In close collaboration with Dr. L.Loew's group we have developed new potentiometric indicators for cardiac optical mapping. These membrane voltage sensitive styryl dyes have excitation wavelengths ranging above 700 nm and emission spectra extending to 900 nm. They provide excellent optical action potentials in all typical cardiac tissues (mouse, rat, guinea pig, pig). The voltage sensitivities of these new potentiometric indicators (7-20% in a variety of species) are as good as those of the widely used ANEP series of probes.
Near-infrared (NIR) dyes have better depth penetration in cardiac tissue because NIR light is significantly less scattered and absorbed than light of shorter wavelength. Consequently, NIR dyes provide advantages for optical mapping of thick cardiac tissues. Some modes of optical mapping (such as transillumination when light source and photodetector face opposite sides of tissue) significantly benefit from using NIR dyes. Possible use of inexpensive excitation sources such as red LED, red laser diodes (see Fig. 2), and HeNe lasers (at 633 nm) is a great advantage. The new dyes have excitation and emission spectra that are well separated from the blood absorption maximum (~580 nm), better than for any other known voltage-sensitive dyes. This allows us to effectively use them in optically mapping blood perfused tissues (see Fig. 3, excitation at 650nm, voltage-sensitive fluorescence at >715nm).
Finally, due to molecular engineering of the chromophore the new dyes provide a wide range of dye washout time constants (50-5000 s). This allows tailoring dye loading and washout to the specific application. The latest generation of near-infrared voltage-sensitive dyes, with further improved major characteristics, is patent pending.