  We show that Bloch oscillations of ultracold fermionic atoms in the periodic
potential of an optical lattice can be used for a sensitive measurement of
forces at the micrometer length scale, e.g. in the vicinity of dielectric
surface. In particular, the proposed approach allows to perform a local and
direct measurement of the Casimir-Polder force which is, for realistic
experimental parameters, as large as 10^-4 gravity.
