Sol-gels are more porous, and present higher mechanical and thermal stability than hydrogels, which allows for their application in implantable sensors. Porous layers can form the external part of the electrode modification and act as a diffusional barrier, limiting access only to smallest analytes. In case of commercial applications, defined and specific parameters of pore size and their distribution are needed. Polymeric or silica-based membranes are a method of choice in this case due to biocompatibility, stability and easiness in application .