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ratio imaging fluorescence microscopy

(Science: procedure) A method of measurement of intracellular pH or intracellular calcium levels, using a fluorescent probe molecule (see fura-2), in which the two different excitation wavelengths are used and the emitted light levels compared.

If emission at one wavelength is sensitive to the intracellular ion level and emission at the other wavelength is not, then standardisation for intracellular probe concentration, efficiency of light collection, inactivation of probe and thickness of cytoplasm can all be performed automatically.