Excitation and detection of action potential induced fluorescence changes through a single monomode optical fiber

Optical fiber probes able to detect intracellular potential changes in individual cells, in vivo have been developed. One probe uses a single-mode optical fiber to direct laser light onto cells stained with the voltage-sensitive fluorescent dye WW781 and also return part of the resulting fluorescence to a detection system. Fractional changes in fluorescent intensity of 10^-3, obtained from frog heart cells immobilized in zero-calcium Ringer´s solution, are comparable to those reported for other optical methods. Even larger signals can be obtained through multimode fiber, but spatial resolution is lost. For hearts in normal-calcium Ringer´s solutions, very large reproducible motion-related artifacts were detected. Optical heterodyne fiber probes that have the ability to study cell electrical activity through membrane birefringence without any fluorescent dye are being developed