The standard method of performing investigations in cell biology consists of studying the behavior of average populations to extract information of the events occurring at a cellular and molecular level. Despite the unquestionable amount of knowledge accumulated with this approach, a closer look at the behavior in a single-cell and even subcellular scale is becoming more desirable as a way to study rare event populations. This becomes possible with the advent of an increasing number of fluorescent probes, which are compatible with cell viability and permit the monitoring of the morphological and physiological changes of a single cell following a particular challenge. The number of observed events can be kept large to ensure adequate population statistics. Changes associated with morphological and physiological responses are encoded with fluorescence parameters such as intensity, wavelength and spatial localization variations and fluorescence lifetime. In addition to this, following a particular challenge, confocal microscopy is a powerful tool to track these changes over time. It also provides a method of following the behavior of a large number of cells even at high magnifications, due to its versatility and automatization capabilities.
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