Capillary electrophoresis/inductively-coupled plasma-mass spectrometry: development and optimization of a high resolution analytical tool for the size-based characterization of nanomaterials in dietary supplements

Quantitative separation of polystyrene nanoparticles in environmental matrices with picogram detection limits using capillary electrophoresis

We developed a capillary electrophoresis method to separate polystyrene particles (PSPs) with different sizes or different surface functionalities. Separations were performed in buffer and 100 mg L-1 clay or 100 mg L-1 Suwanee River humic acid. In all solutions, PSPs were baseline or near-baseline resolved in less than 15 minutes.

Conjugation monitoring of gold nanoparticles with alkanedithiols by capillary zone electrophoresis

Alkanedithiols were used for the conjugation of gold nanoparticles (AuNP) prepared by a solution plasma process. Capillary zone electrophoresis was utilized for the monitoring of the conjugated AuNP. When 1,6-hexanedithiol (HDT) was used as a linker, a resolved peak from the AuNP was detected in the electropherogram; the resolved peak was attributed to the conjugated AuNP. The resolved peak was developed with increasing concentrations of HDT, while the peak of the AuNP decreased complementary. The resolved peak also tended to develop along with the standing time at least up to 7 weeks. The electrophoretic mobility of the conjugated AuNP was almost identical over the HDT concentrations examined, suggesting that the conjugation of the AuNP did not proceed further, such as aggregate/agglomerate formation. The conjugation monitoring was also examined with some dithiols and monothiols. Resolved peak of the conjugated AuNP was also detected with 1,2-ethanedithiol and 2-aminoethanethiol.

Development of Two-Dimensional Offline Coupling of Asymmetrical Flow Field-Flow Fractionation and Capillary Electrophoresis for the Separation of a Five-Component Submicrometer Particle Mixture

Submicrometer colloidal particles are widely applied in a variety of industrial products. While precise size and surface charge control is crucial to the stability and functionality of these materials, a tool to determine these properties with sufficient resolution, detection sensitivity, and robustness is still not available. The recently reported offline coupling of asymmetrical flow field-flow fractionation and capillary electrophoresis (AF4 × CE) shows success in improving the separation resolution for nanoparticles; however, challenges remain for sensitive multiple-component submicrometer particle analysis because of wide size and mobility distributions. We here report offline coupling of an AF4 method and a CE method, which utilized the online reversed electrode polarity stacking mode, to successfully characterize a five-component, submicrometer particle mixture. The mixture was successfully separated and detected with an improved inter- and intracomponent resolution. Therefore, our developed platform holds great potential for industrial applications involving multiple-component particle mixtures.

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.

Quantitative Detection of Zinc Oxide Nanoparticle in Environmental Water by Cloud Point Extraction Combined ICP-MS

The increasing usage of zinc oxide nanoparticles (ZnONPs) inevitably leads to their release into the environment. To understand their fate and toxicity in water systems, a reliable method for the quantitative analysis of ZnONPs in environmental waters is urgently needed to be established. In this study, a quantitative analytical method of ZnONPs in environmental waters was developed by cloud point extraction (CPE) combined inductively coupled plasma mass spectrometry (ICP-MS). To obtain high recoveries of ZnONPs, the CPE parameters including pH, surfactant concentration, salt concentration, bath temperature, and time were optimized. The results demonstrated that the addition of β-mercaptoethylamine could significantly reduce the interference of Zn2+ on the extraction of ZnONPs, while the CPE approach was not affected significantly by the typical environmental inorganic ion and ENMs (such as Au, TiO2, and Al2O3). The extraction method of ZnONPs with different diameters was also assessed, and satisfactory extraction efficiency was obtained. The results of ZnONP concentration in collected environmental water were in the range of $0.2\pm 0.009$ - $8.2\pm 1.8$  μg/L. And the recoveries of ZnONPs in different environmental waters were $62.2\pm 2.0$ - $88.1\pm 9.6\%$ at low concentration spiked levels (12.57-54.68 μg/L), demonstrating that it is efficient to extract trace ZnONPs from real environmental waters. This established method offered a reliable method for the quantitative determination of ZnONPs in environmental waters, which could further promote the study of the environmental behavior, fate, and toxicity of ZnONPs in an aqueous environment.

Intracellular silver speciation by coupling capillary electrophoresis to ICP-MS integrating a high performance spiral flow spray chamber

The study of silver species and their distribution/transformation in cell interior is of high significance for the elucidation of toxicology of silver nanoparticles (AgNPs). The intracellular speciation of dissolved Ag(I) and AgNPs was reported. The analytical platform integrated capillary electrophoresis (CE) to inductively coupled plasma-mass spectrometry (ICP-MS) incorporating a high efficiency interface and a high performance spiral flow spray chamber (SFSC). The interface and the SFSC provide a favorable detection limit of 87 ng L^-1 for the dissolved Ag(I). Total silver content was quantified by ICP-MS subject to digestion of the cell lysate, and quantification of AgNPs was carried out by subtraction. The speciation of dissolved Ag(I) and AgNPs in culture medium and HepG2 cells was performed, with RSDs of <3% for relative peak area and <2% for migration time, as well as spiking recoveries of 93.8%-94.3% in opti-MEM and 92.7%-106.6% in cell lysate. The present study indicated higher solubility of AgNPs in the cell interior with respect to that in the culture medium, due to oxidative stress or acidic microenvironment in the cancer cells.

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.

Incidence of metal-based nanoparticles in the conventional wastewater treatment process

Metal-based nanoparticles (NPs) can be found in wastewater streams, which are significant pathways for the release of NPs to the environment. Determination of the NPs concentration in wastewater streams is important for performing appropriate ecotoxicological evaluations. The aim of this work was to determine the incidence of NPs from 13 different elements throughout the wastewater treatment process by using single particle inductively coupled plasma mass spectrometry (spICP-MS). The incidence was determined in samples of the influent, post-primary treatment and effluent of the activated sludge process, as well as in the reclaimed water of a full-scale wastewater treatment plant (WWTP). In addition, concentration of NPs was determined in the waste activated sludge and in the anaerobic digester. The concentration of metal-based NPs in the influent wastewater were between 1,600 and 10,700 ng/L for elements such as Ti, Fe, Ce, Mg, Zn and Cu, while that for Ni, Al, Ag, Au, Co and Cd was below 100 ng/L. Concentrations in reclaimed water ranged between 0.6 and 721 ng/L, ranked as Mg > Ti > Fe > Cu > Ni > Ce > Zn > Mn > Al  > Co > Ag > Cd  > Au. Results indicated that the activated sludge process and reclaimed water system removed 84-99% of natural and engineered metal-based NPs from influent to reclaimed water, except for Mg, Ni and Cd where the removal ranged from 70 to 78%. The highest concentrations of NPs were found in the waste activated sludge and anaerobic sludge, ranging from 0.5 to 39,900 ng/L. The size distribution of NPs differed in different wastewater streams within the WWTP, resulting in smaller particles in the effluent (20-180 nm) than in the influent (23-233 nm) for most elements. Conversely, NPs were notably larger in the waste activated sludge samples than in the anaerobic sludge or wastewater, since conditions in the secondary treatment lead to precipitation of several metal-based NPs. The incidence of metal-based NPs from 13 elements in wastewater decreased significatively after the conventional wastewater treatment train. However, anaerobic digesters store high NPs concentrations. Hence, the disposal of sludge needs to take this into account to evaluate the risk of the release of NPs to the environment.

Contributions of Capillary Electrophoresis in Analytical Nanometrology: A Critical View

An overview on the increasing role of capillary electrophoresis in characterization and direct analysis of nanomaterials is herein presented. The niche of electrophoretic approaches in nanometrology is so relevant that nonmetallic, metal, metal oxide nanoparticles, and quantum dots have been analyzed to be targeted via capillary electrophoresis with conventional detection systems or coupling arrangements aimed at increasing selectivity and sensitivity toward either pristine or conjugated nanoparticles. Moreover, parameters altering intrinsic properties of nanoparticles may be optimized to gather the desired results and identify nanomaterials according to their size, shape, or associations with binding agents. The usefulness and quickness of capillary electrophoresis for quantifying or screening ultrasmall-sized particles enables this technique to set an example for analysis of standards or previously synthesized nanostructures in research or routine laboratories. Abundant evidence of the suitability of electrophoretic approaches for characterization and direct determination of nanomaterials in actual samples has been provided in this review, together with a discussion about hyphenation with state-of-the art detectors and comparison between capillary electrophoresis with other separation approaches. This permits scientific community to be optimistic in the short term.

Unravelling neurological disorders through metallomics-based approaches

Understanding the biological process involving metals and biomolecules in the brain is essential for establishing the origin of neurological disorders, such as neurodegenerative and psychiatric diseases. From this perspective, this critical review presents recent advances in this topic, showing possible mechanisms involving the disruption of metal homeostasis and the pathogenesis of neurological disorders. We also discuss the main challenges observed in metallomics studies associated with neurological disorders, including those related to sample preparation and analyte quantification.

Understanding the relationship between viral infections and trace elements from a metallomics perspective: implications for COVID-19

Recently, the World Health Organization (WHO) declared a pandemic situation due to a new viral infection (COVID-19) caused by a novel virus (Sars-CoV-2). COVID-19 is today the leading cause of death from viral infections in the world. It is known that many elements play important roles in viral infections, both in virus survival, and in the activation of the host's immune system, which depends on the presence of micronutrients to maintain the integrity of its functions. In this sense, the metallome can be an important object of study for understanding viral infections. Therefore, this work presents an overview of the role of trace elements in the immune system and the state of the art in metallomics, highlighting the challenges found in studies focusing on viral infections.

Separation of polystyrene nanoparticles bearing different carboxyl group densities and functional groups quantification with capillary electrophoresis and asymmetrical flow field flow fractionation

Two sets of polystyrene nanoparticles (PSNPs) with comparable core sizes but different carboxyl group densities were made and separated using asymmetric flow field flow fractionation (AF4), capillary electrophoresis (CE), and the off-line hyphenation of both methods. Our results revealed the significant potential of two-dimensional off-line AF4-CE hyphenation to improve the separation and demonstrated for the first time, the applicability of CE to determine the functional group density of nanoparticles (NPs). Compared to the result acquired with conductometric titration, the result obtained with synthesized 100 nm sized PSNPs revealed only a slight deviation of 1.7%. Commercial 100 nm sized PSNPs yielded a deviation of 4.6%. For 60 nm sized PSNPs, a larger deviation of 10.6% between both methods was observed, which is attributed to the lower separation resolution.

High separation efficiency of gold nanomaterials of different aspect ratio and size using capillary transient isotachophoresis

Two modes of capillary electrophoresis (CE), capillary zone electrophoresis (CZE) and capillary transient isotachophoresis (ctITP), were compared for the detection and separation of spherical gold nanoparticles (AuNPs) and gold nanorods (AuNRs). The development of ctITP using two different leading ions is described. Overall, when compared to traditional capillary zone electrophoresis (CZE), ctITP resulted in improved peak shape and peak efficiency. Specifically, the number of theoretical plates for AuNR samples increased by a factor of 2-2.5 depending on the choice of leading ion. Further, using ctITP two AuNRs differing by aspect ratio were baseline resolved, whereas the same AuNRs could not be separated using CZE or other techniques like single particle inductively coupled plasma mass spectrometry (spICP-MS) and asymmetric flow field-flow fractionation (AF4). The results of this study demonstrate that ctITP is an efficient on-line technique for the improved detection and separation of gold nanomaterials in CE.

Separation of polystyrene nanoparticles with different coatings using two-dimensional off-line coupling of asymmetrical flow field flow fractionation and capillary electrophoresis

The successful off-line coupling of asymmetrical flow field flow fractionation (AF4) and capillary electrophoresis (CE) for separation of nanoparticles (NPs) with different surface coatings was shown. We could successfully demonstrate that, in a certain NP size range, hyphenation of both techniques significantly improved the separation of differently coated NPs. Three mixtures of polystyrene nanoparticles (PS-NPs) with comparable core sizes but different coatings (no coating/carboxyl-coated) were studied. Separation in either method resulted in non-baseline resolved or non-separated peaks. In contrast, two-dimensional off-line coupling of AF4 and CE resulted in clearly separated regions in their 2 D plots in case of 20 and 50 nm particle mixtures, whereas the 100 nm NP mixture could not be separated at all. Various factors affecting the separation like hydrodynamic diameter or SDS concentration were discussed.

Analytical strategy based on asymmetric flow field flow fractionation hyphenated to ICP-MS and complementary techniques to study gold nanoparticles transformations in cell culture medium

An analytical methodology based on asymmetric flow field flow fractionation (AF4) hyphenated to inductively coupled plasma mass spectrometry (ICP-MS) has been developed to study gold nanoparticles (AuNPs) in cell culture medium (Dulbecco's Modified Eagle Medium, DMEM, containing 10% fetal bovine serum, FBS, and antibiotics) used for in vitro toxicological studies. AF4-ICP-MS separation of AuNPs was performed using a regenerated cellulose membrane (molecular weight cut-off, MWCO, of 10 kDa). The carrier composition and the AF4 separation program were optimized. Under the optimum conditions, AuNPs of different types, i.e. phosphate buffered saline (PBS) and citrate stabilized, and sizes (10, 30 and 40 nm), without and with cell culture medium could be separated. The developed method allowed to detect transformations in AuNPs and dissolved gold species (Au³⁺) induced by this medium, such as an increase in the hydrodynamic volume and oxidation. Centrifugal ultrafiltration (CU), transmission electron microscopy (TEM) and Ultraviolet-visible (UV-vis) absorption spectrophotometry have been used as complementary techniques to study these processes. This information is of major interest to have a correct interpretation of the in vitro toxicological studies of NPs, which are more and more demanded due to the increasing concerns about the safe use of these materials and their impacts. This work demonstrates the potential of hyphenated techniques based on AF4 to achieve this relevant information.

Detection of contaminants in water supply: A review on state-of-the-art monitoring technologies and their applications

Water monitoring technologies are widely used for contaminants detection in wide variety of water ecology applications such as water treatment plant and water distribution system. A tremendous amount of research has been conducted over the past decades to develop robust and efficient techniques of contaminants detection with minimum operating cost and energy. Recent developments in spectroscopic techniques and biosensor approach have improved the detection sensitivities, quantitatively and qualitatively. The availability of in-situ measurements and multiple detection analyses has expanded the water monitoring applications in various advanced techniques including successful establishment in hand-held sensing devices which improves portability in real-time basis for the detection of contaminant, such as microorganisms, pesticides, heavy metal ions, inorganic and organic components. This paper intends to review the developments in water quality monitoring technologies for the detection of biological and chemical contaminants in accordance with instrumental limitations. Particularly, this review focuses on the most recently developed techniques for water contaminant detection applications. Several recommendations and prospective views on the developments in water quality assessments will also be included.

Short-chained oligo(ethylene oxide)-functionalized gold nanoparticles: realization of significant protein resistance

Protein corona formed on nanomaterial surfaces play an important role in the bioavailability and cellular uptake of nanomaterials. Modification of surfaces with oligoethylene glycols (OEG) are a common way to improve the resistivity of nanomaterials to protein adsorption. Short-chain ethylene oxide (EO) oligomers have been shown to improve the protein resistance of planar Au surfaces. We describe the application of these EO oligomers for improved protein resistance of 30 nm spherical gold nanoparticles (AuNPs). Functionalized AuNPs were characterized using UV-Vis spectroscopy, dynamic light scattering (DLS), and zeta potential measurements. Capillary electrophoresis (CE) was used for separation and quantitation of AuNPs and AuNP-protein mixtures. Specifically, nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) was employed for the determination of equilibrium and rate constants for binding between citrate-stabilized AuNPs and two model proteins, lysozyme and fibrinogen. Semi-quantitative CE analysis was carried out for mixtures of EO-functionalized AuNPs and proteins, and results demonstrated a 2.5-fold to 10-fold increase in protein binding resistance to lysozyme depending on the AuNP surface functionalization and a 15-fold increase in protein binding resistance to fibrinogen for both EO oligomers examined in this study. Graphical abstract Using capillary electrophoresis, the addition of short-chained oligo(ethylene oxide) ligands to gold nanoparticles was shown to improve protein binding resistance up to 15-fold.

Nanomaterials in Food Products: A New Analytical Challenge

This chapter focuses on the problem of detecting, characterizing, and determining the concentration of nanomaterials in foods and other biological matrices. After providing an overview of the unique challenges associated with nanoparticle metrology in complex media, sample pretreatment methods (including extraction, digestion, and inline chromatographic separation), imaging analysis, and nanomaterial quantification methods are presented in detail. The chapter also addresses numerous methods under development, including atmospheric scanning electron microscopy, single-particle inductively coupled plasma mass spectrometry, immunological detection methods, and optical techniques such surface plasmon resonance. The chapter concludes with an overview of the research needs in this area.

Analysis of silver and gold nanoparticles in environmental water using single particle-inductively coupled plasma-mass spectrometry

The production and use of engineering nanomaterials (ENMs) leads to the release of manufactured or engineered nanoparticles into environment. The quantification and characterization of ENMs are crucial for the assessment of their environmental fate, transport behavior and health risks to humans. To analyze the size distribution and particle number concentration of AgNPs and AuNPs in environmental water and track their stability at low number concentration, a systematic study on SP-ICPMS was presented. The Poisson statistics was used to discuss the effect of dwell time and particle number concentration theoretically on the detection of NPs in solution by SP-ICPMS. The dynamic range of SP-ICPMS is approximately two orders of magnitude. The size detection limits for silver and gold nanoparticle in ultrapure water are 20 and 19nm respectively. The detection limit of nanoparticle number concentration is 8×10(4)particlesL(-1). Size distribution of commercial silver and gold nanoparticle dispersions is determined by SP-ICP-MS, which was in accordance with the TEM results. High particle concentration recoveries of spiked AgNPs and AuNPs are obtained (80-108% and 85-107% for AgNPs and AuNPs respectively in ultrapure and filtered natural water). It indicates that SP-ICPMS can be used to detect AgNPs and AuNPs. The filtration study with different membranes showed that filtration might be a problematic pre-treatment method for the detection of AgNPs and AuNPs in environmental water. Furthermore, the stability of citrate-coated AgNPs and tannic acid-coated AuNPs spiked into filtrated natural and waste water matrix was also studied at low concentration using SP-ICP-MS measurements. Dissolution of AgNPs was observed while AuNPs was stable during a ten day incubation period. Finally SP-ICPMS was used to analyze NPs in natural water and waste water. The results indicate that SP-ICPMS can be used to size metallic nanoparticles sensitively of low concentration under realistic environmental conditions.

Speciation of metal-based nanomaterials in human serum characterized by capillary electrophoresis coupled to ICP-MS: a case study of gold nanoparticles

The development and optimization of a versatile analytical system for the speciation analysis of metal-containing nanoscale materials in blood serum is reported herein. Based on capillary electrophoresis (CE) interfaced with inductively coupled plasma mass spectrometry (ICP-MS), the method was shown to be feasible to investigate the interactions between serum proteins and gold nanoparticles of potential medicinal use, which are their first and foremost occurrence upon their entry into the circulatory system. To improve the separation resolution between the intact nanoparticles and different protein conjugates, the CE system was optimized with an emphasis on compatibility with physiological conditions, avoiding aggregation effects, and analyte recovery. Optimization allowed also for acquiring the acceptable figures of merit such as migration time and peak area precision of 1.0-6.4% and 2.4-6.9%, respectively, detection limits in the range of 0.8-1.0 μg L(-1) Au, and capillary recoveries on the order of 86-97%, depending on the nanoparticle size and conjugate type. We sytematically investigated the role of size in mediating protein adsorption to gold nanoparticles in a real-serum environment. At the initial stage of surface coating, the speciation of smaller particles (5 and 10 nm) was found to be dominated by albumin, transferrin (both in apo- and holo-form) playing the secondary role in developing the protein corona. For 20 and 50 nm nanoparticles, the contribution of transferrin is initially comparable; however, with time it becomes replaced by albumin. The time of attaining equilibrium adsorption is also a function of particle size but for the whole size range investigated, albumin is the only equilibrium binding partner. These principal findings prove that for metal-based nanomaterials in general, serum protein conjugates could be variable in composition depending on the protein abundance and binding affinity, as well as the residence time in the bloodstream.

Capillary electrophoresis coupled with inductively coupled mass spectrometry as an alternative to cloud point extraction based methods for rapid quantification of silver ions and surface coated silver nanoparticles

Speciation and accurate quantification of ionic silver and metallic silver nanoparticles are critical to investigate silver toxicity and to determine the shelf-life of products that contain nano silver under various storage conditions. We developed a rapid method for quantification of silver ions and silver nanoparticles using capillary electrophoresis (CE) interfaced with inductively-coupled plasma mass spectrometry (ICPMS). The addition of 2-mercaptopropionylglycine (tiopronin) to the background electrolyte was used to facilitate the chromatographic separation of ionic silver and maintain the oxidation state of silver. The obtained limits of detection were 0.05 μg kg(-1) of silver nanoparticles and 0.03 μg kg(-1) of ionic silver. Nanoparticles of varied sizes (10-110 nm) with different surface coating, including citrate acid, lipoic acid, polyvinylpyrrolidone and bovine serum albumin (BSA) were successfully analyzed. Particularly good recoveries (>93%) were obtained for both ionic silver and silver nanoparticle in the presence of excess amount of BSA. The method was further tested with six commercially available dietary supplements which varied in concentration and matrix components. The summed values of silver ions and silver nanoparticles correlated well with the total silver concentration determined by ICPMS after acid digestion. This method can serve as an alternative to cloud point extraction technique when the extraction efficiency for protein coated nanoparticles is low.