To better understand cell-to-cell heterogeneity, advanced analytical tools are in a growing demand for elucidating chemical compositions of each cell within a population. However, the progress of single-cell chemical analysis has been restrained by the limitations of small cell volumes and minute cellular concentrations. Here, we present a rapid and sensitive method for investigating the lipid profiles of isolated single cells using infrared matrix-assisted laser desorption electrospray ionization mass spectrometry (IR-MALDESI-MS). In this work, HeLa cells were dispersed onto a glass slide, and the cellular contents were ionized by IR-MALDESI and measured using a Q-Exactive HF-X mass spectrometer. Importantly, this approach does not require extraction and/or enrichment of analytes prior to MS analysis. Using this approach, 45 distinct lipid species, predominantly phospholipids, were detected and putatively annotated from the single HeLa cells. The proof-of-concept study demonstrates the feasibility and efficacy of IR-MALDESI-MS for rapid lipidomic profiling of single cells, which provides an important basis for future work on differentiation between normal and diseased cells at various developmental states, which can offer new insights into cellular metabolic pathways and pathological processes. Although not yet accomplished, we believe this approach can be readily used as an assessment tool to compare the number of identified species during source evolution and method optimization (intra-laboratory), and also disclose the complementary nature of different direct analytical approaches for the coverage of different types of endogenous analytes (inter-laboratory).

Graphical abstract

为了更好地了解细胞间的异质性，人们越来越需要先进的分析工具来阐明群体中每个细胞的化学成分。然而，单细胞化学分析的进展受到小细胞体积和微小细胞浓度的限制。在这里，我们提出了一种使用红外基质辅助激光解吸电喷雾电离质谱（IR-MALDESI-MS）研究分离单细胞脂质谱的快速而灵敏的方法。在这项工作中，HeLa 细胞分散在载玻片上，细胞内容物通过 IR-MALDESI 电离，并使用 Q-Exactive HF-X 质谱仪进行测量。重要的是，这种方法不需要在 MS 分析之前提取和/或富集分析物。使用这种方法，从单个 HeLa 细胞中检测到并推测注释了 45 种不同的脂质种类（主要是磷脂）。概念验证研究证明了 IR-MALDESI-MS 用于单细胞快速脂质组学分析的可行性和有效性，这为未来区分不同发育状态的正常细胞和患病细胞的工作提供了重要基础，从而可以提供新的方法。深入了解细胞代谢途径和病理过程。尽管尚未完成，但我们相信这种方法可以很容易地用作评估工具，以比较源进化和方法优化（实验室内）期间已识别物种的数量，并揭示不同直接分析方法的覆盖范围的互补性不同类型的内源分析物（实验室间）。

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