Diffusion-mediated cellular processes, such as metabolism, signalling and transport, depend on the hydrodynamic properties of the intracellular matrix. Photodynamic therapy, used in the treatment of cancer, relies on the generation of short-lived cytotoxic agents within a cell on irradiation of a drug. The efficacy of this treatment depends on the viscosity of the medium through which the cytotoxic agent must diffuse. Here, spectrally resolved fluorescence measurements of a porphyrin-dimer-based molecular rotor are used to quantify intracellular viscosity changes in single cells. We show that there is a dramatic increase in the viscosity of the immediate environment of the rotor on photoinduced cell death. The effect of this viscosity increase is observed directly in the diffusion-dependent kinetics of the photosensitized formation and decay of a key cytotoxic agent, singlet molecular oxygen. Using these tools, we provide insight into the dynamics of diffusion in cells, which is pertinent to drug delivery, cell signalling and intracellular mass transport.
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M.K.K. is grateful to the EPSRC Life Sciences Interface programme for a personal fellowship. We thank STFC for funding access to the Central Laser Facility. This work was supported in part by the Danish National Research Foundation under a block grant for the Center for Oxygen Microscopy and Imaging.
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Kuimova, M., Botchway, S., Parker, A. et al. Imaging intracellular viscosity of a single cell during photoinduced cell death. Nature Chem 1, 69–73 (2009). https://doi.org/10.1038/nchem.120
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