Nature Chem. doi:10.1038/nchem.120 (2009)

The fluids in the different compartments inside cells vary in viscosity, with those in some parts as thin as water, and those in others more glutinous than olive oil.

Marina Kuimova of Imperial College London and her colleagues have now watched as a dying cell's fluids thicken. Their tool, and weapon, was a molecular rotor that gives off a fluorescent signal that varies according to its rotation rate and can be triggered with light to release reactive oxygen species, which harm the cell.

When the lights went on and the harmful oxygen species were released, the spin rates of the molecules slowed. The team thinks that the cell's internal fluids became drastically more viscous (shown as orange in picture) because the chemical assault increased crosslinking between molecules. Over time, the thickening slowed the rate at which further harmful reactions took place.