A sample capture unit comprising a housing defining an enclosed substrate chamber containing a substantially planar sample-capture substrate extending in a plane for receiving a skin-print thereon. The housing comprises: a first part having an aperture providing access to the substrate chamber for depositing a skin-print on the sample- capture substrate； and a second part movable relative to the first part, from a first position in which the aperture is uncovered so as to allow receipt of a sample on the sample- capture substrate, and into a second position in which the aperture is covered, thereby preventing access to the substrate chamber； the housing further comprises a retaining mechanism configured to retain the second part in the second position； and an element having a perimeter defined by a line of frangibility, which enables irreversible detachment of at least a part of the element so as to create an access port dimensioned to allow removal of the sample-capture substrate.
