Drug permeation across 2D tissue models is commonly studied by growing the cells of the tissue of interest on the surface of a permeable filter support (see image on the right). The filter membrane is highly permebale so that the cell layer becomes the diffusion limiting entity. The target compound (radio- or fluorescence-labeled) is the then applied to the upper (apical) compartment and samples are taken from the lower (basal) compartment as a function of time. The area specific rate of target permeation defines the permeability of the tissue. Due to its integral nature this filter approach is, however, prone to errors as defects in the cell layer are likely to occur and it does not provide information on the permeation pathway.
By using mesoporous silicon surfaces as growth substrate for adherent cells we study the permeation of target molecules with subcellular lateral resolution (see image on the right). The pores in the substrate are used as a highly ordered array of nano-cuvettes that collect the target molecule at the site of its permeation across the cell layer. The content of the pores is analyzed by fluorescence microscopy or label-free by laterally resolved secondary ion mass spectrometry.