Assessing the level and distribution of selenium in selenized yeast cells using single cell ICP-MS analysis

Significance of the Topic

Trace elements such as phosphorus and selenium play critical roles in cellular biochemistry and human health, yet their distribution at the level of individual cells remains poorly understood.

Single-cell inductively coupled plasma mass spectrometry (ICP-MS) offers a direct way to quantify elemental content on a per-cell basis, revealing cell-to-cell variability that can impact biopharmaceutical quality control, nutritional supplement development, and fundamental biological studies.

Goals and Study Overview

This application note illustrates how single-cell ICP-MS, paired with appropriate software tools, can be deployed to measure and display the distribution of phosphorus and selenium in a cohort of selenized Saccharomyces cerevisiae cells.

The specific objectives were:

• To count individual yeast cells via the 31P16O+ signal as a proxy for cell presence.
• To determine the fraction of cells containing detectable selenium via the 80Se16O+ signal.
• To characterize the mass distribution of both elements across several hundred cells.

Methodology and Instrumentation

Cell Preparation:

• Certified reference lyophilized yeast (SELM-1 CRM) resuspended in water.
• Two centrifuge washes and dilution to ~50,000 cells/mL (verified by flow cytometry).

Instrumentation and Software:

• Thermo Scientific iCAP TQ ICP-MS with MicroMist™ HE U-Series nebulizer and total consumption spray chamber (Glass Expansion).
• Chemyx™ Fusion 100-X syringe pump for stable low-flow sample introduction (~10 µL/min).
• Thermo Scientific Qtegra™ ISDS Software with scQuant Plug-in for instrument control, data acquisition, and signal integration.
• Reaction cell operated in TQ-O2 mode to convert 31P+ to 31P16O+ and 80Se+ to 80Se16O+ to eliminate polyatomic interferences.
• Time-resolved analysis with 5 ms dwell time over 240 s total per run (including uptake and wash).
• Transport efficiency determined via 30 nm gold nanoparticles at 65 %.
• Detection limits ~0.2 µg/L for selenium (≈0.17 fg per cell).

Main Results and Discussion

Cell Counting and Detection Efficiency:

• Phosphorus signals corresponded to 68 % of flow-cytometry counts, reflecting transport efficiency.
• Selenium was detected in approximately 57 % of cells above the detection threshold.

Quantitative Element Mass per Cell:

• Phosphorus: mean ~37.0 fg/cell (median 30.9 fg; range 12–164 fg; SD ±23.1 fg).
• Selenium: mean ~18.6 fg/cell (median 16.8 fg; range 2.5–72.5 fg; SD ±12.5 fg).

Distribution Patterns:

• Phosphorus exhibited a broad distribution reflecting variable cell size and DNA content.
• Selenium distribution was narrower but evident only in a subset of cells, highlighting heterogeneity in selenium uptake or incorporation.

Visualization:

• Raw time-resolved signals show discrete transient peaks for each cell.
• Histogram and box-plot representations enable rapid assessment of population variability.

Benefits and Practical Applications

• Rapid quantification of trace elements in individual cells without chromatographic separation.
• Insights into cell population heterogeneity for process monitoring in fermentation and supplement production.
• Potential to screen cell-by-cell responses to trace element supplementation or stress.
• Integration into existing ICP-MS workflows via software-controlled sample delivery and data analysis.

Future Trends and Opportunities

Advances may include higher throughput via droplet generation, integration with separation techniques for speciation at the single-cell level, multi-isotope profiling, and coupling with imaging mass spectrometry to link elemental data with cellular morphology.

Such developments will further expand our understanding of trace element biology and enhance quality control in biopharmaceutical and nutraceutical manufacturing.

Conclusion

Single-cell ICP-MS using the iCAP TQ platform and scQuant Plug-in enables quantitative analysis of phosphorus and selenium at the individual cell level, uncovering population heterogeneity and delivering valuable insights for biological research and industrial applications.

References

1. Klein EA. Selenium and vitamin E cancer prevention trial; Ann. N.Y. Acad. Sci. 2004, 1031, 234–241.
2. Gilbert-López B, Dernovics M, Moreno-González D, Molina-Díaz A, García-Reyes JF. Detection of over 100 selenium metabolites in selenized yeast by liquid chromatography electrospray time-of-flight mass spectrometry; J. Chromatogr. B 2017, 1060, 84–90.
3. Álvarez-Fernández García R, Corte-Rodríguez M, Macke M, LeBlanc KL, Mester Z, Montes-Bayón M, Bettmer J. Addressing the presence of biologic selenium nanoparticles in yeast cells: analytical strategies based on ICP-TQ-MS; Analyst 2020, 145, 1457–1465.