  We demonstrate a simple method for rotational microrheology in complex
fluids, using micrometric wires. The three-dimensional rotational Brownian
motion of the wires suspended in Maxwell fluids is measured from their
projection on the focal plane of a microscope. We analyze the mean-squared
angular displacement of the wires of length between 1 and 40 microns. The
viscoelastic properties of the suspending fluids are extracted from this
analysis and found to be in good agreement with macrorheology data. Viscosities
of simple and complex fluids between 0.01 and 30 Pa.s could be measured. As for
the elastic modulus, values up to ~ 5 Pa could be determined. This simple
technique, allowing for a broad range of probed length scales, opens new
perspectives in microrheology of heterogeneous materials such as gels, glasses
and cells.
