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non-invasive measurement

Non-invasive measurements are those that can be performed without directly contacting, or otherwise damaging, a living specimen. In the context of non-invasive measurement of cultured cells, it refers to an observation and measurement method that does not damage the cells. In a broad sense, this may include the use of non-toxic fluorescent stains, reaction with a reaction solution, and the genetic expression of fluorescent protein fusions for live cell observation. In a more narrow sense, it may refer only to observation methods free of any treatment, including staining, and even when the stain is considered non-toxic. In contrast, methods such as cell fixation and immunostaining, as well as methods for RNA and protein extraction, are considered to be very invasive. Such methods are applied as confirmatory tests, but the cells cannot be used again after evaluation.
In the process of culturing cells, it is necessary to confirm that the target cells are growing, to measure the confluency of the culture, and to determine the timing of subculture from observations of the state of cell proliferation made using a microscope (as necessary and without damaging the cells). Since changes in the environment, such as the illumination conditions used for observation, temperature, and CO₂ concentration, contribute to a more invasive environment, great care should be taken to ensure that observation of cells is either non-invasive or minimally invasive.