ANNINE-6plus is a water soluble voltage sensitive dye (also called potentiometric dyes). This compound was developed at the Max Planck Institute for Biochemistry in Germany. It is used to optically measure the changes in transmembrane voltage of excitable cells, including neurons, skeletal and cardiac myocytes. ANNINE-6plus has a fractional fluorescent intensity change (ΔF/F per 100 mV change) of about 30% with single-photon excitation (~488 nm) and >50% with two-photon excitation (~1060 nm).