Which Method is Best for Single-Cell Analysis? A Comparison of LC-MS and Nano-ESI-MS

Live single-cell metabolomics, a rapidly growing area of research, offers the possibility of offering unique insights into cellular function and heterogeneity. While single-cell isolation approaches based on capillary sampling are, in principle, compatible with either nano-electrospray ionization-mass spectrometry (nano-ESI-MS), where the cell is lysed and sprayed directly into a mass spectrometer, or liquid chromatography-mass spectrometry (LC-MS) for metabolomics analysis, there is currently are no data which indicates which of these approaches provide the best performance (metabolite coverage, reproducibility and sensitivity) for single-cell metabolomics. In response, a joint study between the University of Surrey (Guildford, United Kingdom), King's College London Guy's Hospital, and Leiden University (The Netherlands) has developed and compared two semi-targeted metabolomics methods (direct nano-ESI-MS and LC-MS) for detecting amino acids and other hydrophilic metabolites in single macrophages. A paper based on their work was published in Analytical Chemistry.¹

Studying small molecules within individual cells gives scientists a real-time snapshot of what is happening inside them; doing so helps explain how single cells function, differ from one another, and react to their environment, giving us the clear picture of how their genes and proteins work.^2,3 How well we can analyze individual cells depends heavily on the methods used to collect the samples. Recently, new techniques for isolating single cells have been developed, with each approach offering its own unique pros and cons depending on how it's being used.⁴

With nano-ESI-MS, rapid, low-volume analysis with minimal sample preparation is possible; this makes the technique attractive for high throughput and spatial metabolomics. A limitation of nano-ESI-MS, however, is poor reproducibility, ion suppression and limited openly available data analysis software.^5,6 The research team haspreviously demonstrated that lipids can be detected and annotated in single cells using LC-MS;^7-9 this technique offers chromatographic separation to reduce ion suppression and enables accurate quantification, in addition to untargeted compound annotation using many open-access data analysis solutions.^10-12 hese workflows, however, suffer from transfer losses from the capillary tip to the LC-MS vial, sample dilution, and low throughput due to chromatographic separation steps.¹³ “It is therefore timely,” write the authors of the study,¹ “to compare the performance of LC-MS and nano-ESI-MS methods for single-cell analysis.”

The authors of the study found it interesting that their results showed “that, even when using analytical-flow LC-MS, the coverage of metabolites is superior to the nano-ESI-MS method. We applied both methodologies to single THP-1 macrophages infected with fluorescent Mycobacterium bovis bacillus Calmette-Guérin (BCG), the vaccine strain of Mycobacterium tuberculosis. Infected cells were identified under a microscope and sampled into glass capillaries. Our results show that the LC-MS approach provides a much clearer distinction between infected and control cells than using nano-ESI-MS. LC-MS detected enrichment of several compounds in infected cells, including methionine, cysteine and taurine, highlighting reprogramming of sulfur metabolism during mycobacterial infection.”¹

“These findings,” the authors continued,¹ “establish a robust analytical framework for spatially resolved single-cell metabolomics and underscore its potential for uncovering infection-driven metabolic heterogeneity, with broad applications in infectious disease research, drug discovery, and clinical diagnostics.”

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References

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