Comparison of sp-ICP-MS and MDG-ICP-MS for the determination of particle number concentration

Analytical chemistry of engineered nanomaterials: Part 1. Scope, regulation, legislation, and metrology (IUPAC Technical Report)

Analytical chemistry is crucial for understanding the complex behavior observed for engineered nanomaterials (ENMs). A variety of analytical chemistry techniques and methodological approaches are used for isolation/purification and determination of the composition of pristine nanomaterials and for the detection, identification, and quantification of nanomaterials in nano-enabled consumer products and the complex matrices found in cosmetics, food, and environmental and biological samples. Adequate characterization of ENMs also requires physicochemical characterization of number of other properties, including size, shape, and structure. The requirement for assessment of a number of ENM properties frequently requires interdisciplinary approaches and multi-modal analysis methods. This technical report starts with an overview of ENMs definitions and classification, their properties, and analytical scenarios encountered with the analysis of both pristine nanomaterials and complex matrices containing different nanomaterials. An evaluation of the current status regarding nanomaterial identification and characterization for regulatory purposes and legislation, including emerging regulations and related scientific opinions, is provided. The technical report also presents a large and critical overview of the metrology of nanomaterials, including available reference materials and the development and validation of standardized methods that are currently available to address characterization and analysis challenges. The report focuses mainly on chemical analysis techniques and thus it is complementary to previous IUPAC technical reports focused on characterizing the physical parameters of ENMs and on nanotoxicology.

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.

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.

Recent trends in analysis of nanoparticles in biological matrices

The need to assess the human and environmental risks of nanoparticles (NPs) has prompted an adaptation of existing techniques and the development of new ones. Nanoparticle analysis poses a great challenge as the analytical information has to consider both physical (e.g. size and shape) and chemical (e.g. elemental composition) state of the analyte. Furthermore, one has to contemplate the transformation of NPs during the sample preparation and provide sufficient information about the new species derived from such alteration. Traditional techniques commonly used for NP analysis such as microscopy and light scattering are still frequently used for NPs in simple matrices; however, they have limitations in the analysis of complex environmental and biological samples. On the other hand, recent improvements in data acquisition frequencies and reduction of settling time of ICP-MS brought inorganic mass spectrometry into the forefront of NPs analysis. However, with the increasing demand of analytical information related to NPs, emerging techniques such as enhanced darkfield hyperspectral imaging, nano-SIMS and mass cytometry are in their way to fill the gaps. This trend review presents and discusses the state-of-the-art analytical techniques and sample preparation methods for NP analysis in biological matrices. Graphical abstract ᅟ.

Validation of Single Particle ICP-MS for Routine Measurements of Nanoparticle Size and Number Size Distribution

Single particle inductively coupled plasma-mass spectrometry (spICP-MS) is an emerging technique capable of simultaneously measuring nanoparticle size and number concentration of metal-containing nanoparticles (NPs) at environmental levels. single particle ICP-MS will become an established measurement method once the metrological quality of the measurement results it produces have been proven incontrovertibly. This Article presents the first validation of spICP-MS capabilities for measuring mean NP size and number size distribution of gold nanoparticles (AuNPs). The validation is achieved by (i) calibration based on the consensus value for particle size derived from six different sizing techniques applied to National Institute of Standards and Technology (NIST) Reference Material (RM) 8013; (ii) comparison with high-resolution scanning electron microscopy (HR-SEM) used as a reference method, which is linked to the International System of Units (SI) through a calibration standard characterized by the NIST metrological atomic force microscope; and (iii) evaluation of the uncertainty associated with the measurement of the mean particle size to enable comparison of the spICP-MS and HR-SEM methods. After establishing HR-SEM and spICP-MS measurement protocols, both methods were used to characterize commercial AuNP suspensions of three different sizes (30, 60, and 100 nm) with four different coatings and surface charge at pH 7. Single particle ICP-MS measurements (corroborated by HR-SEM) revealed the existence of two distinct subpopulations of particles in the number size distributions for four of the 60 nm commercial suspensions, a fact that was not apparent in the measurement results supplied by the vendor using transmission electron microscopy. This finding illustrates the utility of spICP-MS for routine characterization of commercial AuNP suspensions regardless of size or coating.

Metal Stable Isotope Tagging: Renaissance of Radioimmunoassay for Multiplex and Absolute Quantification of Biomolecules

The unambiguous quantification of biomolecules is of great significance in fundamental biological research as well as practical clinical diagnosis. Due to the lack of a detectable moiety, the direct and highly sensitive quantification of biomolecules is often a "mission impossible". Consequently, tagging strategies to introduce detectable moieties for labeling target biomolecules were invented, which had a long and significant impact on studies of biomolecules in the past decades. For instance, immunoassays have been developed with radioisotope tagging by Yalow and Berson in the late 1950s. The later languishment of this technology can be almost exclusively ascribed to the use of radioactive isotopes, which led to the development of nonradioactive tagging strategy-based assays such as enzyme-linked immunosorbent assay, fluorescent immunoassay, and chemiluminescent and electrochemiluminescent immunoassay. Despite great success, these strategies suffered from drawbacks such as limited spectral window capacity for multiplex detection and inability to provide absolute quantification of biomolecules. After recalling the sequences of tagging strategies, an apparent question is why not use stable isotopes from the start? A reasonable explanation is the lack of reliable means for accurate and precise quantification of stable isotopes at that time. The situation has changed greatly at present, since several atomic mass spectrometric measures for metal stable isotopes have been developed. Among the newly developed techniques, inductively coupled plasma mass spectrometry is an ideal technique to determine metal stable isotope-tagged biomolecules, for its high sensitivity, wide dynamic linear range, and more importantly multiplex and absolute quantification ability. Since the first published report by our group, metal stable isotope tagging has become a revolutionary technique and gained great success in biomolecule quantification. An exciting research highlight in this area is the development and application of the mass cytometer, which fully exploited the multiplexing potential of metal stable isotope tagging. It realized the simultaneous detection of dozens of parameters in single cells, accurate immunophenotyping in cell populations, through modeling of intracellular signaling network and undoubted discrimination of function and connection of cell subsets. Metal stable isotope tagging has great potential applications in hematopoiesis, immunology, stem cells, cancer, and drug screening related research and opened a post-fluorescence era of cytometry. Herein, we review the development of biomolecule quantification using metal stable isotope tagging. Particularly, the power of multiplex and absolute quantification is demonstrated. We address the advantages, applicable situations, and limitations of metal stable isotope tagging strategies and propose suggestions for future developments. The transfer of enzymatic or fluorescent tagging to metal stable isotope tagging may occur in many aspects of biological and clinical practices in the near future, just as the revolution from radioactive isotope tagging to fluorescent tagging happened in the past.