Active microrheology was conducted in living cells by applying an optical-trapping force to vigorously-fluctuating tracer beads with feedback-tracking technology. The complex shear modulus G(ω)=G′(ω)−iG″(ω) was measured in HeLa cells in an epithelial-like confluent monolayer. We found that G(ω)∝(−iω)1/2 over a wide range of frequencies (1 Hz <ω/2π <10 kHz). Actin disruption and cell-cycle progression from G1 to S and G2 phases only had a limited effect on G(ω) in living cells.
