Many fundamental functions of a cell strongly depend on delicate, but nevertheless dynamic balances of ions (e.g. calcium, magnesium), voltage potentials and pH between the cell’s cytosol and the surrounding extracellular space. Changes in these balances significantly alter a cell’s behavior and function. Therefore, measurements of intracellular ion, voltage and pH dynamics in real time are of tremendous interest for researchers in neuroscience, cell biology and cell physiology in general. In many cases, however, exact estimations of actual ion concentrations or relative changes in different locations in a cell or a cellular network are difficult with conventional fluorescence methods. The reason is that these methods do not take account of the fact that differences in cell morphology within different parts of a single cell or between cell types in cellular networks might influence the quality and quantity of emitted light. This can lead to substantial misinterpretations when dynamic changes of ion concentrations, voltage or pH are investigated. Ratiometric imaging techniques bypasses these issues by observing emission wavelength shifts of fluorophores or by comparing the emission intensity of a fluorophore combination instead of measuring mere intensity changes.
of 14.7-fold, from 162.2 in the absence of Cr3+ to 11.0 in the presence
of Cr3+ (40 equiv.). More importantly, the good linearity between the
emission ratios (F425/F594) and the concentrations of Cr3+ allowed the
detection of Cr3+ by a ratiometric fluorescence method.