We quantified amino groups displayed on inorganic and organic surfaces in aqueous solution using different types of cleavable fluorescent compounds and an aldehyde dye. The cleavable fluorescent compounds were designed to bind covalently to amino groups and then liberated under specific conditions. Among the investigated materials, cleavable coumarin was most appropriate for the quantification of amino groups on silica and resin surfaces. The developed method can measure small amounts (similar to pmol/cm(2)) of amino groups on a flat polymeric surface, detecting only amino groups that are exposed to aqueous solution and available for surface immobilization of ligands and biomolecules.