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Abstract: The applicability of thin sol-gel films as selective interfaces in electrochemical sensors has been examined. This requires not only to create a selective interface but also to enable facile diffusion of the analytes across the films. Creation of selectivity has been aimed by molecularly imprinting an electroactive species in the course of sol-gel formation. We have focused primarily on imprinting an iron(II) complex, i.e., tris(2,2'-bipyridine)iron(II) (Fe(bpy)(3)(2+)), as a means of selectively determining iron(II) in aqueous solution. Hence, the effect of different parameters, such as the composition of the sol-gel film and the hydrolysis and drying time, on the diffusion of Fe(bpy)(3)(2+), has been studied. We find that diffusion can be remarkably enhanced upon adding polyethylene glycol or a surfactant, such as decanoic acid. Nevertheless, so far we have not been able to develop thin films, which exhibit selectivity towards this inorganic species. The difficulties in designing such selective interfaces for heavy metals as opposed to organic species is demonstrated by successfully applying the same approach for designing a selective interface for diethyl- p-nitrophenyl phosphate (paraoxon)