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Published online by Cambridge University Press: 31 January 2011
The combination of active and passive microrheology using magnetic probes engulfed inside living cells demonstrates the violation of the fluctuation dissipation theorem in cells. It is proposed to quantify the deviation from the in equilibrium situation with an effective temperature. Each magnetic probe then serves as a local thermometer within the cells. The response of pairs of magnetic beads of two diameters (1 and 2.8 μm) to an oscillating magnetic field is analyzed to measure the viscoelastic complex modulus in the beads environment (active measurement). The spontaneous motion of the beads is tracked to compute their mean square displacements (passive measurement). The effective temperature is derived using an extension of the fluctuation dissipation theorem.