Microrheology in living cells
Intracellular stresses generated by molecular motors can actively modify cytoskeletal network causing changes in intracellular mechanical properties. We measure the intracellular mechanical properties using passive and optical tweezers-based active microrheology approaches and endogenous organelle particles as probes. Using the fluctuation-dissipation theorem, we compared the two approaches measurements and distinguished thermal and non-thermal fluctuations of mechanical properties in living cells.
(a) A sketch of an optical-tweezers-based cytorheometer. Optical tweezers were used to manipulate an intracellular granular structure (lamellar body, left circle) or an extracellular antibody-coated glass particle (right circle), G’(ω) and G”(ω). (b) Cells obtained by using intracellular organelles as probes. (c) Cells probed with anti-integrin conjugated silica particles attached to the plasma membrane. Solid lines represent a power-law fit to G’.
The imaginary part of the mechanical response function (a”) by active microrheology (dots) and the normalized power spectrum ωC(ω)/2kBT measured by passive microrheology (lines). The right figure shows experimental results of the non-thermal energy to the thermal energy as a function of frequencies.