Inductively Coupled Plasma Mass Spectrometry for the Analysis of Metal Content in Single Chinese Hamster Ovary Cells

Significance of the Topic

Single-cell inductively coupled plasma mass spectrometry (ICP-MS) enables quantitation of trace elements within individual cells rather than bulk populations. This capability is crucial for understanding cell‐to‐cell variability in metal uptake and distribution, which impacts bioprocess optimization, therapeutic protein production, and fundamental cell biology.

Study Objectives and Overview

The study aimed to develop and validate a complete workflow for single‐cell ICP-MS analysis of Chinese Hamster Ovary (CHO) K1 cells, focusing on iron quantitation. Objectives included system suitability assessment, reliable cell preparation, transient signal acquisition, and comparison with conventional bulk‐cell measurements.

Methodology and Instrumentation

• Cell Culture and Preparation: Two CHO K1 cell lines were maintained in CD medium, washed three times with Tris‐buffered saline (TBS), and viability assessed at 2–8 °C.
• Reference Materials: Gold nanospheres (100 nm), europium beads (3 μm), and selenized yeast (SELM-1) established system performance.
• Instrumentation Used:
  • Thermo Scientific iCAP TQ ICP-MS equipped with kinetic energy discrimination (KED) and triple quadrupole (TQ) modes.
  • Glass Expansion single‐cell sample introduction system with custom nebulizer and spray chamber.
  • Software: Thermo Scientific Qtegra OS for data acquisition and in-house application for automated transient peak detection and correction.
• ICP-MS Parameters: 2.0 mm quartz injector, nebulizer flow 0.5 L/min, additional gas 0.4 L/min, RF power 1550 W, sample flow 10 μL/min, dwell time 5 ms, total 6 min per sample.
• Data Acquisition: KED mode for 57Fe quantitation; TQ-O2 mode for 31P and 80Se oxide detection.

Key Results and Discussion

• System Verification: Nanoparticles and selenized yeast yielded sensitivity and accuracy matching literature, confirming single‐cell setup suitability.
• Cell Viability: Both CHO lines retained >95% viability after TBS washes and storage at 2–8 °C.
• Background Removal: Elemental levels in TBS supernatant dropped below quantitation limits (<0.006 mg/L Fe), ensuring minimal interference.
• Iron Distribution: Transient 57Fe signals in CHO K1 line 2 revealed cell‐to‐cell variability; average single‐cell iron was 15.5–16.3 fg, comparable to bulk‐cell averages (11.4–23.3 fg).

Practical Benefits and Applications

• Provides detailed single‐cell metal profiles to guide optimization of cell culture media and bioprocesses.
• Enhances quality control by detecting subpopulations with aberrant metal uptake.
• Offers a platform for studying trace element roles in cell physiology, drug response, and disease models.

Future Trends and Applications

• Extension to other cell lines, primary cells, and suspension cultures for broader biotechnological and clinical research.
• Integration with high‐throughput microfluidics and single‐cell multiomics for comprehensive phenotypic profiling.
• Development of automated data analysis pipelines leveraging machine learning to interpret complex elemental distributions.

Conclusions

A robust workflow for CHO cell single‐cell ICP-MS was established, demonstrating high viability, low background, and reliable transient signal acquisition. Single‐cell iron quantitation yielded results consistent with bulk analysis while revealing distribution heterogeneity. This approach offers new insights into cellular metal homeostasis and bioprocess control.

References

1. Theiner S. et al. Single-cell analysis by use of ICP-MS. J Anal At Spectrom. 2020.
2. Álvarez-Fernández García A. et al. Addressing biogenic selenium nanoparticles in yeast by ICP-TQ-MS. Analyst. 2019.