An inexpensive dual-excitation apparatus for fluorescence microscopy

Ion sensitive indicator molecules can be employed in conjunction with fluorescence microscopy in single cells to measure rapid changes in the intracellular concentration of several ionic species. A number of these probes (e.g. fura-2) require the capability of measuring emission intensity at two excitation wavelengths to quantitate properly intracellular ion concentration. We have developed a simple dual-excitation apparatus for use in such applications. The apparatus switches the excitation filter within 150 ms. This economical apparatus is well suited in situations where the ionic concentration of interest is changing relatively slowly. Moreover, by synchronizing the device's action with an external stimulus, rapid and reproducible ionic changes in excitable tissue also can be measured.