Chemische Charakterisierung und Spurenanalytik
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In the last decades, significant efforts have been made to investigate possible cytotoxic effects of metallic nanoparticles (NPs). Methodologies enabling precise information regarding uptake and intracellular distribution of NPs at the single cell level remain to be established. Mass cytometry (MC) has been developed for high-dimensional single cell analyses and is a promising tool to quantify NP−cell interactions. Here, we aim to establish a new MC-based quantification procedure to receive absolute numbers of NPs per single cell by using a calibration that considers the specific transmission efficiency (TE) of suspended NPs. The current MC-quantification strategy accept TE values of complementary metal solutions. In this study, we demonstrate the different transmission behavior of 50 nm silver NPs (AgNP) and silver nitrate solution. We have used identical AgNPs for calibration as for in vitro-differentiated macrophages (THP-1 cell line) in a time- and dose-dependent manner. Our quantification relies on silver intensities measuring AgNPs in the same detection mode as the cells. Results were comparable with the TE quantification strategy using AgNPs but differed when using ionic silver. Furthermore, intact and digested cell aliquots were measured to investigate the impact of MC sample processing on the amount of AgNPs/cell. Taken together, we have provided a MC-specific calibration procedure to precisely calculate absolute numbers of NPs per single cell. Combined with its unique feature of multiplexing up to 50 parameters, MC provides much more information on the single cell level than single cell-inductively coupled plasma mass spectrometry (SC-ICP-MS) and, therefore, offers new opportunities in nanotoxicology.
Inductively coupled plasma-mass spectrometry (ICP-MS) is a well-established analytical method offering high sensitivity and multi-element analysis. ICP-MS has found acceptance in various application areas ranging from material analysis to applications in the life sciences. Within the last 15 years new strategies for the sensitive detection and accurate quantification of biomolecules in complex biomedical samples have been developed. Recent instrumental improvements have contributed to this progress.
As most of the biomolecules do not contain endogenous metals etectable with ICP-MS, bioconjugation with artificial metal-containing tags based on metal-loaded chelate complexes or nanoparticles is increasingly applied to determine biomolecules indirectly. Especially, the combination of immunohistochemical workflows using lanthanoid-tagged antibodies and ICP-MS detection provides new insights in the complexity and interdependency of cellular processes. Single-cell ICP-MS, also termed as mass cytometry, allows high-dimensional analysis of biomarkers in cell populations at single-cell resolution. For that purpose, lanthanoid isotope labelled antibodies are used to detect their corresponding target molecules. The visualisation of the elemental distribution is possible with laser ablation ICP-MS (LA-ICPMS) at high spatial resolution. Especially, the combination of LA with ICP time-of-flight mass spectrometry, also referred to as imaging mass cytometry (IMC), opens new possibilities for multiparametric tissue imaging at the single-cell level and even below. The lanthanoid localisation and concentration can be linked to their conjugated antibody target providing valuable information about surface markers, intracellular signalling molecules to measure biological function, and the network state of an individual cell in a tissue.
This book chapter focuses on new applications, where the multi-element capabilities of ICP-MS are used for the detection of lanthanoids applied as artificial elemental stains or tags for biomolecules and in particular antibodies.
Silver nanoparticles (AgNPs), have a high scientific and commercial impact due to their important antibacterial properties. However, there are serious concerns about their toxicological adverse effects as a consequence of their broad range of applications. Particularly, the impact of AgNPs on cells is not very well understood yet and there is a current demand to develop analytical methodologies providing information about the interaction and distribution of AgNPs at a single cell level. In this research, mass cytometry was used to introduce a new quantitative approach to study the uptake of AgNPs by individual THP-1 macrophages as a cell model system. Here, we show that this methodology provides not only multi-variate phenotypic information of individual cells but enables the quantitative analysis of AgNPs associated to cells in a single measurement by performing an external calibration using AgNPs suspension. Using differentiated THP-1 cells, we monitored and quantified the uptake of 50 nm AgNPs in a time and dose-dependent manner by mass cytometry. 7 to 120 AgNPs per cell (2 to 89 fg Ag/cell) were determined after exposure of differentiated THP-1 cells to low AgNPs concentrations of 0.1 and 1.0 mg L-1, at time points of 4 and 24 h. The results were validated by mass cytometric analysis of digested cells working as a conventional inductively coupled plasma mass spectrometry, ICP-MS. This study demonstrates the power of single cell analysis by mass cytometry even for low doses experiments as a new analytical tool for hitherto unaddressed questions in nanotoxicology.