  We have performed mid-infrared imaging of Barnard's Star, one of the nearest
stars to the Sun, using CanariCam on the 10.4 m Gran Telescopio Canarias. We
aim to investigate an area within 1-10 arcsec separations, which for the 1.83
pc distance of the star translates to projected orbital separations of 1.8-18
AU (P > 12 yr), which have not been explored yet with astrometry or radial
velocity programs. It is therefore an opportunity to enter the domain of
distances where most giant planets are expected to form. We performed deep
imaging in the N-band window (Si-2 filter, 8.7 {\mu}m) reaching a 3{\sigma}
detection limit of 0.85+/-0.18 mJy and angular resolution of 0.24 arcsec, close
to the diffraction limit of the telescope at this wavelength. A total of 80 min
on-source integration time data were collected and combined for the deepest
image. We achieved a dynamical range of 8.0+/-0.1 mag in the 8.7 {\mu}m band,
at angular separations from ~2 to 10 arcsec and of ~6-8 mag at 1-2 arcsec. No
additional sources were found. Our detectability limits provide further
constraints to the presence of substellar companions of the Barnard's Star.
According to solar metallicity evolutionary models, we can exclude companions
of masses larger than 15 MJup (Teff > 400 K), ages of a few Gyr, and located in
~3.6-18 AU orbits with a 3{\sigma} confidence level. This minimum mass is
approximately 5 MJup smaller than any previous imaging survey that explored the
surroundings of Barnard's Star could restrict.
