  A quasi two-dimensional colloidal suspension is studied under the influence
of immobilisation (pinning) of a random fraction of its particles. We introduce
a novel experimental method to perform random pinning and, with the support of
numerical simulation, we find that increasing the pinning concentration
smoothly arrests the system, with a cross-over from a regime of high mobility
and high entropy to a regime of low mobility and low entropy. At the local
level, we study fluctuations in area fraction and concentration of pins and map
them to entropic structural signatures and local mobility, obtaining a measure
for the local entropic fluctuations of the experimental system.
