Energy dissipation of a Brownian particle in a viscoelastic fluid.

We evaluate the energy dissipation rate of an optically driven Brownian particle in a polymer solution utilizing the generalized version of Harada and Sasa's equality [Phys. Rev. Lett. 95, 130602 (2005)] by Deutsch and Narayan [Phys. Rev. E 74, 026112 (2006)]. The irreversible work of a small system is estimated from readily obtainable quantities. By adopting the time-dependent memory function obtained by microrheology measurement, directly obtained works are in excellent agreement with those calculated from the generalized fluctuation dissipation theorem for nonequilibrium steady states. This result implies that the colloidal particle in a polymer solution can be described by the generalized Langevin equation.