  We report on the electric measurements of an individual Au nanoparticle with
an ultra-high contact resistance of about $10^{19} \Omega$. The high-impedance
measurements have been carried out by counting the electrons that are
transferred onto the particle. In order to do this, a carbon nanotube is used
as the electrode for the supply of electrons but also as the detector of the
charge transfer. Measurements using single-electron detection allow us to
determine the separation between the electron states in the Au nanoparticle,
which is about 4 meV, consistent with the charging energy of the particle.
Single-electron detection with nanotubes offers great promise for the study of
electron transfer in highly resistive molecular systems.
