Time-resolved ICP-MS analysis of mineral element contents and distribution patterns in single cells

Single-Cell Analysis of Elemental Contents by Laser Ablation-Inductively Coupled Plasma Mass Spectrometry

Elemental analysis at the single-cell level is an emerging technique in the field of inductively coupled plasma mass spectrometry (ICP-MS). In comparison to the analysis of cell suspensions by fast time-resolved analysis, single-cell sampling by laser ablation (LA) allows the discriminatory analysis of single cells according to their size and morphology. In this study, we evaluated the changes in elemental contents in a single cell through differentiation of rat adrenal pheochromocytoma into neuron-like cells by LA-ICP-MS. The contents of seven essential minerals were increased about 2-3 times after the differentiation. In addition, we evaluated the degree of differentiation at the single-cell level by means of imaging cytometry after immunofluorescence staining of microtubule-associated protein 2 (Map2), a neuron-specific protein. The fluorescence intensities of Alexa Fluor 488-conjugated secondary antibody against the anti-Map2 primary antibody showed large variations among the cells after the onset of differentiation. Although the average fluorescence intensity was increased through the differentiation, there were still less-matured neuron-like cells that exhibited a lower fluorescence intensity after 5 days of differentiation. Since a positive correlation between the fluorescence intensity and the cell size in area was found, we separately measured the elemental contents in the less-matured smaller cells and well-matured larger cells by LA-ICP-MS. The larger cells had higher elemental contents than the smaller cells, indicating that the essential minerals are highly required at a later stage of differentiation.

Determination of carbon in microplastics and single cells by total consumption microdroplet ICP-TOFMS

Recently, spICP-MS analyses of microplastics have demonstrated that the detection capabilities of ICP-MS are sufficient to determine the size and composition of such materials. However, solution nebulization or microdroplet generation limits the sizes of droplets, microparticles, or cells that can be efficiently introduced into commonly used horizontal ICP-MS configurations. Therefore, we introduced the development of a downward-pointing ICP coupled to a time-of-flight mass spectrometer (ICP-TOFMS), which enables quantitative transport of large microdroplets (diameters up to 90 µm) into the ICP. Here, we report the capabilities of downward ICP-TOFMS for the quantitative analysis of single cells and microplastic particles. For calibration of element mass amount per particle or cell, microdroplets (70 µm diameter) composed of multielement solutions were measured by ICP-TOFMS. Microplastic beads (polystyrene) and spleenocyte cells were then also embedded in microdroplets and measured by ICP-TOFMS with ion optics optimized to determine the signals from 12C+ and other isotopes of interest, including 140Ce, 153Eu, 165Ho, and 175Lu from the REE beads and 31P for the cells. The results achieved using the prototype instrument of a vertical downward-pointing ICP-TOFMS demonstrate that such a plasma configuration is well suited to analyze microplastics and single cells. For single microbead and cell analyses, the critical mass for carbon was 4.8 pg, and the mean determined carbon mass amounts were 14 and 23 pg, respectively. For the microbead analysis, the detected carbon mass corresponds to a particle diameter of 2.93 ± 0.24 µm, which is consistent with the scanning (transmission) electron microscopy-determined diameter of 2.97 ± 0.04 µm. Furthermore, in the analysis of spleenocyte cells, carbon and phosphorus masses were determined to be correlated.

Multielement analysis of single red blood cells by single cell - inductively coupled plasma tandem mass spectrometry

A method for the analysis of essential metals (Fe, Cu, Mg, and Zn) and non-metals (P, S) in single red blood cells was developed by single cell (SC)-ICP-MS. The use of a triple quadrupole configuration (MS/MS) enabled an effective elimination of polyatomic interferences, which affect the accuracy of ICP-MS analysis using a single quadrupole mass analyzer. Fixation with glutaraldehyde for at least 90 days was developed to improve the quantification of elements in a single red blood cell. The experimental conditions were optimized while special attention was paid to the residence time of analytes in the plasma. Addition of a surfactant (0.05% (v/v) Tween80®) improved quantification of elements in fixed red blood cells. The detection limits obtained by SC-ICP-MS/MS were lower than for ICP-MS, especially for S and P (3 fg and 1.7 fg. cell-1 instead of 163 and 6.3 fg. cell-1, respectively).

Study of Legionella pneumophila treatment with copper in drinking water by single cell-ICP-MS

Legionella pneumophila is a persistent opportunistic pathogen that poses a significant threat to domestic water systems. Previous studies suggest that copper (Cu) is an effective antimicrobial in water systems. A rapid and sensitive quantification method is desired to optimize the conditions of L. pneumophila treatment by Cu and to better understand the interaction mechanisms between Cu and cells. In this study, we developed a highly sensitive single cell (SC)-ICP-MS method to monitor L. pneumophila cell concentration and track their uptake of Cu. The SC-ICP-MS method showed excellent sensitivity (with a cell concentration detection limit of 1000 cells/mL), accuracy (good agreement with conventional hemocytometry method), and precision (relative standard deviation < 5%) in drinking water matrix. The cupric ions (Cu2+) treatment results indicated that the total L. pneumophila cell concentration, Cu mass per cell, colony-forming unit counting, and Cu concentration in supernatant all exhibited a dose-dependent trend, with 800-1200 µg/L reaching high disinfection rates in drinking water. The investigation of percentages of viable and culturable, viable but nonculturable (VBNC), and lysed cells suggested there always were VBNC present at any Cu concentration. Experimental results of different Cu2+ treatment times further suggested that L. pneumophila cells developed an antimicrobial resistant mechanism with the prolonged Cu exposure. This is the first quantification study on the interactions of Cu and L. pneumophila in drinking water using SC-ICP-MS.

Expanding the boundaries of atomic spectroscopy at the single-cell level: critical review of SP-ICP-MS, LIBS and LA-ICP-MS advances for the elemental analysis of tissues and single cells

Metals have a fundamental role in microbiology, and accurate methods are needed for their identification and quantification. The inability to assess cellular heterogeneity is considered an impediment to the successful treatment of different diseases. Unlike bulk approaches, single-cell analysis allows elemental heterogeneity across genetically identical populations to be related to specific biological events and to the effectiveness of drugs. Single particle-inductively coupled plasma-mass spectrometry (SP-ICP-MS) can analyse single cells in suspension and measure this heterogeneity. Here we explore advances in instrumental design, compare mass analysers and discuss key parameters requiring optimisation. This review has identified that the effect of pre-treatment of cell suspensions and cell fixation approaches require further study and novel validation methods are needed as using bulk measurements is unsatisfactory. SP-ICP-MS has the advantage that a large number of cells can be analysed; however, it does not provide spatial information. Techniques based on laser ablation (LA) enable elemental mapping at the single-cell level, such as laser-induced breakdown spectroscopy (LIBS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The sensitivity of commercial LIBS instruments restricts its use for sub-tissue applications; however, the capacity to analyse endogenous bulk components paired with developments in nano-LIBS technology shows great potential for cellular research. LA-ICP-MS offers high sensitivity for the direct analysis of single cells, but standardisation requires further development. The hyphenation of these trace elemental analysis techniques and their coupling with multi-omic technologies for single-cell analysis have enormous potential in answering fundamental biological questions.

Roles of DNA Target in Cancer Cell-Selective Cytotoxicity by Dicopper Complexes with DNA Target/Ligand Conjugates

The DNA target/ligand conjugates (HLX, X = Pn and Mn, n = 1-3) were synthesized where various lengths of -CONH(CH2CH2O)nCH2CH2NHCO- linkers with a 9-phenanthrenyl (P) or methyl (M) terminal as DNA targets replace the methyl group of 2,6-di(amide-tether cyclen)-p-cresol ligand (HL). DNA binding, DNA cleavage, cellular uptake, and cytotoxicity of [Cu2(μ-OH)(LX)](ClO4)2 (1X) are examined and compared with those of [Cu2(μ-OH)(L)](ClO4)2 (1) to clarify roles of DNA targets. Upon reaction of 1X with H2O2, μ-1,1-O2H complexes are formed for DNA cleavage. 1P1, 1P2, and 1P3 are 22-, 11-, 3-fold more active for conversion of Form II to III in the cleavage of supercoiled plasmid DNA with H2O2 than 1, where the short P-linker may fix a dicopper moiety within a small number of base pairs to facilitate DNA double-strand breaks (dsb). This enhances the proapoptotic activity of 1P1, 1P2, and 1P3, which are 30-, 12-, and 9.9-fold cytotoxic against HeLa cells than 1. DNA dsb and cytotoxicity are 44% correlated in 1P1-3 but 5% in 1M1-3, suggesting specific DNA binding of P-linkers and nonspecific binding of M-linkers in biological cells. 1P1-3 exert cancer cell-selective cytotoxicity against lung and pancreas cancer and normal cells where the short P-linker enhances the selectivity, but 1M1-3 do not. Intracellular visualization, apoptosis assay, and caspase activity assay clarify mitochondrial apoptosis caused by 1P1-3. The highest cancer cell selectivity of 1P1 may be enabled by the short P-linker promoting dsb of mitochondrial DNA with H2O2 increased by mitochondrial dysfunction in cancer cells.

Bi-Functionalized Transferrin@MoS2-PEG Nanosheets for Improving Cellular Uptake in HepG2 Cells

Pre-coating with a protein corona on the surface of nanomaterials (NMs) is an important strategy for reducing non-specific serum protein absorption while maintaining targeting specificity. Here, we present lipoic acid-terminated polyethylene glycol and transferrin bi-functionalized MoS₂ nanosheets (Tf@MoS₂-PEG NSs) as a feasible approach to enhance cellular uptake. Tf@MoS₂-PEG NSs can maintain good dispersion stability in cell culture medium and effectively protect MoS₂ NSs from oxidation in ambient aqueous conditions. Competitive adsorption experiments indicate that transferrin was more prone to bind MoS₂ NSs than bovine serum albumin (BSA). It is noteworthy that single HepG2 cell uptake of Tf@MoS₂-PEG presented a heterogeneous distribution pattern, and the cellular uptake amount spanned a broader range (from 0.4 fg to 2.4 fg). Comparatively, the intracellular Mo masses in HepG2 cells treated with BSA@MoS₂-PEG and MoS₂-PEG showed narrower distribution, indicating homogeneous uptake in the single HepG2 cells. Over 5% of HepG2 cells presented uptake of the Tf@MoS₂-PEG over 1.2 fg of Mo, about three-fold that of BSA@MoS₂-PEG (0.4 fg of Mo). Overall, this work suggests that Tf coating enhances the cellular uptake of MoS₂ NSs and is a promising strategy for improving the intracellular uptake efficiency of cancer cells.

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.

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.

Capabilities of Single Cell ICP-MS for the Analysis of Cell Suspensions from Solid Tissues

Single cell elemental (SC) analysis of isogenic cell cultures can be done using inductively coupled plasma (ICP-MS) detection. However, 2D cell cultures are just models to simplify the complexity of real tissue samples. Here, we show for the first time the capabilities of the technique (SC-ICP-MS) to analyze single cell suspensions of isolated cells from tissues. An optimized cocktail of proteolytic and collagenolytic enzymes was applied in a single preparation step with cellular yields up to 28% using 0.5 g of fresh rat spleen and liver, respectively. The retrieved cells revealed adequate morphology and stability to be examined by SC-ICP-MS. Quantitative elemental analysis of P, S, Cu, and Fe from disaggregated cells from rat spleen and liver tissues revealed levels of Fe of 7-16 fg/cell in the spleen and 8-12 fg/cell in the liver, while Cu was about 3-5 fg/cell in the spleen and 1.5-2.5 fg/cell in the liver. Evaluation of the transmembrane protein transferrin receptor 1 (TfR1) expression levels in disaggregated cells was also conducted by using a Nd-labelled antibody against this cell surface biomarker. Quantitative results showed significantly lower expression in the disaggregated cells than in the cell model HepG2, in agreement with the overexpression of this biomarker in tumor cells. In this proof of concept study, the tissue disaggregation protocol has shown to maintain the elemental intracellular content of cells as well as the presence of relevant antigens. This opens a completely new area of research for SC-ICP-MS in tissue samples as a complementary strategy with validation capabilities.

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.

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.

A label-free technique to quantify and visualize gold nanoparticle accumulation at the single-cell level

Despite their wide bioapplications, potential health risks of gold nanoparticles (AuNPs) remain unclear. As a determinant of their risks, AuNP accumulation within a cell population is subject to cell-to-cell heterogeneity. Methods to simultaneously quantify and visualize intracellular AuNPs at the single-cell level are, however, lacking. Here we developed a novel label-free technique, based on hyperspectral imaging with enhanced darkfield microscopy (HSI-DFM), to visualize and quantify AuNP accumulation at the single-cell level. The identification ability of the hyperspectral libraries derived from extra- and intracellular AuNPs was compared. The spectral number in the libraries was optimized to maximize their identification ability while minimizing the identification time. In addition, a filtration method was established to merge spectral libraries from different cell lines based on their similarity. The intracellularly accumulated AuNPs as determined by HSI-DFM well correlated with those detected by inductively coupled plasma mass spectrometry. This validation allowed us to calculate the intracellular concentration of AuNPs at the single-cell level and to monitor the accumulation kinetics of AuNPs in living cells. The label-free method developed herein can be applied to other types of AuNPs differing in their physicochemical properties as well as other NPs, as long as they are detectable by HSI-DFM.

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.

Exploring the Extent of Phosphorus and Heavy Metal Uptake by Single Cells of Saccharomyces cerevisiae and Their Effects on Intrinsic Elements by SC-ICP-TOF-MS

The effect of six heavy metals, namely, silver (Ag), lead (Pb), palladium (Pd), copper (Cu), nickel (Ni), and chromium (Cr), on phosphorus (P) uptake by yeast was investigated by single-cell analysis using inductively coupled plasma time-of-flight mass spectrometry (SC-ICP-TOF-MS). It was found that the P content in cells with 1.55 g L^–1 P feeding after P starvation was increased by ∼70% compared to control cells. Heavy metals at 10 ppm, except Cu, had a negative impact on P accumulation by cells. Pd reduced the P content by 26% in single cells compared to control cells. Metal uptake was strongest for Ag and Pd (0.7 × 10^–12 L cell^–1) and weakest for Cr (0.05 × 10^–12 L cell^–1). Exposure to Cr markedly reduced (−50%) Mg in cells and had the greatest impact on the intrinsic element composition. The SC-ICP-TOF-MS shows the diversity of elemental content in single cells: for example, the P content under standard conditions varied between 12.4 and 890 fg cell^–1. This technique allows studying both the uptake of elements and sublethal effects on physiology at a single-cell level.

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).

Enhancement of Cancer-Cell-Selective Cytotoxicity by a Dicopper Complex with Phenanthrene Amide-Tether Ligand Conjugate via Mitochondrial Apoptosis

Dicopper complexes [Cu2(μ-OH)(Ln)](ClO4)2 [n = 1 (1) and 2 (2)] with a novel phenanthrene amide-tether ligand conjugate (HL1) and the original p-cresol-2,6-bis(amidecyclen) (HL2) were synthesized. A phenanthrene unit of 1...

Recent advances in copper analyses by inorganic mass spectrometry

Copper (Cu) participates in the biological redox reaction in the body, and its deficiency is fatal to the body. At the same time, Cu is extremely toxic when it exists in excess. Thus, the body has to tightly and spatiotemporally regulate the concentration of Cu within a physiological range by several groups of Cu-regulating proteins. However, entire mechanisms underlying the maintenance of Cu homeostasis in body and cells have not fully understood. It is necessary to analyze Cu itself in a body and in a cell to reveal the Cu homeostasis. In this review, recent advances in the analytical techniques to understand the Cu metabolism such as speciation, imaging and single-cell analysis of Cu were highlighted.

Ruthenium red: a highly efficient and versatile cell staining agent for single-cell analysis using inductively coupled plasma time-of-flight mass spectrometry

Staining of biological cells with heavy metals can increase their visibility in mass spectrometry. In this study, the potential of ruthenium red (RR) as a staining agent for single-cell analysis by inductively coupled plasma time-of-flight mass spectrometry (SC-ICP-TOF-MS) is explored using two different yeast strains and one algal species. Time-of-flight mass spectrometry allows the simultaneous detection of Ru and multiple intrinsic elements in single cells. Ru has a better correlation with Mg than with P in Saccharomyces cerevisiae (S. cerevisiae) cells. For the three tested strains, the staining efficiency of RR exceeded 96%; the staining strengths were 30-32 ag μm^-2 for the yeast cells and 59 ag μm^-2 for the algal cells. By deriving the cell volume of single cells from their Ru mass, the concentration of Mg and P in individual cells of S. cerevisiae can be calculated. Elemental concentrations of Mg and P were highly variable in the cell individuals, with their 25-75 percentile values of 0.10-0.19 and 0.76-2.07 fg μm^-3, respectively. RR staining has several advantages: it is fast, does not affect cell viability and is highly efficient. Provided that the shape of the individual cells of a culture is similar, Ru staining allows the elemental content to be directly correlated with the cell volume to accurately calculate the intracellular concentration of target elements in single cells. Therefore, RR can be a promising cell staining agent for future application in SC-ICP-TOF-MS research.

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.

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.

The stochastic association of nanoparticles with algae at the cellular level: Effects of NOM, particle size and particle shape

Association of nanoparticles (NPs) with algae likely plays a critical role in their transfer in aquatic food chains. Although our understanding of the ecotoxicity and fate of NPs in the environment is increasing, it is still unclear how the physicochemical properties of NPs influence their interaction with algae at cellular levels and how this is reflected at a population level. This is due to the limitation in the existing analytical techniques to quantify the association of NPs with cells. To fill this data gap, we applied the novel technique of single-cell inductively coupled plasma mass spectrometry to quantify the cellular association of gold (Au)-NPs with algal cells (Pseudokirchneriella subcapitata) as a function of particle size, shape (spherical 10 nm, spherical 60 nm, spherical 100 nm, rod-shaped 10 × 40 nm, and rod-shaped 50 × 100 nm), and surface chemistry [citrate and natural organic matter (NOM) coating] on a cell-by-cell basis. The association of Au-NPs with algal cells was found to be a random probability following a so-called stochastic process; after 72 h of exposure, less than 45% of the cell population accumulated NPs on their surface. The number of Au-NPs per cell was found to be heterogeneously distributed as some cells were associated with a significantly higher number (e.g. up to 600 spherical 10 nm particles per cell) of Au-NPs than other cells present in the medium. The presence of NOM on the surface of the particles decreased the percentage of cells containing NPs except for the spherical 60 nm Au-NPs. We conclude that some algae within a population can accumulate NPs on their surface and this accumulation is influenced by the size, shape, and surface chemistry of NPs. It is important to understand how NPs may enter aquatic food chains to assess the possible risk.

Inertial-Force-Assisted, High-Throughput, Droplet-Free, Single-Cell Sampling Coupled with ICP-MS for Real-Time Cell Analysis

Single-cell analysis facilitates perception into the most essential processes in life's mysteries. While it is highly challenging to quantify them at the single-cell level, where precise single-cell sampling is the prerequisite. Herein, a real-time single-cell quantitative platform was established for high-throughput droplet-free single-cell sampling into time-resolved (TRA) ICP-MS and real-time quantification of intracellular target elements. The concentrated cells (2 × 10⁶ cells mL^-1) were spontaneously and orderly aligned in a spiral microchannel with 104 periodic dimensional confined micropillars. The quantification is conducted simultaneously by internal standard inducing from another branch channel in the chip. The flow-rate-independent feature of single-cell focusing into an aligned stream within a wide range of fluidic velocities (100-800 μL min^-1) facilitates high-throughput, oil-free, single-cell introduction into TRA-ICP-MS. The system was used for real-time exploration of intracellular antagonism of Cu²⁺ against Cd²⁺. an obvious antagonistic effect was observed for the MCF-7 cell by culturing for 3, 6, 9, and 12 h with 100 μg L^-1 Cd²⁺ and 100 μg L^-1 Cu²⁺, and a rivalry rate of 12.8% was achieved at 12 h. At identical experimental conditions, however, limited antagonistic effect was encountered for a bEnd3 cell within the same incubation time period, with a rivalry rate of 4.81%. On the contrary, an antagonistic effect was not observed for the HepG2 cell by culturing for 6 h, while an obvious antagonistic effect was found by further culturing to 12 h, with a rivalry rate of 10.43%. For all three cell lines, significant heterogeneity was observed among individual cells.

Evaluating the treatment effectiveness of copper-based algaecides on toxic algae Microcystis aeruginosa using single cell-inductively coupled plasma-mass spectrometry

Single cell-inductively coupled plasma-mass spectrometry (SC-ICP-MS) is an emerging technology. In this work, we have developed a novel SC-ICP-MS method to quantify metal ions in individual cells of a toxic cyanobacterial species, Microcystis aeruginosa (M. aeruginosa), without complicated post-dosing sample preparation, and applied this method to study the treatment effectiveness of copper-based algaecides (cupric sulfate and EarthTec®) on the toxic algae M. aeruginosa. The developed SC-ICP-MS method uses new intrinsic metal element magnesium to determine real transport efficiency and cell concentration. The cell viability and microcystin-LR release by algaecide treatment were studied by flow cytometry and ultra-fast liquid chromatography-tandem mass spectrometry, respectively. The results showed that this novel method was very rapid, highly sensitive (detection limits of intracellular copper and magnesium were 65 ag/cell and 98 ag/cell, respectively), and reproducible (relative standard deviation within 12%). The algaecide effectiveness study further demonstrated that copper in the forms of cupric sulfate and copper-based algaecide EarthTec® successfully diminished M. aeruginosa populations. The higher the copper concentration used to treat the cells, the faster the speeds of copper uptake and cell lysis in the copper concentrations ranged from 0 to 200 μg/L of copper-based algaecide. The cells exhibit obvious heterogeneity in copper uptake. The result suggests that M. aeruginosa cells uptake and cumulate copper followed by cellular lysis and microcystin-LR release. These novel results indicated that though the copper-based algaecides could control this type of harmful algal bloom, further treatment to remove the released algal toxin from the treated water would be needed.

Recent advances in single-cell analysis by mass spectrometry

Cells are the most basic structural units that play vital roles in the functioning of living organisms. Analysis of the chemical composition and content of a single cell plays a vital role in ensuring precise investigations of cellular metabolism, and is a crucial aspect of lipidomic and proteomic studies. In addition, structural knowledge provides a better understanding of cell behavior as well as the cellular and subcellular mechanisms. However, single-cell analysis can be very challenging due to the very small size of each cell as well as the large variety and extremely low concentrations of substances found in individual cells. On account of its high sensitivity and selectivity, mass spectrometry holds great promise as an effective technique for single-cell analysis. Numerous mass spectrometric techniques have been developed to elucidate the molecular profiles at the cellular level, including electrospray ionization mass spectrometry (ESI-MS), secondary ion mass spectrometry (SIMS), laser-based mass spectrometry and inductively coupled plasma mass spectrometry (ICP-MS). In this review, the recent advances in single-cell analysis by mass spectrometry are summarized. The strategies of different ionization modes to achieve single-cell analysis are classified and discussed in detail.

Single-cell assay on microfluidic devices

Advances in microfluidic techniques have prompted researchers to study the inherent heterogeneity of single cells in cell populations.

Importance of Metal-Ion Exchange for the Biological Activity of Coordination Complexes of the Biomimetic Ligand N4Py

Metal coordination complexes can display interesting biological activity, as illustrated by the bleomycins (BLMs), a family of natural antibiotics that when coordinated to a redox-active metal ion, show antitumor activity. Yet, which metal ion is required for the activity in cells is still subject to debate. In this study, we described how different metal ions affect the intracellular behavior and activity of the synthetic BLM-mimic N, N-bis(2-pyridylmethyl)- N-bis(2-pyridyl)methylamine (N4Py). Our study shows that a mixture of iron(II), copper(II), and zinc(II) complexes can be generated when N4Py is added to cell cultures but that the metal ion can also be exchanged by other metal ions present in cells. Moreover, the combination of chemical data, together with the performed biological experiments, shows that the active complex causing oxidative damage to cells is the FeII-N4Py complex and not per se the metal complex that was initially added to the cell culture medium. Finally, it is proposed that the high activity observed upon the addition of the free N4Py ligand is the result of a combination of scavenging of biologically relevant metals and oxidative damage caused by the iron(II) complex.

Single-cell analysis by ICP-MS/MS as a fast tool for cellular bioavailability studies of arsenite

A fast and reliable single-cell ICP-MS/MS method is presented to determine the bioavailability of metal species as well as sulfur and phosphorus as internal control after re-suspension of cells in water.

New Frontiers of Metallomics: Elemental and Species-Specific Analysis and Imaging of Single Cells

Single cells represent the basic building units of life, and thus their study is one the most important areas of research. However, classical analysis of biological cells eludes the investigation of cell-to-cell differences to obtain information about the intracellular distribution since it only provides information by averaging over a huge number of cells. For this reason, chemical analysis of single cells is an expanding area of research nowadays. In this context, metallomics research is going down to the single-cell level, where high-resolution high-sensitive analytical techniques are required. In this chapter, we present the latest developments and applications in the fields of single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS), mass cytometry, laser ablation (LA)-ICP-MS, nanoscale secondary ion mass spectrometry (nanoSIMS), and synchrotron X-ray fluorescence microscopy (SXRF) for single-cell analysis. Moreover, the capabilities and limitations of the current analytical techniques to unravel single-cell metabolomics as well as future perspectives in this field will be discussed.

Single cell versus large population analysis: cell variability in elemental intracellular concentration and distribution

The quantification of elemental concentration in cells is usually performed by analytical assays on large populations missing peculiar but important rare cells. The present article aims at comparing the elemental quantification in single cells and cell population in three different cell types using a new approach for single cells elemental analysis performed at sub-micrometer scale combining X-ray fluorescence microscopy and atomic force microscopy. The attention is focused on the light element Mg, exploiting the opportunity to compare the single cell quantification to the cell population analysis carried out by a highly Mg-selective fluorescent chemosensor. The results show that the single cell analysis reveals the same Mg differences found in large population of the different cell strains studied. However, in one of the cell strains, single cell analysis reveals two cells with an exceptionally high intracellular Mg content compared with the other cells of the same strain. The single cell analysis allows mapping Mg and other light elements in whole cells at sub-micrometer scale. A detailed intensity correlation analysis on the two cells with the highest Mg content reveals that Mg subcellular localization correlates with oxygen in a different fashion with respect the other sister cells of the same strain. Graphical abstract Single cells or large population analysis this is the question!

Quantitative Evaluation of Cisplatin Uptake in Sensitive and Resistant Individual Cells by Single-Cell ICP-MS (SC-ICP-MS)

One of the main limitations to the Pt-therapy in cancer is the development of associated drug resistance that can be associated with a significant reduction of the intracellular platinum concentration. Thus, intracellular Pt concentration could be considered as a biomarker of cisplatin resistance. In this work, an alternative method to address intracellular Pt concentration in individual cells is explored to permit the evaluation of different cell models and alternative therapies in a relatively fast way. For this aim, total Pt analysis in single cells has been implemented using a total consumption nebulizer coupled to inductively coupled plasma mass spectrometric detection (ICP-MS). The efficiency of the proposed device has been evaluated in combination with flow cytometry and turned out to be around 25% (cells entering the ICP-MS from the cells in suspension). Quantitative uptake studies of a nontoxic Tb-containing compound by individual cells were conducted and the results compared to those obtained by bulk analysis of the same cells. Both sets of data were statistically comparable. Thus, final application of the developed methodology to the comparative uptake of Pt-species in cisplatin resistant and sensitive cell lines (A2780cis and A2780) was conducted. The results obtained revealed the potential of this analytical strategy to differentiate between different cell lines of different sensitivity to the drug which might be of high medical interest.

Facile total synthesis of lysicamine and the anticancer activities of the RuII, RhIII, MnII and ZnII complexes of lysicamine

Lysicamine is a natural oxoaporphine alkaloid, which isolated from traditional Chinese medicine (TCM) herbs and has been shown to possess cytotoxicity to hepatocarcinoma cell lines. Reports on its antitumor activity are scarce because lysicamine occurs in plants at a low content. In this work, we demonstrate a facile concise total synthesis of lysicamine from simple raw materials under mild reaction conditions, and the preparation of the Ru(II), Rh(III), Mn(II) and Zn(II) complexes 1–4 of lysicamine (LY). All the compounds were fully characterized by elemental analysis, IR, ESI-MS, ¹H and ¹³C NMR, as well as single-crystal X-ray diffraction analysis. Compared with the free ligand LY, complexes 2 and 3 exhibited superior in vitro cytotoxicity against HepG2 and NCI-H460. Mechanistic studies indicated that 2 and 3 blocked the cell cycle in the S phase by decreasing of cyclins A2/B1/D1/E1, CDK 2/6, and PCNA levels and increasing levels of p21, p27, p53 and CDC25A proteins. In addition, 2 and 3 induced cell apoptosis via both the caspase-dependent mitochondrial pathway and the death receptor pathway. in vivo study showed that 2 inhibited HepG2 tumor growth at 1/3 maximum tolerated dose (MTD) and had a better safety profile than cisplatin.