Single-cell analysis by capillary electrophoresis

Abstract

What is the earth most like? ... It is most like a single cell." -Lewis Thomas [1] Perhaps Lewis Thomas understood the struggle of exploring the earth as that of a single cell: the diverse terrain occupied by various organisms, the aqueous environment, and all the small nuances that make the world functional. To scrutinize the deepest of oceans and the highest of mountains, and to conquer every facet and function of our planet, as heterogeneous as it is, would be an accomplishment in itself.As we have better understood the overall nature of earth over time, so too have we achieved a greater understanding of many macroscopic biological processes in a variety of species. This has led scientists to ponder the purpose of increasingly smaller entities in assorted organisms. For those wishing to understand the function of a single cell in a heterogeneous environment, rapid progress in measurement technology has spawned both intriguing results and more challenging scientific queries. As we ponder on a more diminutive scale, from cellular cluster to single cell to subcellular compartment, the demands placed on analytical instrumentation are amplified, and perhaps no recent technique has greater potential for this application than single cell capillary electrophoresis (CE).Since the first assay of a single neuron from Helix aspersa by capillary liquid chromatography (cLC) and CE [2], many advances in microscale separations have been realized that improve the information obtained from single-cell assays. While chemical analysis of single cells has a long history, the range of cells and the number of chemical constituents that can be measured is rapidly growing. However, much more progress is necessary before a complete chemical inventory of a single cell can be obtained. Thus, recent and future research on single-cell CE is aimed at increasing sensitivity so that smaller quantities of a wider range of analytes can be measured. In addition, traditional sampling and detection techniques are challenged by the diminutive nature of many mammalian cells. Furthermore, the sheer number of cells in complex organisms requires improvements in the throughput of existing analytical methods. Ultimately, the desire for improved spatial, temporal, and chemical information helps to propagate advances in CE for single-cell samples.Advances in cell sampling have assisted in acquiring greater spatial information from a single cell. Efficient sampling requires small-diameter capillaries for analysis of minute cells and subcellular compartments. Many different types of sampling methodology are employed for single-cell CE, including whole-cell sampling, cytoplasmic or subcellular sampling, cell-release sampling, and extracellular sampling [3]. Whole-cell sampling requires drawing the entire cell into an etched capillary via a microscope, after which a plug of lysate is injected. As with many techniques involving single cells, sample throughput is poor, as manual injection with a microscope is necessary. However, a methodology for continuous auto...

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