High-resolution intracellular viscosity measurement using time-dependent fluorescence anisotropy

A low-cost pulsed laser is used in conjunction with a homebuilt laser confocal-scanning epifluorescence microscope having submicron lateral and axial spatial resolution to determine cytoplasmic viscosity at specific intracytoplasmic locations in J774 mouse macrophage cells. Time-dependent fluorescence anisotropy measurements are made at each location and global deconvolution techniques are used to determine rotational correlation times. These rotational correlation times are related to the hydrated volume of 8-hydroxyperene-1,3,6-trisulfonic acid (HPTS) to calculate viscosity at specific points inside the cell. In the cytoplasmic areas measured, rotational correlation times of HPTS ranged from 0.186 ns to 0.411 ns, corresponding to viscosities ranging from 1.00 +/- 0.03 cP to 2.21+/- 0.05 cP.