Abstract Separation of a disease marker as low as a single molecule from a complex tissue, is called Chemical Cytometry. It is not only the sampling techniques that are challenged by the smaller nature of cells. Increasing detection sensitivity is also an important area of research on single-cell analysis. In parallel to improvements in sampling technique is the rapid progress in detection techniques. The smaller size of a single cell requires increasingly more and more selective and sensitive detection methods. Sensitivity is needed because of the low levels of some cell proteins, for example, and selectivity is needed when the analysis is aimed at quantification of one or more of the sub cellular organelles in the presence of all the other cell chemicals. Traditionally, detection methods employed for cell analysis were absorbance, fluorescence, and electrochemistry. Most detectors employed for single-cell analysis so far have been either based on electrochemistry or laser-induced fluorescence (LIF), which show very low detection limits. Unfortunately, electrochemistry or LIF detectors for single cell analysis restrict the technique to electroactive or fluorescent molecules. Although fluorescent derivatizing reagents are often used to label non-fluorescent molecules, this labeling step complicates the process of single cell analysis and often poses problems such as incomplete reactions and multiple labeling products if the functional groups for labeling are more than one per molecule. For online coupling to the CE, time-of-flight mass spectrometry (TOF-MS) appears promising, because its fast spectral acquisition complements with the timescale for CE separation. Both electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) have been used for single-cell CE detection. As detection limits improve for MS, an increasing number of on-line and off-line mass spectrometric methods will likely be employed for single-cell analysis. In this presentation, the main focus is on Sampling techniques for Single-Cell Analysis and early disease diagnosis with specific examples of mitochondria sampling and aging. I will discuss a sheath-flow cuvette that would illustrate the fundamentals of flow cytometry and, when combined with LIF detection for capillary electrophoresis, it would be the most sensitive detection technique interfaced to the most powerful separation technique. For subcellular sampling and analysis also the interface between LIF and sheath-flow cuvette provides high enough sensitivity in order to quantitatively monitor mitochondria inside a single cell. Highlights: Aging, Early Disease Diagnosis, Capillary Electrophoresis with Laser Induced Fluorescence Detection (CELIF), Single Mitochondria Analysis, Single Cell Analysis, Counting Individual Molecules.

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