  In dense and cold molecular clouds dust grains are surrounded by thick icy
mantles. It is however not clear if dust growth and coagulation take place
before the switch-on of a protostar. This is an important issue, as the
presence of large grains may affect the chemical structure of dense cloud
cores, including the dynamically important ionization fraction, and the future
evolution of solids in protoplanetary disks. To study this further, we focus on
L1544, one of the most centrally concentrated pre-stellar cores on the verge of
star formation, and with a well-known physical structure. We observed L1544 at
1.2 and 2 mm using NIKA, a new receiver at the IRAM 30 m telescope, and we used
data from the Herschel Space Observatory archive. We find no evidence of grain
growth towards the center of L1544 at the available angular resolution.
Therefore, we conclude that single dish observations do not allow us to
investigate grain growth toward the pre-stellar core L1544 and high sensitivity
interferometer observations are needed. We predict that dust grains can grow to
200 $\mu$m in size toward the central ~300 au of L1544. This will imply a dust
opacity change by a factor of ~2.5 at 1.2 mm, which can be detected using the
Atacama Large Millimeter and submillimeter Array (ALMA) at different
wavelengths and with an angular resolution of 2".
