  We propose a potentially practical scheme to precisely measure the charge
numbers of small charged objects by optomechanical systems using
optomechanically induced transparency (OMIT). In contrast to the conventional
measurements based on the noise backaction on the optomechanical systems, our
scheme makes use of the small deformation of the mechanical resonator sensitive
to the charge number of the nearby charged object, which could achieve the
detection of a single charge. The relationship between the charge number and
the window width of the OMIT is investigated and the feasibility of the scheme
is justified by numerical simulation using currently available experimental
values.
