Sample capture unit 1 comprises housing 2 defining enclosed substrate chamber which contains planar sample-capture substrate 4. The housing comprises first part 31 having aperture 6 providing access for depositing a skin-print on the substrate. Second part 10, maybe a shutter, is movable from a first position in which the aperture is uncovered to a second position in which the aperture is covered, preventing access to the substrate, and the second part is retained by a retaining mechanism. The housing also comprises element 5, perhaps a snap-off cover with tab 52, having frangible perimeter 51: irreversible detachment of the element creates an access port (55, Fig. 4) to allow removal of the substrate for analysis. Access to the substrate may only be possible following immediate visual evidence of tampering. The substrate may comprise an absorbent or non-absorbent material, and may be compatible with paper-spray mass spectrometry.
