As a final remark, let us point out that MOFs are not perfect defect-free crystals. When MOFs layers are synthesized, the growing fronts inevitably coalesce leaving empty space with larger dimensions than the intrinsic (micro)porosity. This additional porosity is typically called Constructional Porosity, and it was proven to be the main factor controlling diffusional processes through MOF. This phenomenon adds one additional level of complexity to structureperformance relation in MOF-based SERS substrates. For example Lee et al. reported on molecular-scale interfacial cavities (i.e., constructional porosity) between the used Ag nanocubes and the ZIF-8 film grown by LPE method (Ag@ZIF-8), which enables preconcentrating of target CO2 analyte nearby the surface of the Ag nanocubes with no chemical bonding taking place. As it can be seen in Figure -g, bare Ag nanostructure modified with 4-MBT does not respond to CO2 contacted to its surface. However, when it is capped with ZIF-8, CO2 exposure leads to the appearance of respective Raman scattering peaks. Importantly, when pre-synthesized ZIF-8 particles are casted on the Ag-MBT array, the cavities generated are larger, and no preconcentration of CO2 takes place within the LSP decay length.