A novel fluorescent sensor responsive to local viscosity in the lipid bilayer membranes was designed and
synthesized. The sensor changes its fluorescence intensity reflecting the local viscosity of its surrounding
medium. The fluorescence measurement showed that the sensor is capable of discriminating between
different phase states of lipid bilayer. In addition, the sensor visualized liquid-ordered microdomains on
giant vesicles in terms of the microviscosity with a simple fluorescence technique