Potentiometric dyes are used to monitor the electrical activity inside cells where it is not possible to insert an
electrode, such as the mitochondria. This technology is especially powerful for the study of patterns of activity in complex multicellular preparations. It also makes possible the measurement of spatial and temporal variations in membrane potentialalong the surface of single cells. Ideally, the electric potential is determined at very high impedance, so that virtually zero current flow occurs to interfere with cellular reactions.
Types of dyes
Fast dyes: These are amphiphilic membrane staining dyes which usually have a pair of hydrocarbon chains acting as membrane anchors and a hydrophilic group which aligns the
chromophoreperpendicular to the membrane/aqueous interface. The chromophore is believed to undergo a large electronic charge shift as a result of excitation from the ground to the excited state and this underlies the putative electrochromic mechanism for the sensitivity of these dyes to membrane potential. This molecule (dye) intercalates among the lipophilicpart of biological membranes. This orientation assures that the excitation induced charge redistribution will occur parallel to the electric field within the membrane. A change in the voltage across the membrane will therefore cause a spectral shift resulting from a direct interaction between the field and the ground and excited state dipole moments.
* Potentiometric dyes: Imaging electrical activity of cell membranes. Leslie M. Loew. Pure &Appl. Chern., Vol. 68, No. 7, pp. 1405-1409.1996.
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