Colloids in confinements have structural and dynamic properties in some cases very different from bulk properties. In particular, when the width of the confinement is few times the particle size (both of sub-micron dimensions), the fluid may exhibit unexpected structures.We propose to use neutron spin-echo scattering techniquestudy the assembly of colloidal suspensions made of ~50nm silica particles in 200nm-wide grooves of a diffraction grating (used as the confining medium). We expect to observe layering and buckling depending on the fluid concentration. To probe both lateral and in-depth profiles of the confined colloids reflection (grazing-incidence) and transmission measurements will be performed for each colloidal concentration. Dynamical theory calculations, previously tested on bare gratings, will be used to analyze the spin-echo data.