Selective covalent immobilization of ferritin on alumina

Selective and specific covalent immobilization and simultaneous suppression of nonspecific adsorption of the protein ferritin (FN) on the surfaces of polycrystalline α-alumina colloidal particles and single α-alumina crystals is demonstrated. FN immobilization is obtained by using a classical immobilization route and by combining either the organic silane 3-(triethoxysilyl)propylsuccinic anhydride (TESPSA) or (3-aminopropyl)triethoxysilane (APTES) with the zero-length cross linking system N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS). The combination of APTES or TESPSA with EDC/NHS leads to a stable FN binding via amide bonds. However, the authors demonstrate that the TESPSA-EDC/NHS system enables an overall higher amount of covalent immobilization and a simultaneous suppression of nonspecific FN adsorption. After TESPSA functionalization negatively charged carboxylic groups are formed and can at the same time both electrostatically repel the overall negatively charged FN proteins and react with EDC/NHS for FN covalent immobilization. Moreover, the authors show that by specifically controlling the FN concentration during the immobilization reaction, the molecule distribution and density of bound FN can be easily tuned. The approach presented enables to selectively immobilize FN at mild conditions on substrates with different geometries and is therefore relevant for the fabrication of biomimetic nanomaterials and two-dimensional FN arrays.