coelicolor and endogenic nanoparticles formation to modulate the secondary metabolism

Copper modulates secondary metabolism in Streptomyces. Although the cytosolic copper concentration is controlled by several chaperones and transporters, the formation of copper nanoparticles and its relation to the antibiotic production has never been established in the model Streptomyces coelicolor. In this work, state-of-the-art analytical tools are used to evaluate the incorporation of copper in individual spores of Streptomyces coelicolor at different exposure concentrations (40, 80 and 160 µM Cu). Among them, the use of single cell-inductively coupled plasma-mass spectrometry (SC-ICP-MS) revealed incorporation levels in the range of 2 to 2.5 fg/spore (median) increasing up to 4.75 fg/spore at the upper exposure concentrations. The copper storage within the spores in the form of nanoparticles was evaluated using a combination of single particle-ICP-MS (sp-ICP-MS) and transmission electron microscopy (TEM). The obtained data confirmed the presence of nanoparticles in the range of 8 to 40 (mean size 21 nm) inside S. coelicolor spores. The presence of the nanoparticles was correlated with the actinorhodin production in liquid non-sporulating cultures amended with up to 80 µM Cu. However, further increase to 160 µM Cu, yielded to a significant decrease in antibiotic production. Secondary metabolism is activated under stressful conditions and cytosolic copper seems to be one of the signals triggering antibiotic production. Particularly, nanoparticle formation might contribute to modulate the secondary metabolism and prevent for copper toxicity. This work describes, for first time, the formation of endogenous copper nanoparticles in S. coelicolor and reveals their correlation with the secondary metabolism.

Single-event tandem ICP-mass spectrometry for the quantification of chemotherapeutic drug-derived Pt and endogenous elements in individual human cells

Single cell - tandem ICP-mass spectrometry (SC-ICP-MS/MS) was used for the determination of the absolute amount of Pt (coming from exposure to various concentration levels of cisplatin as a chemotherapeutic drug) and five endogenous elements (P, S, Fe, Cu and Zn) in individual human cells of three different types - Raji, Jurkat and Y79. Optimum conditions were obtained by using a sample introduction unit transporting cell suspension containing approx. 5 × 10⁴ cells per mL at a flow rate of 10 μL min^-1 to a nebulizer with narrow internal diameter (250 μm i.d.), mounted onto a total consumption spray chamber. Interference-free conditions were obtained in tandem MS mode (i) for P and S by pressurizing the collision/reaction cell (CRC) with O₂ and monitoring the PO⁺ and SO ⁺ reaction product ions and (ii) for Fe by pressurizing the CRC with NH₃ and monitoring the Fe(NH₃)₂⁺ reaction product ion. The quantification approach was validated by comparison of the absolute amounts of the target elements (in fg per cell) as obtained using SC-ICP-MS/MS with those obtained after acid digestion of approx. 2 × 10⁶ cells and subsequent solution ICP-MS/MS analysis ("bulk" analysis). A higher Pt cell content was observed upon increasing the concentration of the cisplatin solution the cells were exposed to during 24 h. The Pt mass per cell (fg) increased linearly as a function of the cisplatin concentration, but a higher Pt uptake was found in the case of Jurkat cells compared to the other cell types. A cell viability assay showed a lack of chemosensitivity to cisplatin below 200 μM for the Raji and Y79 cell line, but an IC₅₀ value of 11.1 ± 1.3 μM for Jurkat cells. This difference in chemo-responsiveness between the different cell types supported the difference in Pt uptake as indicated via SC-ICP-MS analysis. The increasing level of Pt did not have a marked effect on the contents of the endogenous elements monitored in Raji and Y79 cells, but a decrease in the P and S cell content upon increasing cisplatin treatment was observed for Jurkat cells. This can most likely be attributed to stress induced by the chemotherapeutic treatment in cells showing chemosensitivity towards cisplatin. The results also indicate differences in the absolute amount of endogenous element per cell between different cell types, suggesting the potential of SC-ICP-MS as a "metallo-fingerprinting" tool.

Recent development in Se-enriched yeast, lactic acid bacteria and bifidobacteria

Endemic selenium (Se) deficiency is a major worldwide nutritional challenge. Organic Se can be synthesized through physical and chemical methods that are conducive to human absorption, but its high production cost and low output cannot meet the actual demand for Se supplementation. Some microbes are known to convert inorganic Se into organic forms of high nutritional value and Se-enriched probiotics are the main representatives. The aim of the present review is to describe the characteristics of Se-enriched yeast, lactic acid bacteria, bifidobacteria and discuss their Se enrichment mechanisms. Se products metabolized by Se-enriched probiotics have been classified, such as Se nanoparticles (SeNPs) and selenoprotein, and their bioactivities have been assessed. The factors affecting the Se enrichment capacity of probiotics and their application in animal feed, food additives, and functional food production have been summarized. Moreover, a brief summary and the development of Se-enriched probiotics, particularly their potential applications in the field of biomedicine have been provided. In conclusion, Se-enriched probiotics not just have a wide range of applications in the food industry but also have great potential for application in the field of biomedicine in the future.

Compilation of selenium metabolite data in selenized yeasts

Selenium-enriched yeast has long been recognized as an important nutritional source of selenium and studies have suggested that supplementation with this material provides chemo-preventative benefits beyond those observed for selenomethionine supplementation, despite the fact that selenomethionine accounts for 60-84% of the total selenium in selenized yeasts. There is much ongoing research into the characterization of the species comprising the remaining 16-40% of the selenium, with nearly 100 unique selenium-containing metabolites identified in aqueous extracts of selenized yeasts (Saccharomyces cerevisiae). Herein, we discuss the analytical approaches involved in the identification and quantification of these metabolites, and present a recently created online database (DOI: 10.4224/40001921) of reported selenium species along with chemical structures and unique mass spectral features.

Analytical Methodologies for Agrometallomics: A Critical Review

Agrometallomics, as an independent interdiscipline, is first defined and described in this review. Metallic elements widely exist in agricultural plants, animals and edible fungi, seed, fertilizer, pesticide, feedstuff, as well as the agricultural environment and ecology, and even functional and pathogenic microorganisms. So, the agrometallome plays a vital role in molecular and organismic mechanisms like environmetallomics, metabolomics, proteomics, lipidomics, glycomics, immunomics, genomics, etc. To further reveal the inner and mutual mechanism of the agrometallome, comprehensive and systematic methodologies for the analysis of beneficial and toxic metals are indispensable to investigate elemental existence, concentration, distribution, speciation, and forms in agricultural lives and media. Based on agrometallomics, this review summarizes and discusses the advanced technical progress and future perspectives of metallic analytical approaches, which are categorized into ultrasensitive and high-throughput analysis, elemental speciation and state analysis, and spatial- and microanalysis. Furthermore, the progress of agrometallomic innovativeness greatly depends on the innovative development of modern metallic analysis approaches including, but not limited to, high sensitivity, elemental coverage, and anti-interference; high-resolution isotopic analysis; solid sampling and nondestructive analysis; metal chemical species and metal forms, associated molecular clusters, and macromolecular complexes analysis; and metal-related particles or metal within the microsize and even single cell or subcellular analysis.

Determination of elemental distribution and evaluation of elemental concentration in single Saccharomyces cerevisiae cells using single cell-inductively coupled plasma mass spectrometry

Single-cell analysis using inductively coupled plasma mass spectrometry (SC-ICP-MS) is a method to obtain qualitative and quantitative information of the elemental content and distribution of single cells. Six intrinsic target elements were analyzed in yeast cells at different cell growth phases cultured in medium with different phosphorus concentrations (0, 7, 14 mM) to study its effect on cell growth and composition. SC-ICP-MS results were compared with those obtained by the acid digestion and the average ratio was 0.81. The limits of detection of this method were 0.08, 2.54, 12.5, 0.02, 0.02, and 0.08 fg cell-1 for Mg, P, K, Mn, Cu, and Zn, respectively. During the exponential growth phase, the cells exhibited higher elemental contents, wider distribution for most elements, and larger cell size in comparison to the stationary growth phase. Phosphorus-free conditions reduced the average P content in single cells of stationary growth phase from 650 to 80 fg. Phosphorus deficiency led to decreasing intracellular concentrations not only of P but also of K and Cu, and to increasing Zn concentration after 48 h. Mg maintained its concentration at ∼0.11 fg µm-3 and did not change significantly under the three investigated conditions after 48 h. Accordingly, Mg content was successfully used to estimate the intracellular concentration of other intrinsic elements in single yeast cells. SC-ICP-MS is suited to determine target elements in single yeast cells, and allows the study of heterogeneity of cell composition and effects of stressors on the elemental content, distribution, and concentrations of intrinsic elements.

Mass spectrometry for multi-dimensional characterization of natural and synthetic materials at the nanoscale

Characterization of materials at the nanoscale plays a crucial role in in-depth understanding the nature and processes of the substances. Mass spectrometry (MS) has characterization capabilities for nanomaterials (NMs) and nanostructures by offering reliable multi-dimensional information consisting of accurate mass, isotopic, and molecular structural information. In the last decade, MS has emerged as a powerful nano-characterization technique. This review comprehensively summarizes the capabilities of MS in various aspects of nano-characterization that greatly enrich the toolbox of nano research. Compared with other characterization techniques, MS has unique capabilities for real-time monitoring and tracking reaction intermediates and by-products. Moreover, MS has shown application potential in some novel aspects, such as MS imaging of the biodistribution and fate of NMs in animals and humans, stable isotopic tracing of NMs, and risk assessment of NMs, which deserve update and integration into the current knowledge framework of nano-characterization.

Analysis of selenium nanoparticles in human plasma by capillary electrophoresis hyphenated to inductively coupled plasma mass spectrometry

Nanoparticles (NPs) are increasingly applied in research and development of new therapies. Characterization of NP systems most often include size, shape, size distribution, and charge but information on the chemical stability of NPs and investigation of the presence of dissolved species is most often missing in efficacy studies due to lack of appropriate methods. In this study, a method based on capillary electrophoresis coupled to inductively coupled plasma mass spectrometry (CE-ICP-MS) was established for analysis of selenium (Se) NPs and dissolved Se species in aqueous media. Peak area and migration time precisions (RSD) of 1.4-3.0% and 1.0-2.6%, respectively, were obtained. CE-ICP-MS analysis of a commercially available SeNP suspension (Q-SeNP) revealed large amounts of selenite corresponding to 32% of the total Se content in the suspension, indicating considerable NP degradation upon storage. The CE-ICP-MS method was modified using a coated fused silica capillary in order to analyze SeNPs in human plasma. Peak area and migration time precisions (RSD) in the range of 3.3-10.7% and 0.8-2.8%, respectively, were achieved. Degradation of polyvinyl alcohol (PVA)-coated SeNPs to selenite in human plasma was demonstrated using the modified method. The amounts of SeNP and selenite were estimated based on a correction factor for the ICP-MS signals of PVA-SeNP and dissolved Se. To the best of our knowledge, this is the first study of SeNPs by CE-ICP-MS and highlights the potential of CE-ICP-MS for quantitative characterization of the behavior of SeNPs in biological media.

Optimization of elemental selenium (Se(0)) determination in yeasts by anion-exchange HPLC-ICP-MS

An analytical method was developed for the speciation of elemental selenium (Se(0)) in selenized yeasts by anion-exchange HPLC-ICP-MS after its chemical transformation into SeSO₃^2- by reaction with sodium sulfite. The presence of Se(0) in the yeasts was further confirmed by single-particle ICP-MS. Indeed, Se nanoparticles, if present, are expected to be, at least partly, Se(0). X-ray photoelectron spectroscopy, a well-recognized technique for chemical element speciation in the solid state, was also used with this objective. Both methods were able to confirm the presence of Se(0) in the selenized yeasts but failed to provide reliable quantitative results. Analytical performances of the HPLC-ICP-MS method were then evaluated for Se(0) determination. Quantification limits of 1 mg/kg were reached. The recovery levels from an added quantity comprised between 93 and 101%. Within-run and between-run precisions were both below 8%. The procedure developed was finally applied to quantify Se(0) content in a series of seven yeast batches from different suppliers. Se(0) was found to be present in all the studied yeasts and represented on average 10-15% of the total Se.

Efficiency and stability evaluation of Cu2O/MWCNTs filters for virus removal from water

Both multi-walled carbon nanotubes (MWCNTs) and metal or metal oxides have demonstrated virus removal efficacy in drinking water applications. In this study, MWCNTs were coated with copper(I) oxide (Cu₂O) using three distinct synthesis procedures (copper ion attachment, copper hydroxide precipitation, and [Cu(NH₃)₄]²⁺ complex attachment) and virus removal efficacy (using MS2 bacteriophages) was evaluated. All synthesis procedures resulted in the presence of adsorbed, nanosized Cu₂O particles on the MWCNTs, shown using X-ray diffraction. Further, transmission electron microscopy confirmed uniform copper(I) oxide distribution along the MWCNTs for all three materials. Virus removal efficacy was assessed for all three synthesised composites both before and after material conditioning (filtering for at least 24 h/280 mL/h), and accounting for additional MS2 inactivation in the permeate due to continued copper inactivation from dissolved/desorbed copper in permeate (time-control). Material conditioning influenced virus removal, with the first litres of water containing higher concentrations of copper than the sixth litres of water, suggesting excess or non-bonded copper species dissolve from filters. Higher copper dissolution was observed for water at pH 5 than at pH 7, which decreased with time. Copper dissolution most likely caused an associated decrease in copper adsorbed to MWCNTs in the filters, which may explain the observed lower MS2 removal efficacy after conditioning. Additionally, the time-control study (immediately after filtration as compared to 2 h after filtration) highlighted continued MS2 inactivation in the permeate over time. The obtained results indicate that the synthesis procedure influences virus removal efficacy for MWCNTs coated with copper oxides and that virus removal is likely due to not only virus electrostatic adsorption to the coated MWCNTs, but also through antiviral properties of copper which continues to act in the permeate. In conclusion, it is highly important to revise the methods of testing filter materials for virus removal, as well as procedure for virus concentration evaluation.