“…Fortunately,r elativelyf ast and convenient measurements of viscosity can be achieved with an emergingc lass of fluorescent compounds-molecular rotors. [1,2] Previously,t hey have been used for viscosity sensing in polymers, [3,4] polymersomes, [5] aerosols, [6][7][8] model lipid bilayers, [9,10] protein aggregates, [11] and live cells. [12][13][14][15] Within cells, viscosity measurements have been performed in mitochondria, [16,17] lysosomes, [18] an endoplasmic reticulum, [19] anda plasma membrane.…”