ID-11-P-5978 Dual-mode microviscosity measurements using a molecular rotor

Viscosity of the cellular membrane has a significant impact on cellular processes, including on the diffusion of biomolecules within or through the membrane. Although measurement of viscosity on a microscopic scale is a challenging task, we have demonstrated1 that it can be achieved with the aid of molecular rotors, which are fluorophores with viscosity dependent fluorescence intensities and lifetimes. Microviscosity measurements are usually performed via Fluorescence Lifetime Imaging Microscopy (FLIM), which produces a spatial map of the lifetime of a molecular rotor in the object of interest. Alternatively, ratiometric imaging can be used if the molecular rotor exhibits a viscosity dependent intensity ratio between two peaks in its fluorescence spectrum.

In this work we have examined a molecular rotor MB, constructed as a porphyrin dimer, which is capable of measuring viscosity via both of the methods described above. Only a few such molecular rotors are reported in the literature, however, this provides a useful opportunity as it allows us to independently double check measured viscosity values. We performed the calibration of the rotor in methanol/glycerol mixtures of varying viscosity using both FLIM and ratiometric imaging (Figure 2). MB was then employed for measuring viscosity in (i) lipid monolayers made by coating water droplets in dodecane with the lipid of choice (Figure 1). Viscosity change upon irradiation was measured in saturated (DPhPC) and unsaturated (DOPC) lipid monolayers. (ii) Viscosity was measured in SK-OV-3 cells upon irradiation.