Potentiometric dyes

Voltage-sensitive dyes, also known as potentiometric dyes, are dyes which change their spectral properties in response to voltage changes. They are able to provide linear measurements of firing activity of single neurons, large neuronal populations or activity of myocytes. Many physiological processes are accompanied by changes in cell membrane potential which can be detected with voltage sensitive dyes. Measurements may indicate the site of action potential origin, and measurements of action potential velocity and direction may be obtained.

Potentiometric dyes are used to monitor the electrical activity inside cell organelles where it is not possible to insert an electrode, such as the . 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 potential along the surface of single cells.

Fast-response probes: 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 chromophore perpendicular 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 lipophilic part 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.

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